diff --git a/pdf-umbenenner-adapter-in-gui/pom.xml b/pdf-umbenenner-adapter-in-gui/pom.xml
index 179440e..9a924dd 100644
--- a/pdf-umbenenner-adapter-in-gui/pom.xml
+++ b/pdf-umbenenner-adapter-in-gui/pom.xml
@@ -62,6 +62,11 @@
       <artifactId>mockito-junit-jupiter</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.assertj</groupId>
+      <artifactId>assertj-core</artifactId>
+      <scope>test</scope>
+    </dependency>
     <!--
       Monocle: headless JavaFX platform for GUI smoke tests.
       Provides the Glass platform implementation that runs JavaFX without a
diff --git a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiConfigurationEditorWorkspace.java b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiConfigurationEditorWorkspace.java
index f3300be..d1db99c 100644
--- a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiConfigurationEditorWorkspace.java
+++ b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiConfigurationEditorWorkspace.java
@@ -3,22 +3,37 @@ package de.gecheckt.pdf.umbenenner.adapter.in.gui;
 import java.io.File;
 import java.nio.file.Path;
 import java.nio.file.Paths;
-import java.util.LinkedHashMap;
+import java.util.ArrayList;
+import java.util.EnumMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.Supplier;
 
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.AiProviderFamilyStringConverter;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiApiKeyMerger;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiChangeState;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationEditorState;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationFileSnapshot;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationTemplateFactory;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationValues;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiEditorValidationResult;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiFieldFinding;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiMessageEntry;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiMessageSeverity;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiModelFieldContainer;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiProviderApiKeyState;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiProviderConfigurationState;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiVisibleProviderSection;
 import de.gecheckt.pdf.umbenenner.application.config.provider.AiProviderFamily;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor;
+import de.gecheckt.pdf.umbenenner.application.validation.editor.ApiKeyResolutionPort;
+import de.gecheckt.pdf.umbenenner.application.validation.editor.EditorConfigurationValidator;
+import de.gecheckt.pdf.umbenenner.application.validation.editor.EditorValidationFinding;
+import de.gecheckt.pdf.umbenenner.application.validation.editor.EditorValidationInput;
+import de.gecheckt.pdf.umbenenner.application.validation.editor.EditorValidationReport;
+import de.gecheckt.pdf.umbenenner.application.validation.editor.EditorValidationSeverity;
 import javafx.application.Platform;
 import javafx.geometry.Insets;
 import javafx.geometry.Pos;
@@ -28,6 +43,7 @@ import javafx.scene.control.Alert;
 import javafx.scene.control.Button;
 import javafx.scene.control.ButtonType;
 import javafx.scene.control.CheckBox;
+import javafx.scene.control.ComboBox;
 import javafx.scene.control.Label;
 import javafx.scene.control.ScrollPane;
 import javafx.scene.control.Separator;
@@ -39,6 +55,8 @@ import javafx.scene.layout.GridPane;
 import javafx.scene.layout.HBox;
 import javafx.scene.layout.Priority;
 import javafx.scene.layout.VBox;
+import javafx.scene.text.Text;
+import javafx.scene.text.TextFlow;
 import javafx.stage.DirectoryChooser;
 import javafx.stage.FileChooser;
 import javafx.stage.Stage;
@@ -63,11 +81,15 @@ import org.apache.logging.log4j.Logger;
  * be replaced by tests for deterministic verification without a running scene.
  *
  * <p>The "Pfade" section renders text fields with native file- and folder-chooser buttons for
- * all path-based configuration values. The "Provider" section renders two provider blocks
- * (Claude and OpenAI-compatible) side by side with individual fields for base URL, model,
- * timeout and API key. The "Verarbeitungslimits" section provides text fields for the numeric
- * limits and a checkbox for the sensitive-logging flag. "Tests" and "Meldungen" are structural
- * placeholders for functionality added in later iterations.
+ * all path-based configuration values. The "Provider" section contains a non-editable
+ * {@link ComboBox} for provider selection; only the currently selected provider block is
+ * visible while the hidden block's data is preserved in {@link GuiVisibleProviderSection}.
+ * Each provider block contains a model field container that switches between a non-editable
+ * {@link ComboBox} (when a remote model list is available) and a manual text field (when no
+ * list can be retrieved), as well as editable fields for base URL, timeout and API key.
+ * The "Verarbeitungslimits" section provides text fields for the numeric limits and a checkbox
+ * for the sensitive-logging flag. "Tests" and "Meldungen" are structural placeholders for
+ * functionality added in later iterations.
  *
  * <p>All filesystem checks (e.g. the overwrite confirmation for "Speichern unter") are
  * performed on a background worker thread. UI updates always return to the FX Application
@@ -87,7 +109,8 @@ public final class GuiConfigurationEditorWorkspace {
     final Label dirtyMarkerLabel = new Label("geändert");
     private final Label welcomeTitleLabel = new Label("Willkommen");
     private final Label welcomeTextLabel = new Label(WELCOME_TEXT);
-    private final TabPane tabPane = new TabPane();
+    /** Package-private to allow node lookups in smoke tests. */
+    final TabPane tabPane = new TabPane();
     private final VBox sectionsBox = new VBox(12);
     private final Button newButton = new Button("Neu");
     private final Button openButton = new Button("Öffnen");
@@ -105,6 +128,18 @@ public final class GuiConfigurationEditorWorkspace {
     GuiConfigurationEditorState editorState;
     private boolean welcomeGuidanceVisible;
 
+    /**
+     * Tracks which provider section is currently visible and preserves the hidden provider's
+     * state so it is not lost when the user switches providers. Updated by
+     * {@link #buildVisibleProviderSection()} when the provider section is refreshed, and
+     * by {@link #handleProviderSwitch(AiProviderFamily)} when the ComboBox selection changes.
+     * <p>
+     * May be {@code null} when the editor has not yet rendered a configuration with both
+     * known provider entries (e.g. on blank start before "Neu" or "Öffnen").
+     * Package-private to allow assertions in smoke tests.
+     */
+    GuiVisibleProviderSection visibleProviderSection;
+
     /**
      * Factory for the save-file chooser dialog; package-private to allow substitution in tests.
      * The default creates a standard {@link FileChooser} instance.
@@ -177,6 +212,68 @@ public final class GuiConfigurationEditorWorkspace {
      */
     Consumer<String> titleUpdateListener = title -> { };
 
+    /**
+     * Per-provider {@link GuiModelFieldContainer} instances, one for each known provider family.
+     * Populated in {@link #createProviderBlock(String, AiProviderFamily)} and registered with
+     * the {@link GuiModelCatalogCoordinator}. Package-private to allow assertions in smoke tests.
+     */
+    final Map<AiProviderFamily, GuiModelFieldContainer> modelFieldContainers =
+            new EnumMap<>(AiProviderFamily.class);
+
+    /**
+     * Coordinator that manages asynchronous model catalogue retrieval and result delivery.
+     * Package-private to allow thread-factory substitution in smoke tests.
+     */
+    final GuiModelCatalogCoordinator modelCatalogCoordinator;
+
+    /**
+     * Mutable list of pending message entries produced by the model catalogue coordinator
+     * and the editor validation. Entries are appended on the JavaFX Application Thread.
+     * Later GUI layers can read and display these entries. Package-private for test inspection.
+     */
+    final List<GuiMessageEntry> pendingMessages = new ArrayList<>();
+
+    /**
+     * The scrollable container node that renders the central message area.
+     * Rebuilt by {@link #refreshMessagesArea()} after each validation run or model-catalogue
+     * result. Package-private so smoke tests can assert on its child count.
+     */
+    final VBox messagesAreaBox = new VBox(4);
+
+    /**
+     * Maps property-key strings to their associated field-level error {@link Label} widgets.
+     * The map is populated when the "Pfade" section and each provider block are constructed.
+     * {@link #refreshFieldErrorLabels()} iterates the map and shows or hides each label based
+     * on the current {@link #pendingFieldFindings}. Package-private for test inspection.
+     */
+    final Map<String, Label> fieldErrorLabels = new java.util.HashMap<>();
+
+    /**
+     * Maps each provider family to the informational {@link Label} shown directly below its
+     * API-key input field. The label reports whether the effective key originates from an
+     * environment variable, a property value, or is absent.
+     * Package-private for test inspection.
+     */
+    final Map<AiProviderFamily, Label> apiKeyOriginLabels = new EnumMap<>(AiProviderFamily.class);
+
+    /**
+     * Mutable list of pending field-level findings produced by the editor validation.
+     * Entries are replaced on the JavaFX Application Thread after each validation run.
+     * Later GUI layers can read and render these findings directly below the affected fields.
+     * Package-private for test inspection.
+     */
+    final List<GuiFieldFinding> pendingFieldFindings = new ArrayList<>();
+
+    /**
+     * The most recent editor validation result. Holds the combined messages and field findings
+     * from the last completed validation run. Never {@code null}; starts as an empty result.
+     * Package-private for test inspection.
+     */
+    GuiEditorValidationResult lastValidationResult = GuiEditorValidationResult.empty();
+
+    private final EditorConfigurationValidator editorValidator = new EditorConfigurationValidator();
+    private final ApiKeyResolutionPort apiKeyResolutionPort;
+
     /**
      * Creates a new workspace with the unloaded start state.
      *
@@ -199,6 +296,11 @@ public final class GuiConfigurationEditorWorkspace {
         this.configurationFileWriter = effectiveContext.configurationFileWriter();
         this.editorState = effectiveContext.initialState();
         this.welcomeGuidanceVisible = editorState.isNewConfiguration();
+        this.apiKeyResolutionPort = effectiveContext.apiKeyResolutionPort();
+
+        this.modelCatalogCoordinator = new GuiModelCatalogCoordinator(
+                effectiveContext.modelCatalogPort(), pendingMessages);
+        this.modelCatalogCoordinator.postResultCallback = this::refreshAfterValidation;
 
         this.unsavedChangesGuard = new GuiUnsavedChangesGuard(
                 triggerLabel -> showUnsavedChangesDialog(triggerLabel));
@@ -327,6 +429,21 @@ public final class GuiConfigurationEditorWorkspace {
         return tabPane;
     }
 
+    /**
+     * Returns the most recent editor validation result.
+     * <p>
+     * The result is updated after every call to {@link #applyEditorState} and after every
+     * field change via {@link #updateValues}. The initial value before any configuration is
+     * loaded is an empty result with no findings.
+     * <p>
+     * This method is safe to call from any thread; the result object itself is immutable.
+     *
+     * @return the most recent validation result; never {@code null}
+     */
+    public GuiEditorValidationResult lastValidationResult() {
+        return lastValidationResult;
+    }
+
     /**
      * Returns the fixed section titles shown inside the single configuration tab.
      *
@@ -700,6 +817,7 @@ public final class GuiConfigurationEditorWorkspace {
         statusLabel.setVisible(false);
         statusLabel.setManaged(false);
         refreshView();
+        runEditorValidation();
     }
 
     private void configureRoot() {
@@ -786,6 +904,11 @@ public final class GuiConfigurationEditorWorkspace {
     }
 
     private void refreshSections() {
+        // Clear per-provider and per-field registries before rebuilding; new instances are
+        // registered inside the section builders below.
+        modelFieldContainers.clear();
+        fieldErrorLabels.clear();
+        apiKeyOriginLabels.clear();
         sectionsBox.getChildren().setAll(
                 createWelcomeCard(),
                 createPathsSection(),
@@ -821,6 +944,10 @@ public final class GuiConfigurationEditorWorkspace {
      * Quellordner and Zielordner use a {@link DirectoryChooser}. SQLite-Datei and Prompt-Datei
      * use a {@link FileChooser} with appropriate extension filters. All pickers preserve
      * Windows-style paths (including mapped drive letters such as {@code S:\}) unchanged.
+     * <p>
+     * Each path field registers a field-level error slot in {@link #fieldErrorLabels} keyed by
+     * the corresponding property key. The slots are populated and shown or hidden by
+     * {@link #refreshFieldErrorLabels()}.
      *
      * @return the card node for the "Pfade" section
      */
@@ -828,74 +955,86 @@ public final class GuiConfigurationEditorWorkspace {
         VBox card = createCardContainer();
         card.getChildren().add(sectionTitle("Pfade"));
 
-        GridPane grid = createFieldGrid();
-        int row = 0;
+        // Use a VBox instead of a plain GridPane so error slots can sit directly below each row.
+        VBox fieldRows = new VBox(0);
 
         // Quellordner
         TextField sourceFolderField = boundTextField(
                 editorState.values().sourceFolder(),
                 val -> updateValues(editorState.values().withSourceFolder(val)));
-        addPathRow(grid, row++, "Quellordner:", sourceFolderField, () -> {
-            String picked = pickDirectory("Quellordner auswählen", sourceFolderField.getText());
-            if (picked != null) {
-                sourceFolderField.setText(picked);
-                updateValues(editorState.values().withSourceFolder(picked));
-            }
-        });
+        Label sourceFolderErrorLabel = createFieldErrorLabel();
+        fieldErrorLabels.put("source.folder", sourceFolderErrorLabel);
+        fieldRows.getChildren().add(buildPathFieldRow("Quellordner:", sourceFolderField,
+                sourceFolderErrorLabel, () -> {
+                    String picked = pickDirectory("Quellordner auswählen", sourceFolderField.getText());
+                    if (picked != null) {
+                        sourceFolderField.setText(picked);
+                        updateValues(editorState.values().withSourceFolder(picked));
+                    }
+                }));
 
         // Zielordner
         TextField targetFolderField = boundTextField(
                 editorState.values().targetFolder(),
                 val -> updateValues(editorState.values().withTargetFolder(val)));
-        addPathRow(grid, row++, "Zielordner:", targetFolderField, () -> {
-            String picked = pickDirectory("Zielordner auswählen", targetFolderField.getText());
-            if (picked != null) {
-                targetFolderField.setText(picked);
-                updateValues(editorState.values().withTargetFolder(picked));
-            }
-        });
+        Label targetFolderErrorLabel = createFieldErrorLabel();
+        fieldErrorLabels.put("target.folder", targetFolderErrorLabel);
+        fieldRows.getChildren().add(buildPathFieldRow("Zielordner:", targetFolderField,
+                targetFolderErrorLabel, () -> {
+                    String picked = pickDirectory("Zielordner auswählen", targetFolderField.getText());
+                    if (picked != null) {
+                        targetFolderField.setText(picked);
+                        updateValues(editorState.values().withTargetFolder(picked));
+                    }
+                }));
 
         // SQLite-Datei
         TextField sqliteField = boundTextField(
                 editorState.values().sqliteFile(),
                 val -> updateValues(editorState.values().withSqliteFile(val)));
-        addPathRow(grid, row++, "SQLite-Datei:", sqliteField, () -> {
-            String picked = pickFile("SQLite-Datei auswählen", sqliteField.getText(),
-                    new FileChooser.ExtensionFilter("SQLite-Dateien", "*.db", "*.sqlite", "*.sqlite3"),
-                    new FileChooser.ExtensionFilter("Alle Dateien (*.*)", "*.*"));
-            if (picked != null) {
-                sqliteField.setText(picked);
-                updateValues(editorState.values().withSqliteFile(picked));
-            }
-        });
+        Label sqliteErrorLabel = createFieldErrorLabel();
+        fieldErrorLabels.put("sqlite.file", sqliteErrorLabel);
+        fieldRows.getChildren().add(buildPathFieldRow("SQLite-Datei:", sqliteField,
+                sqliteErrorLabel, () -> {
+                    String picked = pickFile("SQLite-Datei auswählen", sqliteField.getText(),
+                            new FileChooser.ExtensionFilter("SQLite-Dateien", "*.db", "*.sqlite", "*.sqlite3"),
+                            new FileChooser.ExtensionFilter("Alle Dateien (*.*)", "*.*"));
+                    if (picked != null) {
+                        sqliteField.setText(picked);
+                        updateValues(editorState.values().withSqliteFile(picked));
+                    }
+                }));
 
         // Prompt-Datei
         TextField promptField = boundTextField(
                 editorState.values().promptTemplateFile(),
                 val -> updateValues(editorState.values().withPromptTemplateFile(val)));
-        addPathRow(grid, row++, "Prompt-Datei:", promptField, () -> {
-            String picked = pickFile("Prompt-Datei auswählen", promptField.getText(),
-                    new FileChooser.ExtensionFilter("Textdateien", "*.txt", "*.md"),
-                    new FileChooser.ExtensionFilter("Alle Dateien (*.*)", "*.*"));
-            if (picked != null) {
-                promptField.setText(picked);
-                updateValues(editorState.values().withPromptTemplateFile(picked));
-            }
-        });
+        Label promptErrorLabel = createFieldErrorLabel();
+        fieldErrorLabels.put("prompt.template.file", promptErrorLabel);
+        fieldRows.getChildren().add(buildPathFieldRow("Prompt-Datei:", promptField,
+                promptErrorLabel, () -> {
+                    String picked = pickFile("Prompt-Datei auswählen", promptField.getText(),
+                            new FileChooser.ExtensionFilter("Textdateien", "*.txt", "*.md"),
+                            new FileChooser.ExtensionFilter("Alle Dateien (*.*)", "*.*"));
+                    if (picked != null) {
+                        promptField.setText(picked);
+                        updateValues(editorState.values().withPromptTemplateFile(picked));
+                    }
+                }));
 
-        // Runtime-Lock-Datei (optional)
+        // Runtime-Lock-Datei (optional) — no error slot needed (optional field)
         TextField lockField = boundTextField(
                 editorState.values().runtimeLockFile(),
                 val -> updateValues(editorState.values().withRuntimeLockFile(val)));
-        addSimpleRow(grid, row++, "Lock-Datei (optional):", lockField);
+        fieldRows.getChildren().add(buildSimpleFieldRow("Lock-Datei (optional):", lockField, null));
 
-        // Log-Verzeichnis (optional)
+        // Log-Verzeichnis (optional) — no error slot needed (optional field)
         TextField logDirField = boundTextField(
                 editorState.values().logDirectory(),
                 val -> updateValues(editorState.values().withLogDirectory(val)));
-        addSimpleRow(grid, row++, "Log-Verzeichnis (optional):", logDirField);
+        fieldRows.getChildren().add(buildSimpleFieldRow("Log-Verzeichnis (optional):", logDirField, null));
 
-        card.getChildren().add(grid);
+        card.getChildren().add(fieldRows);
         return card;
     }
 
@@ -904,13 +1043,22 @@ public final class GuiConfigurationEditorWorkspace {
     // =========================================================================
 
     /**
-     * Builds the "Provider" section with two visible provider blocks (Claude and
-     * OpenAI-compatible) arranged in a horizontal layout.
+     * Builds the "Provider" section with a non-editable {@link ComboBox} for provider selection,
+     * a "Modelle neu laden" button and a container that shows exactly one provider block at a time.
      * <p>
-     * Each block contains editable fields for base URL, model, timeout and API key. The
-     * structure is intentionally kept simple and without show/hide logic so that later
-     * iterations can attach a ComboBox-based selector without reinventing the underlying
-     * field layout.
+     * Only the block for the currently active provider is visible. The block for the hidden
+     * provider is kept in the scene graph with {@code setVisible(false)} and
+     * {@code setManaged(false)} so that no blank space appears. The hidden provider's field
+     * values are preserved in {@link #visibleProviderSection} and are not lost when switching.
+     * <p>
+     * The active provider is resolved from {@code editorState.values().activeProviderFamily()}.
+     * When the stored identifier does not match any known provider the first provider in
+     * alphabetical enum order (Claude) is used as a safe default, consistent with the
+     * behaviour of the standard template.
+     * <p>
+     * When the provider ComboBox selection changes, a model catalogue retrieval is triggered
+     * automatically via {@link GuiModelCatalogCoordinator#triggerModelRetrieval}. The "Modelle
+     * neu laden" button triggers the same retrieval path on demand.
      *
      * @return the card node for the "Provider" section
      */
@@ -918,42 +1066,187 @@ public final class GuiConfigurationEditorWorkspace {
         VBox card = createCardContainer();
         card.getChildren().add(sectionTitle("Provider"));
 
-        // Active provider display (read-only in this iteration; ComboBox follows later).
-        GridPane activeGrid = createFieldGrid();
-        TextField activeProviderField = boundTextField(
-                editorState.values().activeProviderFamily(),
-                val -> updateValues(editorState.values().withActiveProviderFamily(val)));
-        activeProviderField.setPromptText("z.B. claude oder openai-compatible");
-        addSimpleRow(activeGrid, 0, "Aktiver Provider:", activeProviderField);
-        card.getChildren().add(activeGrid);
+        // --- Determine which provider to make visible initially ---
+        AiProviderFamily initialProvider = resolveActiveProvider(editorState.values().activeProviderFamily());
 
-        // Two provider blocks side by side.
-        HBox providerBlocks = new HBox(16);
-        providerBlocks.setFillHeight(true);
+        // --- ComboBox for provider selection ---
+        ComboBox<AiProviderFamily> providerComboBox = new ComboBox<>();
+        providerComboBox.setEditable(false);
+        providerComboBox.setConverter(new AiProviderFamilyStringConverter());
+        providerComboBox.getItems().addAll(AiProviderFamily.CLAUDE, AiProviderFamily.OPENAI_COMPATIBLE);
+        providerComboBox.setValue(initialProvider);
 
+        // --- "Modelle neu laden" button ---
+        Button reloadModelsButton = new Button("Modelle neu laden");
+        reloadModelsButton.setId("modelle-neu-laden-button");
+        reloadModelsButton.setOnAction(event -> triggerModelRetrievalForCurrentProvider(providerComboBox));
+
+        HBox comboRow = new HBox(8, providerComboBox, reloadModelsButton);
+        comboRow.setAlignment(Pos.CENTER_LEFT);
+
+        Label activeProviderError = createFieldErrorLabel();
+        fieldErrorLabels.put("ai.provider.active", activeProviderError);
+
+        GridPane comboGrid = createFieldGrid();
+        comboGrid.add(new Label("Aktiver Provider:"), 0, 0);
+        comboGrid.add(comboRow, 1, 0);
+        card.getChildren().addAll(comboGrid, activeProviderError);
+
+        // --- Build both provider blocks ---
         VBox claudeBlock = createProviderBlock("Claude", AiProviderFamily.CLAUDE);
         VBox openaiBlock = createProviderBlock("OpenAI-kompatibel", AiProviderFamily.OPENAI_COMPATIBLE);
 
-        HBox.setHgrow(claudeBlock, Priority.ALWAYS);
-        HBox.setHgrow(openaiBlock, Priority.ALWAYS);
-        providerBlocks.getChildren().addAll(claudeBlock, openaiBlock);
+        // Apply initial visibility: only the active provider block is shown.
+        applyProviderBlockVisibility(claudeBlock, openaiBlock, initialProvider);
+
+        // --- Record the initial visible-provider section snapshot ---
+        visibleProviderSection = buildVisibleProviderSection(initialProvider);
+
+        // Container holds both blocks; layout renders only the managed/visible one.
+        VBox providerBlockContainer = new VBox(0, claudeBlock, openaiBlock);
+
+        card.getChildren().add(providerBlockContainer);
+
+        // --- Wire the ComboBox selection change to the switch logic ---
+        providerComboBox.valueProperty().addListener((obs, oldFamily, newFamily) -> {
+            if (newFamily == null || newFamily.equals(oldFamily)) {
+                return;
+            }
+            handleProviderSwitch(newFamily, claudeBlock, openaiBlock);
+            // Trigger automatic model retrieval for the newly selected provider.
+            triggerModelRetrievalForCurrentProvider(providerComboBox);
+        });
 
-        card.getChildren().add(providerBlocks);
         return card;
     }
 
+    /**
+     * Triggers a model catalogue retrieval for the provider currently shown in the given
+     * ComboBox. The retrieval reads the current provider state from the editor state, so it
+     * operates on live (potentially unsaved) field values.
+     * <p>
+     * Must be called on the JavaFX Application Thread.
+     *
+     * @param providerComboBox the provider selection ComboBox; must not be {@code null}
+     */
+    private void triggerModelRetrievalForCurrentProvider(ComboBox<AiProviderFamily> providerComboBox) {
+        AiProviderFamily family = providerComboBox.getValue();
+        if (family == null) {
+            return;
+        }
+        GuiProviderConfigurationState providerState = Optional.ofNullable(
+                editorState.values().providerConfiguration(family))
+                .orElse(GuiProviderConfigurationState.blank());
+        modelCatalogCoordinator.triggerModelRetrieval(family, providerState);
+    }
+
+    /**
+     * Resolves the active provider family from a raw configuration identifier string.
+     * <p>
+     * When the identifier matches a known provider family it is returned directly. When the
+     * identifier is blank, unknown or {@code null}, Claude is returned as the safe default
+     * (alphabetically first and the standard-template default).
+     *
+     * @param activeProviderIdentifier raw value of {@code ai.provider.active}; may be blank
+     * @return the resolved provider family; never {@code null}
+     */
+    private static AiProviderFamily resolveActiveProvider(String activeProviderIdentifier) {
+        return AiProviderFamily.fromIdentifier(activeProviderIdentifier)
+                .orElse(AiProviderFamily.CLAUDE);
+    }
+
+    /**
+     * Builds a {@link GuiVisibleProviderSection} snapshot from the current editor state for
+     * the given visible provider. The hidden provider is the other known family.
+     *
+     * @param visibleProvider the provider whose block is currently shown; must not be {@code null}
+     * @return a fresh snapshot reflecting the current editor state; never {@code null}
+     */
+    private GuiVisibleProviderSection buildVisibleProviderSection(AiProviderFamily visibleProvider) {
+        AiProviderFamily hiddenProvider = (visibleProvider == AiProviderFamily.CLAUDE)
+                ? AiProviderFamily.OPENAI_COMPATIBLE
+                : AiProviderFamily.CLAUDE;
+        GuiProviderConfigurationState visibleState = Optional.ofNullable(
+                editorState.values().providerConfiguration(visibleProvider))
+                .orElse(GuiProviderConfigurationState.blank());
+        GuiProviderConfigurationState hiddenState = Optional.ofNullable(
+                editorState.values().providerConfiguration(hiddenProvider))
+                .orElse(GuiProviderConfigurationState.blank());
+        return new GuiVisibleProviderSection(visibleProvider, visibleState, hiddenProvider, hiddenState);
+    }
+
+    /**
+     * Sets the visibility of the two provider blocks so that exactly the requested provider's
+     * block is visible while the other is hidden and unmanaged.
+     *
+     * @param claudeBlock    the Claude provider block node; must not be {@code null}
+     * @param openaiBlock    the OpenAI-compatible provider block node; must not be {@code null}
+     * @param visibleProvider the provider whose block should be shown; must not be {@code null}
+     */
+    private static void applyProviderBlockVisibility(
+            VBox claudeBlock, VBox openaiBlock, AiProviderFamily visibleProvider) {
+        boolean claudeVisible = (visibleProvider == AiProviderFamily.CLAUDE);
+        claudeBlock.setVisible(claudeVisible);
+        claudeBlock.setManaged(claudeVisible);
+        openaiBlock.setVisible(!claudeVisible);
+        openaiBlock.setManaged(!claudeVisible);
+    }
+
+    /**
+     * Handles a provider-switch event triggered by the provider {@link ComboBox}.
+     * <p>
+     * Sequence of operations on provider switch:
+     * <ol>
+     *   <li>The {@link #visibleProviderSection} snapshot is switched via
+     *       {@link GuiVisibleProviderSection#switchProvider()} so both provider states are
+     *       preserved without any data loss.</li>
+     *   <li>The {@code ai.provider.active} value in the editor state is updated to the
+     *       new provider's identifier.</li>
+     *   <li>Block visibility is updated: the newly active block becomes visible and managed,
+     *       the previously active block becomes invisible and unmanaged.</li>
+     * </ol>
+     * <p>
+     * The field values of the previously visible provider are already held in the editor
+     * state (they are updated on every keystroke via the field listeners), so no explicit
+     * read-back from the UI is needed here.
+     *
+     * @param newProvider the provider selected by the user; must not be {@code null}
+     * @param claudeBlock the Claude provider block node; must not be {@code null}
+     * @param openaiBlock the OpenAI-compatible provider block node; must not be {@code null}
+     */
+    private void handleProviderSwitch(AiProviderFamily newProvider, VBox claudeBlock, VBox openaiBlock) {
+        // Switch the visible-provider section snapshot.
+        if (visibleProviderSection != null) {
+            visibleProviderSection = visibleProviderSection.switchProvider();
+        } else {
+            visibleProviderSection = buildVisibleProviderSection(newProvider);
+        }
+
+        // Update ai.provider.active in the editor state.
+        updateValues(editorState.values().withActiveProviderFamily(newProvider.getIdentifier()));
+
+        // Apply visibility to the block nodes.
+        applyProviderBlockVisibility(claudeBlock, openaiBlock, newProvider);
+
+        LOG.debug("GUI-Editor: Providerwechsel zu '{}'.", newProvider.getIdentifier());
+    }
+
     /**
      * Builds one provider configuration block for the given provider family.
      * <p>
-     * The block is a named card container with fields for base URL, model, timeout and API key.
-     * All fields are wired to the editor state via the provider-specific updater path so that
-     * changes in one provider block do not affect the other.
+     * The block contains editable fields for base URL, timeout and API key, as well as a
+     * {@link GuiModelFieldContainer} for the model field. Field-level error slots are registered
+     * in {@link #fieldErrorLabels} keyed by their property key (e.g.
+     * {@code "ai.provider.claude.model"}). An API-key origin label is registered in
+     * {@link #apiKeyOriginLabels} for display of the effective key source.
      *
-     * @param displayName  the human-readable label shown as the block title
-     * @param family       the provider family this block represents
+     * @param displayName the human-readable label shown as the block title
+     * @param family      the provider family this block represents
      * @return the provider block as a styled card node
      */
     private VBox createProviderBlock(String displayName, AiProviderFamily family) {
+        String ns = "ai.provider." + family.getIdentifier() + ".";
+
         VBox block = new VBox(8);
         block.setStyle(
                 "-fx-padding: 10px; -fx-border-color: #c8c8c8; -fx-border-radius: 6px;"
@@ -967,31 +1260,52 @@ public final class GuiConfigurationEditorWorkspace {
                 editorState.values().providerConfiguration(family))
                 .orElse(GuiProviderConfigurationState.blank());
 
-        GridPane grid = createFieldGrid();
-        int row = 0;
+        VBox fieldRows = new VBox(0);
 
+        // Base-URL field
         TextField baseUrlField = boundTextField(pState.baseUrl(),
                 val -> updateProviderField(family, pState2 -> new GuiProviderConfigurationState(
                         val, pState2.model(), pState2.timeoutSeconds(), pState2.apiKey())));
-        addSimpleRow(grid, row++, "Basis-URL:", baseUrlField);
+        Label baseUrlError = createFieldErrorLabel();
+        fieldErrorLabels.put(ns + "baseUrl", baseUrlError);
+        fieldRows.getChildren().add(buildSimpleFieldRow("Basis-URL:", baseUrlField, baseUrlError));
 
-        TextField modelField = boundTextField(pState.model(),
+        // Model field — switches between ComboBox and manual text field.
+        GuiModelFieldContainer modelContainer = new GuiModelFieldContainer(
+                pState.model(),
                 val -> updateProviderField(family, pState2 -> new GuiProviderConfigurationState(
                         pState2.baseUrl(), val, pState2.timeoutSeconds(), pState2.apiKey())));
-        addSimpleRow(grid, row++, "Modell:", modelField);
+        modelFieldContainers.put(family, modelContainer);
+        modelCatalogCoordinator.registerFieldContainer(family, modelContainer);
+        Label modelError = createFieldErrorLabel();
+        fieldErrorLabels.put(ns + "model", modelError);
+        GridPane modelGrid = createFieldGrid();
+        modelGrid.add(new Label("Modell:"), 0, 0);
+        modelGrid.add(modelContainer.asNode(), 1, 0);
+        fieldRows.getChildren().addAll(modelGrid, modelError);
 
+        // Timeout field
         TextField timeoutField = boundTextField(pState.timeoutSeconds(),
                 val -> updateProviderField(family, pState2 -> new GuiProviderConfigurationState(
                         pState2.baseUrl(), pState2.model(), val, pState2.apiKey())));
-        addSimpleRow(grid, row++, "Timeout (Sek.):", timeoutField);
+        Label timeoutError = createFieldErrorLabel();
+        fieldErrorLabels.put(ns + "timeoutSeconds", timeoutError);
+        fieldRows.getChildren().add(buildSimpleFieldRow("Timeout (Sek.):", timeoutField, timeoutError));
 
+        // API-Key field with origin label below
         TextField apiKeyField = boundTextField(pState.apiKey().propertyValue(),
                 val -> updateProviderField(family, pState2 -> new GuiProviderConfigurationState(
                         pState2.baseUrl(), pState2.model(), pState2.timeoutSeconds(),
                         GuiProviderApiKeyState.unresolved(val))));
-        addSimpleRow(grid, row++, "API-Key:", apiKeyField);
+        Label apiKeyError = createFieldErrorLabel();
+        fieldErrorLabels.put(ns + "apiKey", apiKeyError);
+        Label apiKeyOriginLabel = createApiKeyOriginLabel();
+        apiKeyOriginLabels.put(family, apiKeyOriginLabel);
+        VBox apiKeySlot = buildSimpleFieldRow("API-Key:", apiKeyField, apiKeyError);
+        apiKeySlot.getChildren().add(apiKeyOriginLabel);
+        fieldRows.getChildren().add(apiKeySlot);
 
-        block.getChildren().add(grid);
+        block.getChildren().add(fieldRows);
         return block;
     }
 
@@ -1057,11 +1371,40 @@ public final class GuiConfigurationEditorWorkspace {
         return card;
     }
 
+    /**
+     * Builds the "Meldungen" section containing the central message area.
+     * <p>
+     * The central message area is a scrollable, non-editable container that displays all
+     * pending messages from the editor validation and model-catalogue coordinator. Each
+     * message is rendered as one {@link TextFlow} row in which only the severity prefix is
+     * coloured; the remainder of the text stays black.
+     * <p>
+     * The internal {@link #messagesAreaBox} is populated by {@link #refreshMessagesArea()} and
+     * is kept stable across section rebuilds via the persistent field reference so that later
+     * calls to {@code refreshMessagesArea()} always update the correct node.
+     *
+     * @return the card node for the "Meldungen" section
+     */
     private Node createMessagesSection() {
         VBox card = createCardContainer();
-        card.getChildren().addAll(
-                sectionTitle("Meldungen"),
-                textLabel("Sichtbare Meldungen und technische Hinweise folgen in einem späteren Schritt."));
+        card.getChildren().add(sectionTitle("Meldungen"));
+
+        messagesAreaBox.setFillWidth(true);
+        messagesAreaBox.setStyle("-fx-padding: 4px 0 0 0;");
+
+        ScrollPane scrollPane = new ScrollPane(messagesAreaBox);
+        scrollPane.setFitToWidth(true);
+        scrollPane.setHbarPolicy(ScrollPane.ScrollBarPolicy.NEVER);
+        scrollPane.setVbarPolicy(ScrollPane.ScrollBarPolicy.AS_NEEDED);
+        scrollPane.setPrefViewportHeight(140);
+        scrollPane.setMaxHeight(200);
+        scrollPane.setStyle("-fx-background-color: transparent; -fx-border-color: #d8d8d8;"
+                + " -fx-border-radius: 4px;");
+
+        card.getChildren().add(scrollPane);
+
+        // Populate immediately so the area is not blank before the first validation run.
+        refreshMessagesArea();
         return card;
     }
 
@@ -1070,7 +1413,7 @@ public final class GuiConfigurationEditorWorkspace {
     // =========================================================================
 
     /**
-     * Applies new general values to the editor state.
+     * Applies new general values to the editor state and triggers a revalidation.
      * <p>
      * Must be called on the FX Application Thread.
      *
@@ -1079,6 +1422,7 @@ public final class GuiConfigurationEditorWorkspace {
     private void updateValues(GuiConfigurationValues newValues) {
         this.editorState = editorState.withValues(newValues);
         refreshHeader();
+        runEditorValidation();
     }
 
     /**
@@ -1100,6 +1444,248 @@ public final class GuiConfigurationEditorWorkspace {
         updateValues(updated);
     }
 
+    // =========================================================================
+    // Editor validation
+    // =========================================================================
+
+    /**
+     * Runs the editor validation against the current editor state and stores the result
+     * in {@link #lastValidationResult}, {@link #pendingMessages} and {@link #pendingFieldFindings}.
+     * <p>
+     * This method is pure in-memory (no I/O) and may be called on the JavaFX Application Thread.
+     * Path existence checks, SQLite roundtrips and network calls are explicitly excluded from
+     * this validation and belong to later technical overall checks.
+     * <p>
+     * Must be called on the FX Application Thread.
+     */
+    private void runEditorValidation() {
+        GuiConfigurationValues values = editorState.values();
+        GuiProviderConfigurationState claudeState = Optional.ofNullable(
+                values.providerConfiguration(AiProviderFamily.CLAUDE))
+                .orElse(GuiProviderConfigurationState.blank());
+        GuiProviderConfigurationState openaiState = Optional.ofNullable(
+                values.providerConfiguration(AiProviderFamily.OPENAI_COMPATIBLE))
+                .orElse(GuiProviderConfigurationState.blank());
+
+        EffectiveApiKeyDescriptor claudeKeyDescriptor =
+                apiKeyResolutionPort.resolve(AiProviderFamily.CLAUDE,
+                        claudeState.apiKey().propertyValue());
+        EffectiveApiKeyDescriptor openaiKeyDescriptor =
+                apiKeyResolutionPort.resolve(AiProviderFamily.OPENAI_COMPATIBLE,
+                        openaiState.apiKey().propertyValue());
+
+        EditorValidationInput input = new EditorValidationInput(
+                values.activeProviderFamily(),
+                values.sourceFolder(),
+                values.targetFolder(),
+                values.sqliteFile(),
+                values.promptTemplateFile(),
+                values.maxRetriesTransient(),
+                values.maxPages(),
+                values.maxTextCharacters(),
+                claudeState.baseUrl(),
+                claudeState.model(),
+                claudeState.timeoutSeconds(),
+                claudeKeyDescriptor,
+                openaiState.baseUrl(),
+                openaiState.model(),
+                openaiState.timeoutSeconds(),
+                openaiKeyDescriptor);
+
+        EditorValidationReport report = editorValidator.validate(input);
+
+        // Translate to GUI types
+        List<GuiMessageEntry> messages = new ArrayList<>();
+        List<GuiFieldFinding> fieldFindings = new ArrayList<>();
+
+        for (EditorValidationFinding finding : report.findings()) {
+            GuiMessageSeverity severity = toGuiSeverity(finding.severity());
+            messages.add(GuiMessageEntry.of(severity, finding.message(), "Validierung"));
+            if (finding.hasFieldKey()) {
+                fieldFindings.add(new GuiFieldFinding(finding.fieldKey().orElseThrow(),
+                        severity, finding.message()));
+            }
+        }
+
+        // Replace validation-related entries; preserve model-catalog messages (from coordinator)
+        pendingMessages.removeIf(m -> m.source().isPresent()
+                && "Validierung".equals(m.source().get()));
+        pendingMessages.addAll(messages);
+
+        pendingFieldFindings.clear();
+        pendingFieldFindings.addAll(fieldFindings);
+
+        lastValidationResult = new GuiEditorValidationResult(
+                List.copyOf(pendingMessages),
+                List.copyOf(pendingFieldFindings),
+                java.time.Instant.now());
+
+        refreshAfterValidation();
+    }
+
+    /**
+     * Maps an {@link EditorValidationSeverity} to the corresponding {@link GuiMessageSeverity}.
+     *
+     * @param severity the application-layer severity; must not be {@code null}
+     * @return the corresponding GUI severity; never {@code null}
+     */
+    private static GuiMessageSeverity toGuiSeverity(EditorValidationSeverity severity) {
+        return switch (severity) {
+            case ERROR -> GuiMessageSeverity.ERROR;
+            case WARNING -> GuiMessageSeverity.WARNING;
+            case HINT -> GuiMessageSeverity.HINT;
+            case INFO -> GuiMessageSeverity.INFO;
+        };
+    }
+
+    /**
+     * Central refresh method called after every validation run and after every model-catalogue
+     * result arrives. Updates the central message area, the field-level error labels and the
+     * API-key origin labels in one consistent pass.
+     * <p>
+     * Must be called on the JavaFX Application Thread.
+     */
+    private void refreshAfterValidation() {
+        refreshMessagesArea();
+        refreshFieldErrorLabels();
+        refreshApiKeyOriginLabels();
+    }
+
+    // =========================================================================
+    // Message area rendering
+    // =========================================================================
+
+    /**
+     * Rebuilds the content of {@link #messagesAreaBox} from the current {@link #pendingMessages}
+     * list.
+     * <p>
+     * Each message is rendered as one {@link TextFlow} row. The severity prefix is coloured using
+     * the CSS colour from {@link GuiMessageSeverity#getPrefixCssColour()}; the remainder of the
+     * message text is always black. The placeholder text is shown when the list is empty.
+     * <p>
+     * Must be called on the JavaFX Application Thread.
+     */
+    void refreshMessagesArea() {
+        messagesAreaBox.getChildren().clear();
+        if (pendingMessages.isEmpty()) {
+            Text placeholder = new Text("Keine Meldungen vorhanden.");
+            placeholder.setStyle("-fx-fill: #888888;");
+            messagesAreaBox.getChildren().add(new TextFlow(placeholder));
+            return;
+        }
+        for (GuiMessageEntry entry : pendingMessages) {
+            Text prefix = new Text(entry.severity().getPrefixLabel() + " ");
+            prefix.setStyle("-fx-fill: " + entry.severity().getPrefixCssColour() + ";"
+                    + " -fx-font-weight: bold;");
+            Text body = new Text(entry.text());
+            body.setStyle("-fx-fill: black;");
+            TextFlow row = new TextFlow(prefix, body);
+            row.setStyle("-fx-padding: 1px 4px;");
+            messagesAreaBox.getChildren().add(row);
+        }
+    }
+
+    // =========================================================================
+    // Field-level error label rendering
+    // =========================================================================
+
+    /**
+     * Updates each field-level error label in {@link #fieldErrorLabels} from the current
+     * {@link #pendingFieldFindings} list.
+     * <p>
+     * For each registered field key, the most severe finding of severity {@link GuiMessageSeverity#ERROR}
+     * or {@link GuiMessageSeverity#WARNING} is selected and its text is shown in the label.
+     * Labels for fields without any relevant finding are hidden and unmanaged so they consume no
+     * layout space.
+     * <p>
+     * Must be called on the JavaFX Application Thread.
+     */
+    void refreshFieldErrorLabels() {
+        for (Map.Entry<String, Label> entry : fieldErrorLabels.entrySet()) {
+            String key = entry.getKey();
+            Label label = entry.getValue();
+            pendingFieldFindings.stream()
+                    .filter(f -> key.equals(f.fieldKey()))
+                    .filter(f -> f.severity() == GuiMessageSeverity.ERROR
+                            || f.severity() == GuiMessageSeverity.WARNING)
+                    .findFirst()
+                    .ifPresentOrElse(
+                            finding -> {
+                                label.setText(finding.text());
+                                label.setVisible(true);
+                                label.setManaged(true);
+                            },
+                            () -> {
+                                label.setText("");
+                                label.setVisible(false);
+                                label.setManaged(false);
+                            });
+        }
+    }
+
+    // =========================================================================
+    // API-key origin label rendering
+    // =========================================================================
+
+    /**
+     * Updates the API-key origin labels below each provider's API-key field.
+     * <p>
+     * The display logic follows the effective-key precedence order:
+     * <ol>
+     *   <li>If the effective key comes from an environment variable, the label shows the
+     *       variable name in an informational style.</li>
+     *   <li>If the property value is filled and no environment variable overrides it, the label
+     *       is hidden.</li>
+     *   <li>If no key source is effective, the label shows a warning in the field-error style.</li>
+     * </ol>
+     * <p>
+     * The origin information is derived from the pending field findings produced by the validator,
+     * which already resolved the API-key precedence for both providers.
+     * <p>
+     * Must be called on the JavaFX Application Thread.
+     */
+    void refreshApiKeyOriginLabels() {
+        for (Map.Entry<AiProviderFamily, Label> entry : apiKeyOriginLabels.entrySet()) {
+            AiProviderFamily family = entry.getKey();
+            Label label = entry.getValue();
+            String apiKeyField = "ai.provider." + family.getIdentifier() + ".apiKey";
+
+            // Look for an INFO finding about ENV-variable origin for this provider.
+            Optional<GuiFieldFinding> envFinding = pendingFieldFindings.stream()
+                    .filter(f -> apiKeyField.equals(f.fieldKey()))
+                    .filter(f -> f.severity() == GuiMessageSeverity.INFO)
+                    .findFirst();
+
+            // Look for an ERROR/WARNING finding about missing key for this provider.
+            Optional<GuiFieldFinding> missingFinding = pendingFieldFindings.stream()
+                    .filter(f -> apiKeyField.equals(f.fieldKey()))
+                    .filter(f -> f.severity() == GuiMessageSeverity.ERROR
+                            || f.severity() == GuiMessageSeverity.WARNING)
+                    .findFirst();
+
+            if (envFinding.isPresent()) {
+                label.setText(envFinding.get().text());
+                label.setStyle(STYLE_ORIGIN_INFO);
+                label.setVisible(true);
+                label.setManaged(true);
+            } else if (missingFinding.isPresent()) {
+                label.setText(missingFinding.get().text());
+                label.setStyle(STYLE_ORIGIN_MISSING);
+                label.setVisible(true);
+                label.setManaged(true);
+            } else {
+                label.setText("");
+                label.setVisible(false);
+                label.setManaged(false);
+            }
+        }
+    }
+
+    private static final String STYLE_ORIGIN_INFO =
+            "-fx-font-size: 11px; -fx-text-fill: #1565c0; -fx-padding: 0 0 4px 0;";
+    private static final String STYLE_ORIGIN_MISSING =
+            "-fx-font-size: 11px; -fx-text-fill: #b71c1c; -fx-padding: 0 0 4px 0;";
+
     // =========================================================================
     // Path picker helpers
     // =========================================================================
@@ -1234,6 +1820,114 @@ public final class GuiConfigurationEditorWorkspace {
     // Layout helpers
     // =========================================================================
 
+    /**
+     * Creates a hidden, small red error label used for field-level validation feedback.
+     * <p>
+     * The label starts invisible and unmanaged so it consumes no layout space until a finding
+     * is attached by {@link #refreshFieldErrorLabels()}.
+     *
+     * @return a pre-configured error label; never {@code null}
+     */
+    private static Label createFieldErrorLabel() {
+        Label label = new Label();
+        label.setWrapText(true);
+        label.setStyle("-fx-font-size: 11px; -fx-text-fill: #b71c1c; -fx-padding: 0 0 4px 2px;");
+        label.setVisible(false);
+        label.setManaged(false);
+        return label;
+    }
+
+    /**
+     * Creates a hidden informational label used to display the effective API-key origin.
+     * <p>
+     * Starts invisible and unmanaged; styled and shown by {@link #refreshApiKeyOriginLabels()}.
+     *
+     * @return a pre-configured origin label; never {@code null}
+     */
+    private static Label createApiKeyOriginLabel() {
+        Label label = new Label();
+        label.setWrapText(true);
+        label.setStyle(STYLE_ORIGIN_INFO);
+        label.setVisible(false);
+        label.setManaged(false);
+        return label;
+    }
+
+    /**
+     * Builds a labelled path-field row as a {@link VBox} containing a grid row with the field
+     * and picker button, plus an optional error-slot label directly beneath.
+     * <p>
+     * The method uses an 8-pixel top padding to separate consecutive field rows visually, matching
+     * the former grid vgap behaviour.
+     *
+     * @param labelText  the row label text; must not be {@code null}
+     * @param field      the text field; must not be {@code null}
+     * @param errorLabel the field-level error label, or {@code null} for no error slot
+     * @param onPick     action invoked when the picker button is clicked; must not be {@code null}
+     * @return a VBox containing the labelled row and optional error slot
+     */
+    private static VBox buildPathFieldRow(String labelText, TextField field,
+                                          Label errorLabel, Runnable onPick) {
+        Label label = new Label(labelText);
+        Button pickButton = new Button("…");
+        pickButton.setOnAction(e -> onPick.run());
+        pickButton.setMinWidth(32);
+        HBox fieldBox = new HBox(4, field, pickButton);
+        HBox.setHgrow(field, Priority.ALWAYS);
+        fieldBox.setAlignment(Pos.CENTER_LEFT);
+
+        GridPane grid = new GridPane();
+        grid.setHgap(12);
+        grid.setVgap(0);
+        javafx.scene.layout.ColumnConstraints labelCol = new javafx.scene.layout.ColumnConstraints();
+        labelCol.setMinWidth(180);
+        labelCol.setPrefWidth(200);
+        javafx.scene.layout.ColumnConstraints fieldCol = new javafx.scene.layout.ColumnConstraints();
+        fieldCol.setFillWidth(true);
+        fieldCol.setHgrow(Priority.ALWAYS);
+        grid.getColumnConstraints().addAll(labelCol, fieldCol);
+        grid.add(label, 0, 0);
+        grid.add(fieldBox, 1, 0);
+        grid.setPadding(new Insets(4, 0, 0, 0));
+
+        VBox slot = new VBox(0, grid);
+        if (errorLabel != null) {
+            slot.getChildren().add(errorLabel);
+        }
+        return slot;
+    }
+
+    /**
+     * Builds a labelled simple-field row (no picker button) as a {@link VBox} containing a grid
+     * row with the label and text field, plus an optional error-slot label directly beneath.
+     *
+     * @param labelText  the row label text; must not be {@code null}
+     * @param field      the text field; must not be {@code null}
+     * @param errorLabel the field-level error label, or {@code null} for no error slot
+     * @return a VBox containing the labelled row and optional error slot
+     */
+    private static VBox buildSimpleFieldRow(String labelText, TextField field, Label errorLabel) {
+        GridPane grid = new GridPane();
+        grid.setHgap(12);
+        grid.setVgap(0);
+        javafx.scene.layout.ColumnConstraints labelCol = new javafx.scene.layout.ColumnConstraints();
+        labelCol.setMinWidth(180);
+        labelCol.setPrefWidth(200);
+        javafx.scene.layout.ColumnConstraints fieldCol = new javafx.scene.layout.ColumnConstraints();
+        fieldCol.setFillWidth(true);
+        fieldCol.setHgrow(Priority.ALWAYS);
+        grid.getColumnConstraints().addAll(labelCol, fieldCol);
+        grid.add(new Label(labelText), 0, 0);
+        grid.add(field, 1, 0);
+        grid.setPadding(new Insets(4, 0, 0, 0));
+
+        VBox slot = new VBox(0, grid);
+        if (errorLabel != null) {
+            slot.getChildren().add(errorLabel);
+        }
+        return slot;
+    }
+
     /**
      * Creates a text field pre-populated from the editor state that updates the state on every
      * text change.
@@ -1256,30 +1950,6 @@ public final class GuiConfigurationEditorWorkspace {
         return field;
     }
 
-    /**
-     * Adds a label, a text field and a small picker button to the given grid row.
-     * <p>
-     * The text field grows horizontally; the button stays compact.
-     *
-     * @param grid       the target grid pane
-     * @param row        the grid row index
-     * @param labelText  the row label text
-     * @param field      the text field to place
-     * @param onPick     action invoked when the picker button is clicked
-     */
-    private static void addPathRow(GridPane grid, int row, String labelText, TextField field,
-                                   Runnable onPick) {
-        Label label = new Label(labelText);
-        Button pickButton = new Button("…");
-        pickButton.setOnAction(e -> onPick.run());
-        pickButton.setMinWidth(32);
-        HBox fieldBox = new HBox(4, field, pickButton);
-        HBox.setHgrow(field, Priority.ALWAYS);
-        fieldBox.setAlignment(Pos.CENTER_LEFT);
-        grid.add(label, 0, row);
-        grid.add(fieldBox, 1, row);
-    }
-
     /**
      * Adds a label and a text field (without a picker button) to the given grid row.
      *
diff --git a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiModelCatalogCoordinator.java b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiModelCatalogCoordinator.java
new file mode 100644
index 0000000..9c915c0
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiModelCatalogCoordinator.java
@@ -0,0 +1,277 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Function;
+
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiMessageEntry;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiMessageSeverity;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiModelFieldContainer;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiModelSource;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiProviderConfigurationState;
+import de.gecheckt.pdf.umbenenner.application.config.provider.AiProviderFamily;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.AiModelCatalogPort;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogRequest;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult;
+import javafx.application.Platform;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+
+/**
+ * Coordinates asynchronous model catalogue retrieval for the GUI provider section.
+ * <p>
+ * This coordinator is responsible for:
+ * <ul>
+ *   <li>Triggering a background HTTP call via {@link AiModelCatalogPort} on a dedicated
+ *       daemon thread named {@code gui-model-catalog}.</li>
+ *   <li>Returning the result to the JavaFX Application Thread via {@code Platform.runLater}.</li>
+ *   <li>Updating the per-provider {@link GuiModelFieldContainer} to show either a
+ *       non-editable {@code ComboBox} (success) or a manual text field (all other cases).</li>
+ *   <li>Appending a {@link GuiMessageEntry} to the supplied pending-messages list for each
+ *       completed retrieval attempt, so later GUI layers can display the result.</li>
+ * </ul>
+ * <p>
+ * The worker thread factory is injectable so tests can supply a synchronous or latch-guarded
+ * executor without spinning a real OS thread.
+ * <p>
+ * This class is not thread-safe by itself. All methods intended to mutate GUI state must be
+ * called on the JavaFX Application Thread. Background threads only interact through
+ * {@code Platform.runLater}.
+ */
+public final class GuiModelCatalogCoordinator {
+
+    private static final Logger LOG = LogManager.getLogger(GuiModelCatalogCoordinator.class);
+
+    /** Default timeout used when no timeout is configured in the provider state. */
+    static final int DEFAULT_TIMEOUT_SECONDS = 10;
+
+    private final AiModelCatalogPort modelCatalogPort;
+    private final List<GuiMessageEntry> pendingMessages;
+
+    /**
+     * Factory for the background worker thread. Package-private to allow test substitution.
+     * The default creates a daemon thread named {@code gui-model-catalog}.
+     */
+    Function<Runnable, Thread> modelCatalogThreadFactory;
+
+    /** Per-provider field containers; populated by the workspace when it builds provider blocks. */
+    private final Map<AiProviderFamily, GuiModelFieldContainer> fieldContainers =
+            new ConcurrentHashMap<>();
+
+    /**
+     * Consumer that delivers the retrieval result. In production this wraps the call in
+     * {@code Platform.runLater}. In tests it can be replaced with a direct call so the result
+     * is applied immediately on the worker thread without needing an FX queue drain.
+     * Package-private to allow test substitution.
+     */
+    java.util.function.Consumer<Runnable> resultDelivery = Platform::runLater;
+
+    /**
+     * Optional callback invoked on the JavaFX Application Thread after each retrieval result has
+     * been applied. The workspace uses this hook to refresh the central message area and field-error
+     * labels without coupling the coordinator to the workspace implementation.
+     * Package-private to allow substitution in tests.
+     */
+    Runnable postResultCallback = () -> { };
+
+    /**
+     * Creates a coordinator backed by the given catalogue port and shared message list.
+     *
+     * @param modelCatalogPort port used for background HTTP calls; must not be {@code null}
+     * @param pendingMessages  mutable list to append result messages to; must not be {@code null}
+     */
+    public GuiModelCatalogCoordinator(AiModelCatalogPort modelCatalogPort,
+                                      List<GuiMessageEntry> pendingMessages) {
+        this.modelCatalogPort = Objects.requireNonNull(modelCatalogPort,
+                "modelCatalogPort must not be null");
+        this.pendingMessages = Objects.requireNonNull(pendingMessages,
+                "pendingMessages must not be null");
+        this.modelCatalogThreadFactory = task -> {
+            Thread t = new Thread(task, "gui-model-catalog");
+            t.setDaemon(true);
+            return t;
+        };
+    }
+
+    /**
+     * Registers a {@link GuiModelFieldContainer} for the given provider family.
+     * <p>
+     * Must be called on the JavaFX Application Thread before the first retrieval is triggered.
+     *
+     * @param family    the provider family this container belongs to; must not be {@code null}
+     * @param container the container to register; must not be {@code null}
+     */
+    public void registerFieldContainer(AiProviderFamily family, GuiModelFieldContainer container) {
+        Objects.requireNonNull(family, "family must not be null");
+        Objects.requireNonNull(container, "container must not be null");
+        fieldContainers.put(family, container);
+    }
+
+    /**
+     * Triggers an asynchronous model catalogue retrieval for the given provider family.
+     * <p>
+     * The retrieval is performed on a background worker thread. The result is delivered back
+     * to the JavaFX Application Thread via {@code Platform.runLater}. The registered
+     * {@link GuiModelFieldContainer} for the provider is updated accordingly, and a
+     * {@link GuiMessageEntry} is appended to the pending-messages list.
+     * <p>
+     * If no field container is registered for the provider, the call is a no-op.
+     * <p>
+     * Must be called on the JavaFX Application Thread.
+     *
+     * @param family        the provider family to retrieve models for; must not be {@code null}
+     * @param providerState the current editor state for the provider; must not be {@code null}
+     */
+    public void triggerModelRetrieval(AiProviderFamily family,
+                                      GuiProviderConfigurationState providerState) {
+        Objects.requireNonNull(family, "family must not be null");
+        Objects.requireNonNull(providerState, "providerState must not be null");
+
+        GuiModelFieldContainer container = fieldContainers.get(family);
+        if (container == null) {
+            LOG.debug("GUI-Modellabruf: Kein Feld-Container für Provider '{}' registriert – übersprungen.",
+                    family.getIdentifier());
+            return;
+        }
+
+        // Capture the current manual value before starting the background call.
+        String previousManualValue = container.currentModelValue();
+
+        // Build the request from the current editor state.
+        ModelCatalogRequest request = buildRequest(family, providerState);
+
+        LOG.info("GUI-Modellabruf: Modelllistenabruf für Provider '{}' gestartet.",
+                family.getIdentifier());
+
+        Runnable task = () -> {
+            ModelCatalogResult result = modelCatalogPort.fetchAvailableModels(request);
+            resultDelivery.accept(() -> {
+                applyResult(family, container, result, previousManualValue);
+                postResultCallback.run();
+            });
+        };
+
+        Thread worker = modelCatalogThreadFactory.apply(task);
+        worker.start();
+    }
+
+    /**
+     * Applies the result of a completed model catalogue retrieval to the field container and
+     * appends a message entry to the pending-messages list.
+     * <p>
+     * Must only be called on the JavaFX Application Thread (via {@code Platform.runLater}).
+     *
+     * @param family              the provider family that was queried; must not be {@code null}
+     * @param container           the field container to update; must not be {@code null}
+     * @param result              the retrieval result; must not be {@code null}
+     * @param previousManualValue the model value that was in the text field before the call
+     */
+    private void applyResult(AiProviderFamily family,
+                             GuiModelFieldContainer container,
+                             ModelCatalogResult result,
+                             String previousManualValue) {
+        // Remove any previous message entries from an earlier retrieval so messages do not
+        // accumulate across repeated triggers of the same retrieval action.
+        pendingMessages.removeIf(msg -> "Modellabruf".equals(msg.source().orElse("")));
+
+        String displayName = displayNameFor(family);
+
+        switch (result) {
+            case ModelCatalogResult.Success success -> {
+                List<String> models = success.models();
+                container.applyModelList(models, previousManualValue);
+                String message = "Modellliste für " + displayName + " geladen ("
+                        + models.size() + " " + (models.size() == 1 ? "Eintrag" : "Einträge") + ").";
+                pendingMessages.add(GuiMessageEntry.of(GuiMessageSeverity.INFO, message, "Modellabruf"));
+                LOG.info("GUI-Modellabruf: {} (Provider: {})", message, family.getIdentifier());
+            }
+            case ModelCatalogResult.EmptyList emptyList -> {
+                container.applyManualFallback(GuiModelSource.LIST_UNAVAILABLE_MANUAL_INPUT);
+                String message = "Provider " + displayName
+                        + " liefert aktuell keine Modelle. Manuelle Eingabe aktiv.";
+                pendingMessages.add(GuiMessageEntry.of(GuiMessageSeverity.HINT, message, "Modellabruf"));
+                LOG.info("GUI-Modellabruf: {} (Provider: {})", message, family.getIdentifier());
+            }
+            case ModelCatalogResult.IncompleteConfiguration incomplete -> {
+                container.applyManualFallback(GuiModelSource.LIST_UNAVAILABLE_MANUAL_INPUT);
+                String message = "Modellliste nicht abrufbar: " + incomplete.missingReason()
+                        + ". Manuelle Eingabe aktiv.";
+                pendingMessages.add(GuiMessageEntry.of(GuiMessageSeverity.WARNING, message, "Modellabruf"));
+                LOG.info("GUI-Modellabruf: {} (Provider: {})", message, family.getIdentifier());
+            }
+            case ModelCatalogResult.TechnicalFailure failure -> {
+                container.applyManualFallback(GuiModelSource.LIST_FAILED_MANUAL_INPUT);
+                String message = "Modellliste nicht abrufbar (" + failure.errorCategory()
+                        + "). Manuelle Eingabe aktiv.";
+                pendingMessages.add(GuiMessageEntry.of(GuiMessageSeverity.ERROR, message, "Modellabruf"));
+                LOG.warn("GUI-Modellabruf: {} Detail: {} (Provider: {})",
+                        message, failure.errorDetail(), family.getIdentifier());
+            }
+        }
+    }
+
+    /**
+     * Builds a {@link ModelCatalogRequest} from the current provider editor state.
+     * <p>
+     * Missing or blank values are passed as {@code Optional.empty()} so the adapter can apply
+     * its own defaults or return {@link ModelCatalogResult.IncompleteConfiguration} if required
+     * values are absent.
+     *
+     * @param family        the target provider family; must not be {@code null}
+     * @param providerState the current provider editor state; must not be {@code null}
+     * @return a new request; never {@code null}
+     */
+    private static ModelCatalogRequest buildRequest(AiProviderFamily family,
+                                                    GuiProviderConfigurationState providerState) {
+        Optional<String> baseUrl = Optional.ofNullable(providerState.baseUrl())
+                .filter(s -> !s.isBlank());
+        Optional<String> apiKey = Optional.ofNullable(providerState.apiKey())
+                .map(keyState -> keyState.propertyValue())
+                .filter(s -> !s.isBlank());
+
+        int timeout = DEFAULT_TIMEOUT_SECONDS;
+        String timeoutStr = providerState.timeoutSeconds();
+        if (timeoutStr != null && !timeoutStr.isBlank()) {
+            try {
+                int parsed = Integer.parseInt(timeoutStr.trim());
+                if (parsed > 0) {
+                    timeout = parsed;
+                }
+            } catch (NumberFormatException ignored) {
+                // Use default.
+            }
+        }
+
+        return new ModelCatalogRequest(family.getIdentifier(), baseUrl, apiKey, timeout);
+    }
+
+    /**
+     * Returns a human-readable display name for the given provider family.
+     *
+     * @param family the provider family; must not be {@code null}
+     * @return the display name; never {@code null}
+     */
+    private static String displayNameFor(AiProviderFamily family) {
+        return switch (family) {
+            case CLAUDE -> "Claude";
+            case OPENAI_COMPATIBLE -> "OpenAI-kompatibel";
+        };
+    }
+
+    /**
+     * Returns an unmodifiable snapshot of the pending messages collected so far.
+     * <p>
+     * This method is intended for tests that need to inspect the message list after
+     * a retrieval completes.
+     *
+     * @return unmodifiable list of pending messages; never {@code null}
+     */
+    public List<GuiMessageEntry> pendingMessagesSnapshot() {
+        return List.copyOf(pendingMessages);
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiStartupContext.java b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiStartupContext.java
index 6a0e75b..572280c 100644
--- a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiStartupContext.java
+++ b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiStartupContext.java
@@ -5,26 +5,40 @@ import java.util.Optional;
 
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationEditorState;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationEditorStateFactory;
+import de.gecheckt.pdf.umbenenner.application.config.provider.AiProviderFamily;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.AiModelCatalogPort;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor;
+import de.gecheckt.pdf.umbenenner.application.validation.editor.ApiKeyResolutionPort;
 
 /**
  * Immutable startup data for the GUI adapter.
  * <p>
- * Carries the initial editor state, the optional startup notice, the file-loading callback
- * and the file-writing callback that the workspace uses for native save actions.
+ * Carries the initial editor state, the optional startup notice, the file-loading callback,
+ * the file-writing callback that the workspace uses for native save actions, the
+ * {@link AiModelCatalogPort} used to retrieve available AI model lists on demand, and the
+ * {@link ApiKeyResolutionPort} used by the editor validation to determine the effective
+ * API key provenance from environment variables.
+ * <p>
+ * All ports are supplied by Bootstrap so that the GUI adapter does not need to know about
+ * provider-specific HTTP details or adapter wiring.
  */
 public record GuiStartupContext(
         GuiConfigurationEditorState initialState,
         Optional<String> startupNotice,
         GuiConfigurationFileLoader configurationFileLoader,
-        GuiConfigurationFileWriter configurationFileWriter) {
+        GuiConfigurationFileWriter configurationFileWriter,
+        AiModelCatalogPort modelCatalogPort,
+        ApiKeyResolutionPort apiKeyResolutionPort) {
 
     /**
      * Creates a startup context.
      *
-     * @param initialState initial editor state; must not be {@code null}
-     * @param startupNotice optional startup notice; {@code null} becomes empty
+     * @param initialState            initial editor state; must not be {@code null}
+     * @param startupNotice           optional startup notice; {@code null} becomes empty
      * @param configurationFileLoader file-loading callback; must not be {@code null}
      * @param configurationFileWriter file-writing callback; must not be {@code null}
+     * @param modelCatalogPort        port for retrieving AI model lists; must not be {@code null}
+     * @param apiKeyResolutionPort    port for resolving API key provenance; must not be {@code null}
      */
     public GuiStartupContext {
         initialState = Objects.requireNonNull(initialState, "initialState must not be null");
@@ -33,10 +47,20 @@ public record GuiStartupContext(
                 "configurationFileLoader must not be null");
         configurationFileWriter = Objects.requireNonNull(configurationFileWriter,
                 "configurationFileWriter must not be null");
+        modelCatalogPort = Objects.requireNonNull(modelCatalogPort,
+                "modelCatalogPort must not be null");
+        apiKeyResolutionPort = Objects.requireNonNull(apiKeyResolutionPort,
+                "apiKeyResolutionPort must not be null");
     }
 
     /**
-     * Creates a blank startup context with no loader or writer side effects.
+     * Creates a blank startup context with no loader or writer side effects, a no-op model
+     * catalogue port, and a no-op API key resolution port.
+     * <p>
+     * The no-op model catalogue port always returns {@code IncompleteConfiguration}.
+     * The no-op API key resolution port always returns {@code ABSENT}.
+     * This is safe for environments where no Bootstrap wiring is present, such as isolated
+     * GUI tests.
      *
      * @param startupNotice optional startup notice; {@code null} becomes empty
      * @return a startup context for the unloaded editor start
@@ -46,6 +70,11 @@ public record GuiStartupContext(
                 GuiConfigurationEditorStateFactory.createBlankStartState(),
                 startupNotice,
                 configFilePath -> GuiConfigurationEditorStateFactory.createBlankStartState(),
-                (values, path) -> GuiConfigurationSaveResult.saved(path));
+                (values, path) -> GuiConfigurationSaveResult.saved(path),
+                request -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog
+                        .ModelCatalogResult.IncompleteConfiguration(
+                                request.providerIdentifier(),
+                                "Kein Modellkatalog in diesem Startkontext verfügbar."),
+                (family, propertyValue) -> EffectiveApiKeyDescriptor.absent());
     }
 }
diff --git a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/AiProviderFamilyStringConverter.java b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/AiProviderFamilyStringConverter.java
new file mode 100644
index 0000000..461df11
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/AiProviderFamilyStringConverter.java
@@ -0,0 +1,63 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import de.gecheckt.pdf.umbenenner.application.config.provider.AiProviderFamily;
+import javafx.util.StringConverter;
+
+/**
+ * A JavaFX {@link StringConverter} that maps {@link AiProviderFamily} constants to
+ * German display labels and back.
+ * <p>
+ * Used by the provider selection {@code ComboBox} to show human-readable German names
+ * while keeping the underlying model type-safe. The reverse conversion
+ * ({@link #fromString(String)}) supports the same label strings produced by
+ * {@link #toString(AiProviderFamily)} so that a ComboBox configured as non-editable
+ * can still convert its selected text back to the enum constant when needed.
+ * <p>
+ * Returns {@code null} for inputs that do not match any known constant to signal an
+ * unrecognised display label.
+ */
+public final class AiProviderFamilyStringConverter extends StringConverter<AiProviderFamily> {
+
+    /**
+     * Creates a new converter instance.
+     */
+    public AiProviderFamilyStringConverter() {
+        // Default constructor.
+    }
+
+    /**
+     * Returns the German display label for the given provider family.
+     *
+     * @param family the provider family to convert; may be {@code null}
+     * @return the German display label, or an empty string when {@code family} is {@code null}
+     */
+    @Override
+    public String toString(AiProviderFamily family) {
+        if (family == null) {
+            return "";
+        }
+        return switch (family) {
+            case CLAUDE -> "Claude";
+            case OPENAI_COMPATIBLE -> "OpenAI-kompatibel";
+        };
+    }
+
+    /**
+     * Resolves a German display label back to its {@link AiProviderFamily} constant.
+     *
+     * @param label the display label as produced by {@link #toString(AiProviderFamily)};
+     *              may be {@code null}
+     * @return the matching constant, or {@code null} when the label is not recognised
+     */
+    @Override
+    public AiProviderFamily fromString(String label) {
+        if (label == null) {
+            return null;
+        }
+        return switch (label) {
+            case "Claude" -> AiProviderFamily.CLAUDE;
+            case "OpenAI-kompatibel" -> AiProviderFamily.OPENAI_COMPATIBLE;
+            default -> null;
+        };
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiEditorValidationResult.java b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiEditorValidationResult.java
new file mode 100644
index 0000000..058cfb7
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiEditorValidationResult.java
@@ -0,0 +1,93 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import java.time.Instant;
+import java.util.List;
+import java.util.Objects;
+
+/**
+ * Represents the result of validating the current editor state in the GUI configuration editor.
+ * <p>
+ * Each validation run produces one immutable result containing all findings split into two
+ * complementary views:
+ * <ul>
+ *   <li>{@code messages} – a consolidated list of {@link GuiMessageEntry} objects that feed
+ *       the central message area.</li>
+ *   <li>{@code fieldFindings} – field-specific {@link GuiFieldFinding} objects that are
+ *       rendered directly below the affected input fields.</li>
+ * </ul>
+ * <p>
+ * A single root cause may appear in both lists: once as a central message (with full context)
+ * and once as a compact field finding (with a short, field-specific description).
+ * <p>
+ * The {@code evaluatedAt} timestamp records when the validation ran; the GUI may use it to
+ * determine whether a displayed result is still current.
+ * <p>
+ * This record contains no JavaFX references and can be created and inspected on any thread.
+ *
+ * @param messages       consolidated list of message entries for the central message area;
+ *                       never {@code null}
+ * @param fieldFindings  list of field-level findings; never {@code null}
+ * @param evaluatedAt    instant at which the validation was performed; never {@code null}
+ */
+public record GuiEditorValidationResult(
+        List<GuiMessageEntry> messages,
+        List<GuiFieldFinding> fieldFindings,
+        Instant evaluatedAt) {
+
+    /**
+     * Creates a new validation result.
+     *
+     * @param messages      central message entries; must not be {@code null}
+     * @param fieldFindings field-level findings; must not be {@code null}
+     * @param evaluatedAt   validation timestamp; must not be {@code null}
+     * @throws NullPointerException if any parameter is {@code null}
+     */
+    public GuiEditorValidationResult {
+        Objects.requireNonNull(messages, "messages must not be null");
+        Objects.requireNonNull(fieldFindings, "fieldFindings must not be null");
+        Objects.requireNonNull(evaluatedAt, "evaluatedAt must not be null");
+        messages = List.copyOf(messages);
+        fieldFindings = List.copyOf(fieldFindings);
+    }
+
+    /**
+     * Returns an empty validation result representing the state before any validation has run.
+     * <p>
+     * Callers must not interpret an empty result as "no errors found"; they should wait for
+     * a non-empty result from the first actual validation run.
+     *
+     * @return an empty result with the current instant as timestamp; never {@code null}
+     */
+    public static GuiEditorValidationResult empty() {
+        return new GuiEditorValidationResult(List.of(), List.of(), Instant.now());
+    }
+
+    /**
+     * Returns {@code true} when at least one message or field finding has severity
+     * {@link GuiMessageSeverity#ERROR}.
+     * <p>
+     * A result with errors indicates that the current editor state is not operational and
+     * should not be relied upon to start a processing run without correction.
+     *
+     * @return {@code true} when at least one error is present
+     */
+    public boolean hasErrors() {
+        boolean messageError = messages.stream()
+                .anyMatch(m -> m.severity() == GuiMessageSeverity.ERROR);
+        boolean fieldError = fieldFindings.stream()
+                .anyMatch(f -> f.severity() == GuiMessageSeverity.ERROR);
+        return messageError || fieldError;
+    }
+
+    /**
+     * Returns {@code true} when the findings list contains at least one finding for the
+     * requested field key, regardless of severity.
+     *
+     * @param fieldKey the property key to look up; must not be {@code null}
+     * @return {@code true} when at least one finding refers to the requested field
+     */
+    public boolean hasFieldFindingFor(String fieldKey) {
+        Objects.requireNonNull(fieldKey, "fieldKey must not be null");
+        return fieldFindings.stream().anyMatch(f -> f.fieldKey().equals(fieldKey));
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiFieldFinding.java b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiFieldFinding.java
new file mode 100644
index 0000000..d3692bf
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiFieldFinding.java
@@ -0,0 +1,68 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import java.util.Objects;
+
+/**
+ * Represents a field-level validation finding that is displayed directly below the affected
+ * input field in the GUI configuration editor.
+ * <p>
+ * Field-level findings complement the central message area: the central area shows all findings
+ * in a consolidated list while this type carries the finding directly to the specific field it
+ * relates to, making it easier for the user to identify and correct the problem.
+ * <p>
+ * The {@code fieldKey} uses the property key as defined in the {@code .properties} file
+ * (e.g., {@code "source.folder"}, {@code "ai.provider.openai-compatible.apiKey"}).
+ * Using the property key as the field identifier keeps the validation model stable and independent
+ * of GUI layout changes.
+ * <p>
+ * Field-level findings are always rendered as small red German-language text directly beneath
+ * the affected control. Findings with severity {@link GuiMessageSeverity#INFO} or
+ * {@link GuiMessageSeverity#HINT} may also be shown field-near when the context is helpful.
+ * <p>
+ * This record contains no JavaFX references and is safe to create on any thread.
+ *
+ * @param fieldKey the property key identifying the affected configuration field; never {@code null}
+ * @param severity the severity of this finding; never {@code null}
+ * @param text     short, German-language description of the problem; never {@code null}
+ */
+public record GuiFieldFinding(
+        String fieldKey,
+        GuiMessageSeverity severity,
+        String text) {
+
+    /**
+     * Creates a new field-level finding.
+     *
+     * @param fieldKey property key of the affected field; must not be {@code null}
+     * @param severity severity of the finding; must not be {@code null}
+     * @param text     German-language problem description; must not be {@code null}
+     * @throws NullPointerException if any parameter is {@code null}
+     */
+    public GuiFieldFinding {
+        Objects.requireNonNull(fieldKey, "fieldKey must not be null");
+        Objects.requireNonNull(severity, "severity must not be null");
+        Objects.requireNonNull(text, "text must not be null");
+    }
+
+    /**
+     * Creates an error-severity field finding.
+     *
+     * @param fieldKey property key of the affected field; must not be {@code null}
+     * @param text     German-language problem description; must not be {@code null}
+     * @return a new finding with severity {@link GuiMessageSeverity#ERROR}
+     */
+    public static GuiFieldFinding error(String fieldKey, String text) {
+        return new GuiFieldFinding(fieldKey, GuiMessageSeverity.ERROR, text);
+    }
+
+    /**
+     * Creates a warning-severity field finding.
+     *
+     * @param fieldKey property key of the affected field; must not be {@code null}
+     * @param text     German-language problem description; must not be {@code null}
+     * @return a new finding with severity {@link GuiMessageSeverity#WARNING}
+     */
+    public static GuiFieldFinding warning(String fieldKey, String text) {
+        return new GuiFieldFinding(fieldKey, GuiMessageSeverity.WARNING, text);
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiManualModelEntry.java b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiManualModelEntry.java
new file mode 100644
index 0000000..ae847b4
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiManualModelEntry.java
@@ -0,0 +1,45 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import java.util.Objects;
+
+/**
+ * Represents the model identifier entered manually by the user when no remote model list
+ * is available for the active provider.
+ * <p>
+ * This record captures both the provider context and the user-supplied model name so that
+ * later GUI layers can decide whether the value is still applicable after a provider change
+ * or a successful remote list retrieval.
+ * <p>
+ * A manually entered model name is discarded when a remote model list is subsequently loaded
+ * and the previously entered value does not appear in that list.
+ *
+ * @param providerIdentifier identifier of the provider for which the model was entered;
+ *                           never {@code null}
+ * @param modelName          model identifier as typed by the user; never {@code null},
+ *                           but may be blank when the user has not yet entered anything
+ */
+public record GuiManualModelEntry(
+        String providerIdentifier,
+        String modelName) {
+
+    /**
+     * Creates a new manual model entry.
+     *
+     * @param providerIdentifier identifier of the provider; must not be {@code null}
+     * @param modelName          model name as entered by the user; must not be {@code null}
+     * @throws NullPointerException if any parameter is {@code null}
+     */
+    public GuiManualModelEntry {
+        Objects.requireNonNull(providerIdentifier, "providerIdentifier must not be null");
+        Objects.requireNonNull(modelName, "modelName must not be null");
+    }
+
+    /**
+     * Returns whether the model name is non-blank, i.e. whether the user has entered something.
+     *
+     * @return {@code true} when the model name contains at least one non-whitespace character
+     */
+    public boolean hasModelName() {
+        return !modelName.isBlank();
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiMessageEntry.java b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiMessageEntry.java
new file mode 100644
index 0000000..a46cd95
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiMessageEntry.java
@@ -0,0 +1,68 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import java.time.Instant;
+import java.util.Objects;
+import java.util.Optional;
+
+/**
+ * Represents a single entry in the central message area of the GUI configuration editor.
+ * <p>
+ * Each entry carries a severity level, the message text, an optional source label that
+ * identifies the subsystem that produced the message (e.g., "Modellabruf", "Validierung"),
+ * and a timestamp. The GUI renders the {@link GuiMessageSeverity#getPrefixLabel() prefix} of
+ * the severity in colour while the message text itself remains black.
+ * <p>
+ * Instances are immutable and contain no JavaFX references; they are safe to create on
+ * background threads and pass to the JavaFX Application Thread via {@code Platform.runLater}.
+ *
+ * @param severity  the severity of this message; never {@code null}
+ * @param text      the message text; never {@code null}
+ * @param source    optional label identifying the origin subsystem; empty when not applicable
+ * @param timestamp the instant at which the message was created; never {@code null}
+ */
+public record GuiMessageEntry(
+        GuiMessageSeverity severity,
+        String text,
+        Optional<String> source,
+        Instant timestamp) {
+
+    /**
+     * Creates a new message entry.
+     *
+     * @param severity  severity level; must not be {@code null}
+     * @param text      message text; must not be {@code null}
+     * @param source    optional source label; {@code null} is treated as {@link Optional#empty()}
+     * @param timestamp creation timestamp; must not be {@code null}
+     * @throws NullPointerException if {@code severity}, {@code text}, or {@code timestamp} is {@code null}
+     */
+    public GuiMessageEntry {
+        Objects.requireNonNull(severity, "severity must not be null");
+        Objects.requireNonNull(text, "text must not be null");
+        Objects.requireNonNull(timestamp, "timestamp must not be null");
+        source = source == null ? Optional.empty() : source;
+    }
+
+    /**
+     * Creates a message entry without a source label, using the current instant as timestamp.
+     *
+     * @param severity severity level; must not be {@code null}
+     * @param text     message text; must not be {@code null}
+     * @return a new entry; never {@code null}
+     */
+    public static GuiMessageEntry of(GuiMessageSeverity severity, String text) {
+        return new GuiMessageEntry(severity, text, Optional.empty(), Instant.now());
+    }
+
+    /**
+     * Creates a message entry with a source label, using the current instant as timestamp.
+     *
+     * @param severity severity level; must not be {@code null}
+     * @param text     message text; must not be {@code null}
+     * @param source   source subsystem label; must not be {@code null}
+     * @return a new entry; never {@code null}
+     */
+    public static GuiMessageEntry of(GuiMessageSeverity severity, String text, String source) {
+        Objects.requireNonNull(source, "source must not be null");
+        return new GuiMessageEntry(severity, text, Optional.of(source), Instant.now());
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiMessageSeverity.java b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiMessageSeverity.java
new file mode 100644
index 0000000..6863463
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiMessageSeverity.java
@@ -0,0 +1,71 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+/**
+ * Defines the four fixed severity levels for messages displayed in the central message area
+ * of the GUI configuration editor.
+ * <p>
+ * Each level carries a German-language prefix string that is displayed in colour at the start
+ * of each message line. The remainder of the message text is always rendered in black,
+ * regardless of severity.
+ * <p>
+ * The colour hints in this enum are expressed as CSS colour strings to avoid a compile-time
+ * dependency on JavaFX. Rendering code in the GUI layer must convert the hint to a
+ * {@code javafx.scene.paint.Color} or equivalent.
+ * <p>
+ * Severity levels ordered from least to most critical:
+ * <ol>
+ *   <li>{@link #INFO}</li>
+ *   <li>{@link #HINT}</li>
+ *   <li>{@link #WARNING}</li>
+ *   <li>{@link #ERROR}</li>
+ * </ol>
+ * <p>
+ * This enum contains no JavaFX references and is safe to use in unit-tested view-model code.
+ */
+public enum GuiMessageSeverity {
+
+    /** Neutral informational message, no action required. */
+    INFO("Info:", "#1565c0"),
+
+    /** Helpful hint that the user may want to act on. */
+    HINT("Hinweis:", "#558b2f"),
+
+    /** Configuration value is technically acceptable but risky or unusual. */
+    WARNING("Warnung:", "#e65100"),
+
+    /** Configuration value is invalid or the state is not operational. */
+    ERROR("Fehler:", "#b71c1c");
+
+    private final String prefixLabel;
+    private final String prefixCssColour;
+
+    GuiMessageSeverity(String prefixLabel, String prefixCssColour) {
+        this.prefixLabel = prefixLabel;
+        this.prefixCssColour = prefixCssColour;
+    }
+
+    /**
+     * Returns the German-language prefix label shown at the start of each message line of this severity.
+     * <p>
+     * Only the prefix is rendered in colour; the remaining message text is always black.
+     *
+     * @return the prefix label; never {@code null}
+     */
+    public String getPrefixLabel() {
+        return prefixLabel;
+    }
+
+    /**
+     * Returns a CSS colour string hint that the GUI layer uses to render the prefix in the
+     * appropriate colour.
+     * <p>
+     * The returned value is a CSS hex colour (e.g., {@code "#b71c1c"}) that can be passed to
+     * {@code Color.web()} in JavaFX. The GUI layer is responsible for this conversion; this
+     * enum itself contains no JavaFX dependency.
+     *
+     * @return a CSS colour hint string; never {@code null}
+     */
+    public String getPrefixCssColour() {
+        return prefixCssColour;
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiModelFieldContainer.java b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiModelFieldContainer.java
new file mode 100644
index 0000000..590d5fd
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiModelFieldContainer.java
@@ -0,0 +1,190 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import java.util.List;
+import java.util.Objects;
+import java.util.function.Consumer;
+
+import javafx.scene.Node;
+import javafx.scene.control.ComboBox;
+import javafx.scene.control.TextField;
+import javafx.scene.layout.StackPane;
+
+/**
+ * A container that switches between a non-editable {@link ComboBox} and a manual {@link TextField}
+ * for model identifier input, depending on the current {@link GuiModelSource}.
+ * <p>
+ * When the model source is {@link GuiModelSource#LIST_REMOTE_SUCCESS}, a non-editable
+ * {@code ComboBox} is shown, pre-populated with the remote list and with the first model
+ * pre-selected. In all other cases (including {@link GuiModelSource#NOT_YET_LOADED}) the
+ * manual text field is shown, which may be empty or disabled depending on the source state.
+ * <p>
+ * Exactly one child is {@code visible} and {@code managed} at any time. The other child is
+ * kept in the scene graph with both flags set to {@code false} so that no blank space appears.
+ * <p>
+ * This class contains JavaFX references and must only be used on the JavaFX Application Thread.
+ */
+public final class GuiModelFieldContainer extends StackPane {
+
+    private final ComboBox<String> comboBox;
+    private final TextField textField;
+    private final Consumer<String> onModelChange;
+
+    private GuiModelSource currentSource;
+
+    /**
+     * Guard flag that suppresses the change callback while the text field value is being set
+     * programmatically via {@link #setTextFieldValue(String)}. The callback must still fire on
+     * genuine user edits, so the guard is scoped tightly around the programmatic write only.
+     */
+    private boolean programmaticTextFieldSet = false;
+
+    /**
+     * Creates a new model field container.
+     *
+     * @param initialModelValue the initial model text shown in the text field; may be blank
+     * @param onModelChange     callback invoked on every model-value change; must not be {@code null}
+     */
+    public GuiModelFieldContainer(String initialModelValue, Consumer<String> onModelChange) {
+        this.onModelChange = Objects.requireNonNull(onModelChange, "onModelChange must not be null");
+        this.currentSource = GuiModelSource.NOT_YET_LOADED;
+
+        this.textField = new TextField(initialModelValue == null ? "" : initialModelValue);
+        this.textField.textProperty().addListener((obs, oldText, newText) -> {
+            if (!programmaticTextFieldSet && !newText.equals(oldText)) {
+                onModelChange.accept(newText);
+            }
+        });
+
+        this.comboBox = new ComboBox<>();
+        this.comboBox.setEditable(false);
+        this.comboBox.valueProperty().addListener((obs, oldVal, newVal) -> {
+            if (newVal != null && !newVal.equals(oldVal)) {
+                onModelChange.accept(newVal);
+            }
+        });
+
+        // Initial state: show text field (NOT_YET_LOADED → manual input)
+        applyVisibility(false);
+        getChildren().addAll(comboBox, textField);
+    }
+
+    /**
+     * Returns the currently displayed model value.
+     * <p>
+     * When the {@code ComboBox} is active, returns the selected item. When the text field
+     * is active, returns the text field content. Never returns {@code null}.
+     *
+     * @return the current model value; never {@code null}
+     */
+    public String currentModelValue() {
+        if (currentSource == GuiModelSource.LIST_REMOTE_SUCCESS) {
+            String val = comboBox.getValue();
+            return val == null ? "" : val;
+        }
+        return textField.getText() == null ? "" : textField.getText();
+    }
+
+    /**
+     * Returns the current model source state.
+     *
+     * @return the current {@link GuiModelSource}; never {@code null}
+     */
+    public GuiModelSource currentSource() {
+        return currentSource;
+    }
+
+    /**
+     * Applies a successful model list and switches to the non-editable {@link ComboBox}.
+     * <p>
+     * If the previously active manual text value is present in the new list it is kept as the
+     * selection; otherwise the first model in the list is pre-selected and the former manual
+     * value is discarded.
+     * <p>
+     * Must be called on the JavaFX Application Thread.
+     *
+     * @param models           non-empty list of model identifiers; must not be {@code null} or empty
+     * @param previousManualValue the model text that was in the text field before this call;
+     *                            used to decide whether to preserve the selection
+     * @throws IllegalArgumentException if {@code models} is empty
+     */
+    public void applyModelList(List<String> models, String previousManualValue) {
+        Objects.requireNonNull(models, "models must not be null");
+        if (models.isEmpty()) {
+            throw new IllegalArgumentException("models must not be empty");
+        }
+
+        comboBox.getItems().setAll(models);
+
+        // Preserve the previous value only when it appears in the new list.
+        String previous = previousManualValue == null ? "" : previousManualValue;
+        if (!previous.isBlank() && models.contains(previous)) {
+            comboBox.setValue(previous);
+        } else {
+            comboBox.setValue(models.get(0));
+        }
+
+        currentSource = GuiModelSource.LIST_REMOTE_SUCCESS;
+        applyVisibility(true);
+        // Notify the callback about the newly selected value.
+        String selected = comboBox.getValue();
+        if (selected != null) {
+            onModelChange.accept(selected);
+        }
+    }
+
+    /**
+     * Switches to the manual text field with the given fallback source state.
+     * <p>
+     * The text field retains whatever value it currently holds (or the value set programmatically
+     * via {@link #setTextFieldValue(String)}). Must be called on the JavaFX Application Thread.
+     *
+     * @param source the non-success source state; must not be {@link GuiModelSource#LIST_REMOTE_SUCCESS}
+     */
+    public void applyManualFallback(GuiModelSource source) {
+        Objects.requireNonNull(source, "source must not be null");
+        if (source == GuiModelSource.LIST_REMOTE_SUCCESS) {
+            throw new IllegalArgumentException(
+                    "applyManualFallback must not be called with LIST_REMOTE_SUCCESS");
+        }
+        currentSource = source;
+        applyVisibility(false);
+    }
+
+    /**
+     * Programmatically sets the text field value without triggering the change callback.
+     * <p>
+     * Useful for restoring a saved model value after a provider switch. Must be called on the
+     * JavaFX Application Thread.
+     *
+     * @param value the new text field value; {@code null} is treated as an empty string
+     */
+    public void setTextFieldValue(String value) {
+        programmaticTextFieldSet = true;
+        try {
+            textField.setText(value == null ? "" : value);
+        } finally {
+            programmaticTextFieldSet = false;
+        }
+    }
+
+    /**
+     * Returns the JavaFX node that represents this container and can be added to the scene graph.
+     *
+     * @return {@code this} container; never {@code null}
+     */
+    public Node asNode() {
+        return this;
+    }
+
+    /**
+     * Applies visibility to the ComboBox and TextField based on whether the list is active.
+     *
+     * @param listActive {@code true} to show the ComboBox, {@code false} to show the TextField
+     */
+    private void applyVisibility(boolean listActive) {
+        comboBox.setVisible(listActive);
+        comboBox.setManaged(listActive);
+        textField.setVisible(!listActive);
+        textField.setManaged(!listActive);
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiModelSource.java b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiModelSource.java
new file mode 100644
index 0000000..617a5bd
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiModelSource.java
@@ -0,0 +1,54 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+/**
+ * Describes the origin of the currently displayed model value in the GUI model selection area.
+ * <p>
+ * The GUI uses this enum to decide which control to show for the model input:
+ * <ul>
+ *   <li>When the source is {@link #LIST_REMOTE_SUCCESS}, a non-editable {@code ComboBox}
+ *       is shown, pre-populated with the remote list.</li>
+ *   <li>When the source is {@link #LIST_UNAVAILABLE_MANUAL_INPUT} or
+ *       {@link #LIST_FAILED_MANUAL_INPUT}, a plain text input field is shown instead,
+ *       allowing the user to enter the model name manually.</li>
+ *   <li>{@link #NOT_YET_LOADED} represents the initial state before the first retrieval
+ *       attempt; the GUI should render a loading indicator or show the text field
+ *       in a disabled/pending state.</li>
+ * </ul>
+ * <p>
+ * This enum is intentionally free of JavaFX references so it can be used in unit-tested
+ * view-model code without starting a JavaFX runtime.
+ */
+public enum GuiModelSource {
+
+    /**
+     * The model list was successfully retrieved from the remote provider endpoint.
+     * <p>
+     * A non-editable {@code ComboBox} is displayed, pre-selecting the first available model.
+     */
+    LIST_REMOTE_SUCCESS,
+
+    /**
+     * No model list is available because the provider does not expose a model catalogue endpoint
+     * or because the configuration was incomplete.
+     * <p>
+     * A manual text input field is shown and the user must enter the model identifier by hand.
+     */
+    LIST_UNAVAILABLE_MANUAL_INPUT,
+
+    /**
+     * A technical error occurred while retrieving the model list (e.g., HTTP error, timeout,
+     * authentication failure).
+     * <p>
+     * A manual text input field is shown so the user can still supply a model name; the GUI
+     * also reports the failure in the central message area.
+     */
+    LIST_FAILED_MANUAL_INPUT,
+
+    /**
+     * The initial state before the first model retrieval attempt has been made.
+     * <p>
+     * The GUI should indicate that a retrieval is pending and must not present the manual
+     * input field as the definitive fallback until at least one retrieval attempt has completed.
+     */
+    NOT_YET_LOADED
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiVisibleProviderSection.java b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiVisibleProviderSection.java
new file mode 100644
index 0000000..2f030cb
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiVisibleProviderSection.java
@@ -0,0 +1,98 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import java.util.Objects;
+
+import de.gecheckt.pdf.umbenenner.application.config.provider.AiProviderFamily;
+
+/**
+ * Represents which provider section is currently visible in the GUI and preserves
+ * the editable configuration state of the section that is currently hidden.
+ * <p>
+ * The GUI shows exactly one provider section at a time. When the user switches the
+ * active provider, the previously visible section must not lose its field values.
+ * This record captures the current display context as an immutable snapshot so that
+ * view-model code can reason about visibility and data preservation without touching
+ * JavaFX nodes directly.
+ * <p>
+ * Instances of this record contain no JavaFX references and are safe to create and
+ * inspect from any thread, including unit-test threads.
+ *
+ * @param visibleProvider          the provider family whose configuration section is
+ *                                 currently rendered; never {@code null}
+ * @param visibleProviderState     the editable configuration state currently displayed;
+ *                                 never {@code null}
+ * @param hiddenProviderState      the editable configuration state of the provider that
+ *                                 is not shown, preserved here so it is not lost on switch;
+ *                                 never {@code null}
+ * @param hiddenProvider           the provider family whose section is currently hidden;
+ *                                 never {@code null}
+ */
+public record GuiVisibleProviderSection(
+        AiProviderFamily visibleProvider,
+        GuiProviderConfigurationState visibleProviderState,
+        AiProviderFamily hiddenProvider,
+        GuiProviderConfigurationState hiddenProviderState) {
+
+    /**
+     * Creates a new visible-provider section snapshot.
+     *
+     * @param visibleProvider      provider whose section is shown; must not be {@code null}
+     * @param visibleProviderState configuration state of the visible provider; must not be {@code null}
+     * @param hiddenProvider       provider whose section is hidden; must not be {@code null}
+     * @param hiddenProviderState  configuration state of the hidden provider; must not be {@code null}
+     * @throws NullPointerException     if any parameter is {@code null}
+     * @throws IllegalArgumentException if {@code visibleProvider} and {@code hiddenProvider} are equal
+     */
+    public GuiVisibleProviderSection {
+        Objects.requireNonNull(visibleProvider, "visibleProvider must not be null");
+        Objects.requireNonNull(visibleProviderState, "visibleProviderState must not be null");
+        Objects.requireNonNull(hiddenProvider, "hiddenProvider must not be null");
+        Objects.requireNonNull(hiddenProviderState, "hiddenProviderState must not be null");
+        if (visibleProvider == hiddenProvider) {
+            throw new IllegalArgumentException(
+                    "visibleProvider and hiddenProvider must be different, but both are: " + visibleProvider);
+        }
+    }
+
+    /**
+     * Returns the configuration state for the requested provider family.
+     *
+     * @param family the provider family to retrieve the state for; must not be {@code null}
+     * @return the state for the requested provider
+     * @throws IllegalArgumentException if the requested family is neither the visible nor the hidden provider
+     */
+    public GuiProviderConfigurationState stateFor(AiProviderFamily family) {
+        Objects.requireNonNull(family, "family must not be null");
+        if (family == visibleProvider) {
+            return visibleProviderState;
+        }
+        if (family == hiddenProvider) {
+            return hiddenProviderState;
+        }
+        throw new IllegalArgumentException("Unknown provider family: " + family);
+    }
+
+    /**
+     * Returns a copy with the visible and hidden providers swapped, preserving both states.
+     * <p>
+     * The previously hidden provider becomes visible and the previously visible provider
+     * moves to hidden. No field values are lost during the switch.
+     *
+     * @return a new section snapshot with providers and their states swapped
+     */
+    public GuiVisibleProviderSection switchProvider() {
+        return new GuiVisibleProviderSection(hiddenProvider, hiddenProviderState,
+                visibleProvider, visibleProviderState);
+    }
+
+    /**
+     * Returns a copy with a different configuration state for the visible provider.
+     *
+     * @param newState the updated configuration state; must not be {@code null}
+     * @return a new section snapshot with the visible provider's state replaced
+     */
+    public GuiVisibleProviderSection withVisibleProviderState(GuiProviderConfigurationState newState) {
+        Objects.requireNonNull(newState, "newState must not be null");
+        return new GuiVisibleProviderSection(visibleProvider, newState, hiddenProvider, hiddenProviderState);
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/package-info.java b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/package-info.java
index 00337bf..c32bc13 100644
--- a/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/package-info.java
+++ b/pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/package-info.java
@@ -1,12 +1,41 @@
 /**
- * Editor state and template model for the JavaFX configuration editor.
+ * Editor state and view-model types for the JavaFX configuration editor.
  * <p>
  * This package contains the GUI-side representation of configuration data that can be edited
- * independently from file I/O and validation. It separates loaded file snapshots, baseline
- * editor values, current editor values, provider-specific API key state, and the derived
- * dirty-state view used by the GUI.
+ * independently from file I/O and validation. It covers:
+ * <ul>
+ *   <li>Loaded file snapshots, baseline editor values, current editor values and the derived
+ *       dirty-state view ({@link de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationEditorState},
+ *       {@link de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationValues}).</li>
+ *   <li>Provider-specific configuration state and API-key state
+ *       ({@link de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiProviderConfigurationState},
+ *       {@link de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiProviderApiKeyState}).</li>
+ *   <li>Provider section visibility and state preservation across provider switches
+ *       ({@link de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiVisibleProviderSection}).</li>
+ *   <li>Model source classification, manual model entry, and the JavaFX model field container
+ *       that switches between a non-editable {@code ComboBox} and a text field depending on
+ *       retrieval outcome
+ *       ({@link de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiModelSource},
+ *       {@link de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiManualModelEntry},
+ *       {@link de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiModelFieldContainer}).</li>
+ *   <li>Message severity, central message entries and field-level validation findings
+ *       ({@link de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiMessageSeverity},
+ *       {@link de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiMessageEntry},
+ *       {@link de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiFieldFinding}).</li>
+ *   <li>The consolidated validation result that feeds both the central message area and
+ *       field-near error display
+ *       ({@link de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiEditorValidationResult}).</li>
+ * </ul>
  * <p>
- * The classes in this package are intentionally free of JavaFX controls so they can be reused
- * by later GUI layers without coupling the model to a particular layout implementation.
+ * Most classes in this package are intentionally free of JavaFX controls so they can be used
+ * in unit-tested view-model code without starting a JavaFX runtime. The exception is
+ * {@link de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiModelFieldContainer}, which
+ * extends a JavaFX {@code StackPane} and must be used only on the JavaFX Application Thread.
+ * <p>
+ * Types that are not GUI-specific (API-key origin provenance, model catalogue results and
+ * the corresponding port contract) live in
+ * {@link de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog} to keep the
+ * Application module free of GUI dependencies while allowing future non-GUI consumers
+ * to reuse these types without depending on this adapter module.
  */
 package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiAdapterSmokeTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiAdapterSmokeTest.java
index 4306f38..844c3cf 100644
--- a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiAdapterSmokeTest.java
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiAdapterSmokeTest.java
@@ -395,7 +395,9 @@ class GuiAdapterSmokeTest {
                         GuiConfigurationTemplateFactory.createStandardTemplate(),
                         Optional.empty(),
                         configFilePath -> GuiConfigurationTemplateFactory.createStandardTemplate(),
-                        testWriter);
+                        testWriter,
+                        req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(), "kein Port im Test"),
+                        (family, propertyValue) -> de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor.absent());
                 GuiConfigurationEditorWorkspace workspace = new GuiConfigurationEditorWorkspace(context);
                 workspaceRef.set(workspace);
 
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorFieldBindingTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorFieldBindingTest.java
index 7dd0d5d..0201997 100644
--- a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorFieldBindingTest.java
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorFieldBindingTest.java
@@ -322,7 +322,9 @@ class GuiEditorFieldBindingTest {
                         GuiConfigurationTemplateFactory.createStandardTemplate(),
                         Optional.empty(),
                         configFilePath -> GuiConfigurationTemplateFactory.createStandardTemplate(),
-                        capturingWriter);
+                        capturingWriter,
+                        req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(), "kein Port im Test"),
+                        (family, propertyValue) -> de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor.absent());
                 GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(context);
                 ws.requestNewConfiguration();
 
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorIntegrationTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorIntegrationTest.java
index a14f6a6..247ba55 100644
--- a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorIntegrationTest.java
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorIntegrationTest.java
@@ -115,7 +115,9 @@ class GuiEditorIntegrationTest {
 
         GuiConfigurationEditorState loadedState = fileLoader.load(configFile);
         GuiConfigurationFileWriter noOpWriter = (values, path) -> GuiConfigurationSaveResult.saved(path);
-        GuiStartupContext context = new GuiStartupContext(loadedState, Optional.empty(), fileLoader, noOpWriter);
+        GuiStartupContext context = new GuiStartupContext(loadedState, Optional.empty(), fileLoader, noOpWriter,
+                req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(), "kein Port im Test"),
+                (family, propertyValue) -> de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor.absent());
 
         AtomicReference<Throwable> error = new AtomicReference<>();
         CountDownLatch latch = new CountDownLatch(1);
@@ -237,7 +239,9 @@ class GuiEditorIntegrationTest {
                 blankState,
                 Optional.of(notice),
                 configFilePath -> GuiConfigurationEditorStateFactory.createBlankStartState(),
-                noOpWriter);
+                noOpWriter,
+                req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(), "kein Port im Test"),
+                (family, propertyValue) -> de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor.absent());
 
         AtomicReference<Throwable> error = new AtomicReference<>();
         CountDownLatch latch = new CountDownLatch(1);
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorRegressionSmokeTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorRegressionSmokeTest.java
index e9dac86..e2b03dc 100644
--- a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorRegressionSmokeTest.java
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorRegressionSmokeTest.java
@@ -186,7 +186,9 @@ class GuiEditorRegressionSmokeTest {
         GuiConfigurationFileLoader loader = buildSnapshotLoader();
         GuiConfigurationFileWriter noOpWriter = (values, path) -> GuiConfigurationSaveResult.saved(path);
         GuiConfigurationEditorState initialState = GuiConfigurationEditorStateFactory.createBlankStartState();
-        GuiStartupContext context = new GuiStartupContext(initialState, Optional.empty(), loader, noOpWriter);
+        GuiStartupContext context = new GuiStartupContext(initialState, Optional.empty(), loader, noOpWriter,
+                req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(), "kein Port im Test"),
+                (family, propertyValue) -> de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor.absent());
 
         AtomicReference<GuiConfigurationEditorWorkspace> wsRef = new AtomicReference<>();
         AtomicReference<Throwable> error = new AtomicReference<>();
@@ -297,7 +299,9 @@ class GuiEditorRegressionSmokeTest {
                 stateWithFile,
                 Optional.empty(),
                 configFilePath -> GuiConfigurationTemplateFactory.createStandardTemplate(),
-                capturingWriter);
+                capturingWriter,
+                req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(), "kein Port im Test"),
+                (family, propertyValue) -> de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor.absent());
 
         CountDownLatch setupLatch = new CountDownLatch(1);
         Platform.runLater(() -> {
@@ -393,7 +397,9 @@ class GuiEditorRegressionSmokeTest {
                 GuiConfigurationTemplateFactory.createStandardTemplate(),
                 Optional.empty(),
                 configFilePath -> GuiConfigurationTemplateFactory.createStandardTemplate(),
-                capturingWriter);
+                capturingWriter,
+                req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(), "kein Port im Test"),
+                (family, propertyValue) -> de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor.absent());
 
         CountDownLatch setupLatch = new CountDownLatch(1);
         Platform.runLater(() -> {
@@ -493,7 +499,9 @@ class GuiEditorRegressionSmokeTest {
                 GuiConfigurationTemplateFactory.createStandardTemplate(),
                 Optional.empty(),
                 configFilePath -> GuiConfigurationTemplateFactory.createStandardTemplate(),
-                capturingWriter);
+                capturingWriter,
+                req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(), "kein Port im Test"),
+                (family, propertyValue) -> de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor.absent());
 
         CountDownLatch setupLatch = new CountDownLatch(1);
         Platform.runLater(() -> {
@@ -564,7 +572,9 @@ class GuiEditorRegressionSmokeTest {
                 GuiConfigurationTemplateFactory.createStandardTemplate(),
                 Optional.empty(),
                 configFilePath -> GuiConfigurationTemplateFactory.createStandardTemplate(),
-                trackingWriter);
+                trackingWriter,
+                req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(), "kein Port im Test"),
+                (family, propertyValue) -> de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor.absent());
 
         CountDownLatch setupLatch = new CountDownLatch(1);
         Platform.runLater(() -> {
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorValidationSmokeTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorValidationSmokeTest.java
new file mode 100644
index 0000000..7aa0123
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiEditorValidationSmokeTest.java
@@ -0,0 +1,456 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.IOException;
+import java.io.StringReader;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Optional;
+import java.util.Properties;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.BooleanSupplier;
+
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationEditorState;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationEditorStateFactory;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.GuiConfigurationSaveResult;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationFileSnapshot;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiEditorValidationResult;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiMessageSeverity;
+import javafx.application.Platform;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+/**
+ * Monocle-based headless smoke tests for the automatic editor validation.
+ * <p>
+ * These tests verify that the workspace triggers validation automatically when the editor
+ * state changes (via {@code applyEditorState} and {@code updateValues}) and that the
+ * {@link GuiEditorValidationResult} returned by {@code lastValidationResult()} reflects the
+ * current editor state.
+ *
+ * <h2>Covered scenarios</h2>
+ * <ul>
+ *   <li>Opening an incomplete configuration (missing active provider) produces ERROR findings
+ *       in {@code lastValidationResult} after the file is loaded.</li>
+ *   <li>Opening an incomplete configuration populates {@code pendingFieldFindings} with a
+ *       finding for {@code ai.provider.active}.</li>
+ *   <li>After {@code requestNewConfiguration}: template values replace blank values, validation
+ *       re-runs, {@code ai.provider.active} error disappears (valid provider in template);
+ *       a WARNING for the high {@code max.text.characters} value (5000) is present.</li>
+ *   <li>Changing a field via direct state update + re-applying state updates the validation
+ *       result with new findings.</li>
+ * </ul>
+ *
+ * <h2>Threading</h2>
+ * <p>
+ * All workspace interactions run on the FX Application Thread via {@link Platform#runLater}.
+ * The {@code openConfigurationFile} method uses a background thread internally; tests that use
+ * it await file-load completion via a polling helper before verifying results.
+ * The Monocle headless configuration is activated by the Surefire JVM arguments.
+ */
+class GuiEditorValidationSmokeTest {
+
+    private static final long FX_TIMEOUT_SECONDS = 10;
+    private static final AtomicBoolean PLATFORM_STARTED = new AtomicBoolean(false);
+
+    @BeforeAll
+    static void setUpJavaFxPlatform() throws InterruptedException {
+        Platform.setImplicitExit(false);
+        CountDownLatch latch = new CountDownLatch(1);
+        try {
+            Platform.startup(() -> {
+                PLATFORM_STARTED.set(true);
+                latch.countDown();
+            });
+            assertTrue(latch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                    "JavaFX Platform must start within timeout");
+        } catch (IllegalStateException alreadyStarted) {
+            CountDownLatch verifyLatch = new CountDownLatch(1);
+            Platform.runLater(() -> {
+                PLATFORM_STARTED.set(true);
+                verifyLatch.countDown();
+            });
+            assertTrue(verifyLatch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                    "Existing JavaFX Platform must be reachable within timeout");
+        }
+    }
+
+    @AfterAll
+    static void tearDownJavaFxPlatform() {
+        // Shared platform – do not call Platform.exit().
+    }
+
+    // =========================================================================
+    // Scenario: opening an incomplete configuration produces ERROR findings
+    // =========================================================================
+
+    /**
+     * Smoke test: when a properties file with an unknown (or empty) active-provider value is
+     * opened via {@link GuiConfigurationEditorWorkspace#openConfigurationFile}, the workspace
+     * calls {@code applyEditorState} after loading and runs validation automatically.
+     * <p>
+     * The resulting {@code lastValidationResult} must contain at least one ERROR because the
+     * active-provider field is empty.
+     *
+     * @param tempDir JUnit-provided temporary directory
+     * @throws Exception if the FX thread task fails or times out
+     */
+    @Test
+    void openingIncompleteConfiguration_validationRunsAndProducesErrors(@TempDir Path tempDir)
+            throws Exception {
+        // Write a properties file with an empty active provider.
+        Path configFile = tempDir.resolve("incomplete.properties");
+        writePropertiesFile(configFile, "" /* empty active provider */);
+
+        GuiConfigurationFileLoader loader = buildSnapshotLoader();
+        GuiConfigurationEditorState blankState =
+                GuiConfigurationEditorStateFactory.createBlankStartState();
+        GuiStartupContext ctx = new GuiStartupContext(
+                blankState, Optional.empty(), loader,
+                (values, path) -> GuiConfigurationSaveResult.saved(path),
+                req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog
+                        .ModelCatalogResult.IncompleteConfiguration(
+                                req.providerIdentifier(), "kein Port im Test"),
+                (family, propertyValue) ->
+                        de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog
+                                .EffectiveApiKeyDescriptor.absent());
+
+        AtomicReference<GuiConfigurationEditorWorkspace> wsRef = new AtomicReference<>();
+        AtomicReference<Throwable> error = new AtomicReference<>();
+
+        // Create workspace and trigger file load on the FX thread.
+        CountDownLatch setupLatch = new CountDownLatch(1);
+        Platform.runLater(() -> {
+            try {
+                GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(ctx);
+                wsRef.set(ws);
+                ws.openConfigurationFile(configFile);
+            } catch (Throwable t) {
+                error.set(t);
+            } finally {
+                setupLatch.countDown();
+            }
+        });
+        assertTrue(setupLatch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                "Setup must complete within timeout");
+        rethrow(error);
+
+        // Wait for the background loader thread to apply the state.
+        waitFor(() -> {
+            AtomicBoolean ready = new AtomicBoolean(false);
+            CountDownLatch check = new CountDownLatch(1);
+            Platform.runLater(() -> {
+                GuiConfigurationEditorWorkspace ws = wsRef.get();
+                if (ws != null && ws.editorState().hasLoadedFileSnapshot()) {
+                    ready.set(true);
+                }
+                check.countDown();
+            });
+            try {
+                check.await(2, TimeUnit.SECONDS);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            }
+            return ready.get();
+        }, FX_TIMEOUT_SECONDS);
+
+        // Verify validation result on the FX thread.
+        CountDownLatch verifyLatch = new CountDownLatch(1);
+        Platform.runLater(() -> {
+            try {
+                GuiConfigurationEditorWorkspace ws = wsRef.get();
+                GuiEditorValidationResult result = ws.lastValidationResult();
+
+                assertNotNull(result, "lastValidationResult must never be null");
+                assertTrue(result.hasErrors(),
+                        "Loading a config with empty active provider must produce ERROR findings");
+                assertTrue(result.hasFieldFindingFor("ai.provider.active"),
+                        "pendingFieldFindings must contain a finding for 'ai.provider.active'"
+                        + " when the active provider is empty in the loaded file");
+            } catch (Throwable t) {
+                error.set(t);
+            } finally {
+                verifyLatch.countDown();
+            }
+        });
+
+        assertTrue(verifyLatch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                "Verify latch must complete within timeout");
+        rethrow(error);
+    }
+
+    // =========================================================================
+    // Scenario: changing a field updates the validation result
+    // =========================================================================
+
+    /**
+     * Smoke test: when the active provider is changed from a valid value to an empty string via
+     * a direct state update followed by {@code requestNewConfiguration} (which calls
+     * {@code applyEditorState} and triggers {@code runEditorValidation}), the
+     * {@code lastValidationResult} is updated with findings that reflect the new state.
+     * <p>
+     * More concretely, this test demonstrates the field-change→re-validation flow by:
+     * <ol>
+     *   <li>Starting with the standard template (valid provider → no provider error).</li>
+     *   <li>Loading a file that has an empty provider (produces a provider ERROR).</li>
+     *   <li>Verifying that {@code lastValidationResult} changed from "no error" to "error" as
+     *       the result of loading the file with invalid values.</li>
+     * </ol>
+     *
+     * @param tempDir JUnit-provided temporary directory
+     * @throws Exception if the FX thread task fails or times out
+     */
+    @Test
+    void changingField_revalidatesAndUpdatesLastValidationResult(@TempDir Path tempDir)
+            throws Exception {
+        Path invalidConfig = tempDir.resolve("invalid-provider.properties");
+        writePropertiesFile(invalidConfig, "" /* empty active provider */);
+
+        GuiConfigurationFileLoader loader = buildSnapshotLoader();
+        GuiConfigurationEditorState blankState =
+                GuiConfigurationEditorStateFactory.createBlankStartState();
+        GuiStartupContext ctx = new GuiStartupContext(
+                blankState, Optional.empty(), loader,
+                (values, path) -> GuiConfigurationSaveResult.saved(path),
+                req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog
+                        .ModelCatalogResult.IncompleteConfiguration(
+                                req.providerIdentifier(), "kein Port im Test"),
+                (family, propertyValue) ->
+                        de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog
+                                .EffectiveApiKeyDescriptor.absent());
+
+        AtomicReference<GuiConfigurationEditorWorkspace> wsRef = new AtomicReference<>();
+        AtomicReference<Throwable> error = new AtomicReference<>();
+
+        CountDownLatch setupLatch = new CountDownLatch(1);
+        Platform.runLater(() -> {
+            try {
+                GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(ctx);
+                wsRef.set(ws);
+                // Step 1: apply template – validation runs with valid values.
+                ws.requestNewConfiguration();
+            } catch (Throwable t) {
+                error.set(t);
+            } finally {
+                setupLatch.countDown();
+            }
+        });
+        assertTrue(setupLatch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS), "Setup timeout");
+        rethrow(error);
+
+        // Confirm valid state after template.
+        CountDownLatch checkValidLatch = new CountDownLatch(1);
+        Platform.runLater(() -> {
+            try {
+                GuiConfigurationEditorWorkspace ws = wsRef.get();
+                assertFalse(ws.lastValidationResult().hasFieldFindingFor("ai.provider.active"),
+                        "After 'Neu' with valid template the active-provider field must have no error");
+            } catch (Throwable t) {
+                error.set(t);
+            } finally {
+                checkValidLatch.countDown();
+            }
+        });
+        assertTrue(checkValidLatch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS), "Check timeout");
+        rethrow(error);
+
+        // Step 2: trigger field change by loading an invalid config file.
+        CountDownLatch loadLatch = new CountDownLatch(1);
+        Platform.runLater(() -> {
+            try {
+                wsRef.get().openConfigurationFile(invalidConfig);
+            } catch (Throwable t) {
+                error.set(t);
+            } finally {
+                loadLatch.countDown();
+            }
+        });
+        assertTrue(loadLatch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS), "Load trigger timeout");
+        rethrow(error);
+
+        // Wait for background loader.
+        waitFor(() -> {
+            AtomicBoolean ready = new AtomicBoolean(false);
+            CountDownLatch check = new CountDownLatch(1);
+            Platform.runLater(() -> {
+                GuiConfigurationEditorWorkspace ws = wsRef.get();
+                if (ws != null && ws.editorState().hasLoadedFileSnapshot()) {
+                    ready.set(true);
+                }
+                check.countDown();
+            });
+            try {
+                check.await(2, TimeUnit.SECONDS);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            }
+            return ready.get();
+        }, FX_TIMEOUT_SECONDS);
+
+        // Verify: invalid provider is now detected.
+        CountDownLatch verifyLatch = new CountDownLatch(1);
+        Platform.runLater(() -> {
+            try {
+                GuiConfigurationEditorWorkspace ws = wsRef.get();
+                GuiEditorValidationResult result = ws.lastValidationResult();
+                assertTrue(result.hasErrors(),
+                        "After loading a config with empty active provider, result must have errors");
+                assertTrue(result.hasFieldFindingFor("ai.provider.active"),
+                        "After loading invalid config, active-provider finding must be present");
+            } catch (Throwable t) {
+                error.set(t);
+            } finally {
+                verifyLatch.countDown();
+            }
+        });
+        assertTrue(verifyLatch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS), "Verify timeout");
+        rethrow(error);
+    }
+
+    // =========================================================================
+    // Scenario: standard template validation – WARNING for max.text.characters
+    // =========================================================================
+
+    /**
+     * Smoke test: after {@code requestNewConfiguration}, the standard template values are active
+     * and validation runs. The template sets {@code max.text.characters = 5000} which exceeds the
+     * 3 000 strong-warning threshold → at least one WARNING is expected. The template also sets
+     * a valid active provider → no ERROR for that field.
+     *
+     * @throws Exception if the FX thread task fails or times out
+     */
+    @Test
+    void requestNewConfiguration_triggersValidation_templateProducesWarningForHighCharLimit()
+            throws Exception {
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws =
+                    new GuiConfigurationEditorWorkspace(Optional.empty());
+            ws.requestNewConfiguration();
+
+            GuiEditorValidationResult result = ws.lastValidationResult();
+            assertNotNull(result, "lastValidationResult must not be null after 'Neu'");
+
+            // Template has valid provider → no field finding for ai.provider.active.
+            assertFalse(result.hasFieldFindingFor("ai.provider.active"),
+                    "Standard template has a valid provider; 'ai.provider.active' must have"
+                    + " no field finding");
+
+            // Template max.text.characters = 5000 (>3000) → at least one WARNING.
+            boolean hasWarningOrAbove = result.messages().stream()
+                    .anyMatch(m -> m.severity() == GuiMessageSeverity.WARNING
+                            || m.severity() == GuiMessageSeverity.ERROR);
+            assertTrue(hasWarningOrAbove,
+                    "Standard template with max.text.characters=5000 must produce at least"
+                    + " one WARNING in the validation messages");
+        });
+    }
+
+    // =========================================================================
+    // Scenario: pendingFieldFindings updated by applyEditorState
+    // =========================================================================
+
+    /**
+     * Smoke test: after {@code requestNewConfiguration}, the {@code pendingFieldFindings} list is
+     * updated and the template's valid provider is not flagged.
+     *
+     * @throws Exception if the FX thread task fails or times out
+     */
+    @Test
+    void requestNewConfiguration_pendingFieldFindings_noProviderError() throws Exception {
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws =
+                    new GuiConfigurationEditorWorkspace(Optional.empty());
+            ws.requestNewConfiguration();
+
+            assertNotNull(ws.pendingFieldFindings, "pendingFieldFindings must never be null");
+            assertFalse(ws.pendingFieldFindings.stream()
+                    .anyMatch(f -> "ai.provider.active".equals(f.fieldKey())),
+                    "Standard template has a valid provider; no field finding expected for"
+                    + " 'ai.provider.active'");
+        });
+    }
+
+    // =========================================================================
+    // Helpers
+    // =========================================================================
+
+    private static GuiConfigurationFileLoader buildSnapshotLoader() {
+        return path -> {
+            try {
+                String content = Files.readString(path, StandardCharsets.UTF_8);
+                Properties props = new Properties();
+                props.load(new StringReader(content));
+                GuiConfigurationFileSnapshot snapshot = new GuiConfigurationFileSnapshot(path, props);
+                return GuiConfigurationEditorStateFactory.fromPropertiesSnapshot(
+                        snapshot, Optional.empty());
+            } catch (IOException e) {
+                throw new GuiConfigurationLoadException("Failed to load " + path, e);
+            }
+        };
+    }
+
+    private static void writePropertiesFile(Path path, String activeProvider) throws IOException {
+        String content = "source.folder=./work/source\n"
+                + "target.folder=./work/target\n"
+                + "ai.provider.active=" + activeProvider + "\n"
+                + "sqlite.file=./work/test.db\n"
+                + "max.retries.transient=3\n"
+                + "max.pages=10\n"
+                + "max.text.characters=500\n"
+                + "prompt.template.file=./config/prompt.txt\n";
+        Files.writeString(path, content, StandardCharsets.UTF_8);
+    }
+
+    private static void runOnFx(ThrowingRunnable task) throws Exception {
+        AtomicReference<Throwable> error = new AtomicReference<>();
+        CountDownLatch latch = new CountDownLatch(1);
+        Platform.runLater(() -> {
+            try {
+                task.run();
+            } catch (Throwable t) {
+                error.set(t);
+            } finally {
+                latch.countDown();
+            }
+        });
+        assertTrue(latch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                "FX task must complete within timeout");
+        rethrow(error);
+    }
+
+    private static void rethrow(AtomicReference<Throwable> error) throws Exception {
+        Throwable t = error.get();
+        if (t == null) {
+            return;
+        }
+        if (t instanceof Exception ex) {
+            throw ex;
+        }
+        throw new AssertionError("Unexpected error", t);
+    }
+
+    private static void waitFor(BooleanSupplier condition, long timeoutSeconds)
+            throws InterruptedException {
+        long deadline = System.currentTimeMillis() + timeoutSeconds * 1000L;
+        while (!condition.getAsBoolean()) {
+            assertTrue(System.currentTimeMillis() < deadline,
+                    "Condition was not met within the timeout");
+            Thread.sleep(50);
+        }
+    }
+
+    @FunctionalInterface
+    private interface ThrowingRunnable {
+        void run() throws Exception;
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiMessageAreaSmokeTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiMessageAreaSmokeTest.java
new file mode 100644
index 0000000..2d6e022
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiMessageAreaSmokeTest.java
@@ -0,0 +1,710 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.IOException;
+import java.io.StringReader;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Optional;
+import java.util.Properties;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.BooleanSupplier;
+
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationEditorStateFactory;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationFileSnapshot;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiMessageSeverity;
+import de.gecheckt.pdf.umbenenner.application.config.provider.AiProviderFamily;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult;
+import javafx.application.Platform;
+import javafx.scene.control.Label;
+import javafx.scene.text.Text;
+import javafx.scene.text.TextFlow;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+/**
+ * Monocle-based headless smoke tests for the central message area, field-level error labels
+ * and API-key origin display introduced in the message-area integration step.
+ *
+ * <h2>Covered scenarios</h2>
+ * <ul>
+ *   <li>After opening an incomplete configuration, ERROR entries are visible in the central
+ *       message area (non-zero child count in {@code messagesAreaBox}).</li>
+ *   <li>The first child of an ERROR row is a coloured {@link Text} prefix node; the second
+ *       child (body) carries black fill.</li>
+ *   <li>After opening a configuration with a missing source folder, the field-level error label
+ *       registered for {@code source.folder} is visible.</li>
+ *   <li>After the standard template is applied via {@code requestNewConfiguration()}, the
+ *       {@code source.folder} error label is hidden.</li>
+ *   <li>The WARNING threshold for {@code max.text.characters} (1001–3000) appears in the
+ *       central message area with a WARNING-coloured prefix.</li>
+ *   <li>After synchronous model-catalogue retrieval, the central message area is updated via the
+ *       post-result callback.</li>
+ *   <li>When the API-key resolution port reports an ENV-variable origin for Claude, the
+ *       api-key origin label is visible and references the variable name.</li>
+ *   <li>The field-error label for {@code ai.provider.active} is registered and shown when the
+ *       active provider is empty.</li>
+ * </ul>
+ *
+ * <h2>Threading</h2>
+ * All workspace interactions run on the JavaFX Application Thread via {@link Platform#runLater}.
+ * Model-catalogue retrieval is made synchronous via the coordinator's injectable factories so no
+ * real background threads are used and results are delivered inline.
+ */
+class GuiMessageAreaSmokeTest {
+
+    private static final long FX_TIMEOUT_SECONDS = 10;
+    private static final AtomicBoolean PLATFORM_STARTED = new AtomicBoolean(false);
+
+    @BeforeAll
+    static void setUpJavaFxPlatform() throws InterruptedException {
+        Platform.setImplicitExit(false);
+        CountDownLatch latch = new CountDownLatch(1);
+        try {
+            Platform.startup(() -> {
+                PLATFORM_STARTED.set(true);
+                latch.countDown();
+            });
+            assertTrue(latch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                    "JavaFX Platform must start within timeout");
+        } catch (IllegalStateException alreadyStarted) {
+            CountDownLatch verifyLatch = new CountDownLatch(1);
+            Platform.runLater(() -> {
+                PLATFORM_STARTED.set(true);
+                verifyLatch.countDown();
+            });
+            assertTrue(verifyLatch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                    "Existing JavaFX Platform must be reachable within timeout");
+        }
+    }
+
+    @AfterAll
+    static void tearDownJavaFxPlatform() {
+        // Shared platform — do not call Platform.exit().
+    }
+
+    // =========================================================================
+    // Scenario: central message area has ERROR entries for incomplete config
+    // =========================================================================
+
+    /**
+     * Smoke test: after opening a properties file with an empty active-provider value, the
+     * central {@code messagesAreaBox} contains at least one row, and at least one row has an
+     * ERROR-coloured prefix node.
+     */
+    @Test
+    void incompleteConfig_messagesAreaContainsErrorRow(@TempDir Path tempDir) throws Exception {
+        Path configFile = tempDir.resolve("incomplete.properties");
+        writePropertiesFile(configFile, "" /* empty active provider */, "500");
+
+        AtomicReference<GuiConfigurationEditorWorkspace> wsRef = new AtomicReference<>();
+        openConfigAndWait(configFile, wsRef);
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = wsRef.get();
+            assertFalse(ws.messagesAreaBox.getChildren().isEmpty(),
+                    "Central message area must not be empty after loading an incomplete configuration");
+
+            boolean foundErrorRow = ws.messagesAreaBox.getChildren().stream()
+                    .filter(n -> n instanceof TextFlow)
+                    .map(n -> (TextFlow) n)
+                    .anyMatch(tf -> {
+                        if (tf.getChildren().isEmpty()) {
+                            return false;
+                        }
+                        Object first = tf.getChildren().get(0);
+                        if (first instanceof Text t) {
+                            return t.getStyle().contains(GuiMessageSeverity.ERROR.getPrefixCssColour());
+                        }
+                        return false;
+                    });
+            assertTrue(foundErrorRow,
+                    "At least one TextFlow row must have an ERROR-coloured prefix node");
+        });
+    }
+
+    /**
+     * Smoke test: the body-text node of any message row must carry the black fill style.
+     */
+    @Test
+    void messageRow_bodyTextIsBlack(@TempDir Path tempDir) throws Exception {
+        Path configFile = tempDir.resolve("incomplete2.properties");
+        writePropertiesFile(configFile, "" /* empty active provider */, "500");
+
+        AtomicReference<GuiConfigurationEditorWorkspace> wsRef = new AtomicReference<>();
+        openConfigAndWait(configFile, wsRef);
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = wsRef.get();
+            Optional<TextFlow> anyRow = ws.messagesAreaBox.getChildren().stream()
+                    .filter(n -> n instanceof TextFlow)
+                    .map(n -> (TextFlow) n)
+                    .filter(tf -> tf.getChildren().size() >= 2)
+                    .findFirst();
+            assertTrue(anyRow.isPresent(), "Expected at least one TextFlow with two children");
+            Object bodyNode = anyRow.get().getChildren().get(1);
+            assertTrue(bodyNode instanceof Text, "Second child of a message row must be a Text node");
+            String bodyStyle = ((Text) bodyNode).getStyle();
+            // Body must be explicitly styled black or have no colour override at all.
+            assertTrue(bodyStyle.contains("black") || bodyStyle.contains("#000000")
+                            || bodyStyle.contains("000"),
+                    "Body text must be rendered in black; style: " + bodyStyle);
+        });
+    }
+
+    // =========================================================================
+    // Scenario: field-level error label for source.folder
+    // =========================================================================
+
+    /**
+     * Smoke test: when a configuration with a blank source folder is opened, the field-error label
+     * for {@code source.folder} is visible and non-blank.
+     */
+    @Test
+    void blankSourceFolder_fieldErrorLabelVisible(@TempDir Path tempDir) throws Exception {
+        Path configFile = tempDir.resolve("nosrc.properties");
+        writePropertiesFileBlankSourceFolder(configFile);
+
+        AtomicReference<GuiConfigurationEditorWorkspace> wsRef = new AtomicReference<>();
+        openConfigAndWait(configFile, wsRef);
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = wsRef.get();
+            Label errorLabel = ws.fieldErrorLabels.get("source.folder");
+            assertNotNull(errorLabel,
+                    "A field-error label must be registered for 'source.folder'");
+            assertTrue(errorLabel.isVisible(),
+                    "source.folder error label must be visible when the field is blank");
+            assertFalse(errorLabel.getText().isBlank(),
+                    "source.folder error label must carry a non-blank error text");
+        });
+    }
+
+    /**
+     * Smoke test: after applying the standard template via {@code requestNewConfiguration()}, the
+     * source.folder error label is hidden because the template supplies a non-blank value.
+     */
+    @Test
+    void standardTemplate_sourceFolderErrorLabelHidden() throws Exception {
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(Optional.empty());
+            ws.requestNewConfiguration();
+
+            Label errorLabel = ws.fieldErrorLabels.get("source.folder");
+            assertNotNull(errorLabel,
+                    "A field-error label must be registered for 'source.folder' after 'Neu'");
+            assertFalse(errorLabel.isVisible(),
+                    "source.folder error label must be hidden when the template provides a non-blank value");
+        });
+    }
+
+    // =========================================================================
+    // Scenario: WARNING for max.text.characters between 1001 and 3000
+    // =========================================================================
+
+    /**
+     * Smoke test: loading a config with {@code max.text.characters = 1500} (between 1001 and 3000)
+     * must produce at least one WARNING entry in the central message area.
+     */
+    @Test
+    void maxTextCharacters_warningThreshold_warningInMessages(@TempDir Path tempDir)
+            throws Exception {
+        Path configFile = tempDir.resolve("warning-chars.properties");
+        writePropertiesFile(configFile, "claude", "1500");
+
+        AtomicReference<GuiConfigurationEditorWorkspace> wsRef = new AtomicReference<>();
+        openConfigAndWait(configFile, wsRef);
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = wsRef.get();
+            boolean hasWarning = ws.messagesAreaBox.getChildren().stream()
+                    .filter(n -> n instanceof TextFlow)
+                    .map(n -> (TextFlow) n)
+                    .anyMatch(tf -> {
+                        if (tf.getChildren().isEmpty()) {
+                            return false;
+                        }
+                        Object first = tf.getChildren().get(0);
+                        if (first instanceof Text t) {
+                            return t.getStyle().contains(GuiMessageSeverity.WARNING.getPrefixCssColour());
+                        }
+                        return false;
+                    });
+            assertTrue(hasWarning,
+                    "max.text.characters=1500 must produce at least one WARNING row in the message area");
+        });
+    }
+
+    // =========================================================================
+    // Scenario: model-catalogue result updates the message area via postResultCallback
+    // =========================================================================
+
+    /**
+     * Smoke test: after a synchronous (inline) model-catalogue retrieval that returns an
+     * {@link ModelCatalogResult.IncompleteConfiguration} result, the central message area is
+     * updated and contains the coordinator's message with source "Modellabruf".
+     * <p>
+     * Both the thread factory and the result-delivery mechanism are replaced with synchronous
+     * implementations so the entire retrieval+delivery cycle completes within the FX thread call.
+     */
+    @Test
+    void modelCatalogResult_updatesMessageArea() throws Exception {
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(Optional.empty());
+            ws.requestNewConfiguration();
+
+            // Make retrieval fully synchronous: run the task inline and deliver result inline.
+            ws.modelCatalogCoordinator.modelCatalogThreadFactory = task -> new Thread(() -> task.run()) {
+                @Override
+                public void start() {
+                    // Execute the task inline on the calling thread instead of starting a new thread.
+                    this.run();
+                }
+            };
+            ws.modelCatalogCoordinator.resultDelivery = Runnable::run;
+
+            // Trigger retrieval for Claude — stub port returns IncompleteConfiguration.
+            ws.modelCatalogCoordinator.triggerModelRetrieval(
+                    AiProviderFamily.CLAUDE,
+                    de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiProviderConfigurationState.blank());
+
+            // The post-result callback must have called refreshMessagesArea().
+            assertFalse(ws.messagesAreaBox.getChildren().isEmpty(),
+                    "messagesAreaBox must not be empty after model-catalogue result was applied");
+
+            boolean hasModelCatalogEntry = ws.pendingMessages.stream()
+                    .anyMatch(m -> m.source().isPresent()
+                            && "Modellabruf".equals(m.source().get()));
+            assertTrue(hasModelCatalogEntry,
+                    "pendingMessages must contain at least one entry from source 'Modellabruf'"
+                    + " after retrieval");
+        });
+    }
+
+    // =========================================================================
+    // Scenario: API-key ENV-variable origin label
+    // =========================================================================
+
+    /**
+     * Smoke test: when the API-key resolution port reports that the Claude key comes from an
+     * environment variable, the api-key origin label below the Claude API-key field is visible
+     * and references the variable name or the concept of an environment variable.
+     */
+    @Test
+    void apiKeyFromEnvVariable_originLabelVisible() throws Exception {
+        GuiStartupContext ctx = new GuiStartupContext(
+                GuiConfigurationEditorStateFactory.createBlankStartState(),
+                Optional.empty(),
+                path -> { throw new GuiConfigurationLoadException("not used in test", null); },
+                (values, path) -> GuiConfigurationSaveResult.saved(path),
+                req -> new ModelCatalogResult.IncompleteConfiguration(
+                        req.providerIdentifier(), "kein Port im Test"),
+                (family, propertyValue) -> {
+                    if (family == AiProviderFamily.CLAUDE) {
+                        return EffectiveApiKeyDescriptor.fromProviderEnvVar("CLAUDE_API_KEY");
+                    }
+                    return EffectiveApiKeyDescriptor.absent();
+                });
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(ctx);
+            ws.requestNewConfiguration();
+
+            Label originLabel = ws.apiKeyOriginLabels.get(AiProviderFamily.CLAUDE);
+            assertNotNull(originLabel,
+                    "An api-key origin label must be registered for AiProviderFamily.CLAUDE");
+            assertTrue(originLabel.isVisible(),
+                    "Claude api-key origin label must be visible when key comes from ENV-variable");
+            String labelText = originLabel.getText();
+            assertTrue(labelText.contains("CLAUDE_API_KEY")
+                            || labelText.contains("Umgebungsvariable"),
+                    "Claude api-key origin label must reference the ENV-variable name or type;"
+                    + " got: " + labelText);
+        });
+    }
+
+    // =========================================================================
+    // Scenario: INFO-coloured prefix in the message area (model-catalogue success)
+    // =========================================================================
+
+    /**
+     * Smoke test: after a successful model-catalogue retrieval (stub returns Success), the central
+     * message area must contain at least one row whose prefix node carries the INFO colour.
+     * <p>
+     * This verifies that the INFO severity level is rendered with its defined CSS colour and not
+     * accidentally displayed with the ERROR or WARNING colour.
+     */
+    @Test
+    void successfulModelRetrieval_messagesAreaContainsInfoRow() throws Exception {
+        runOnFx(() -> {
+            GuiStartupContext ctx = new GuiStartupContext(
+                    GuiConfigurationEditorStateFactory.createBlankStartState(),
+                    Optional.empty(),
+                    path -> { throw new GuiConfigurationLoadException("not used in test", null); },
+                    (values, path) -> GuiConfigurationSaveResult.saved(path),
+                    req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog
+                            .ModelCatalogResult.Success(
+                                    req.providerIdentifier(),
+                                    java.util.List.of("claude-3-5-sonnet"),
+                                    java.time.Instant.now()),
+                    (family, propertyValue) -> EffectiveApiKeyDescriptor.absent());
+
+            GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(ctx);
+            // Make retrieval synchronous.
+            ws.modelCatalogCoordinator.modelCatalogThreadFactory = task -> new Thread(() -> task.run()) {
+                @Override
+                public void start() {
+                    this.run();
+                }
+            };
+            ws.modelCatalogCoordinator.resultDelivery = Runnable::run;
+
+            ws.requestNewConfiguration();
+
+            // Trigger retrieval so an INFO message is added.
+            ws.modelCatalogCoordinator.triggerModelRetrieval(
+                    AiProviderFamily.CLAUDE,
+                    de.gecheckt.pdf.umbenenner.adapter.in.gui.editor
+                            .GuiProviderConfigurationState.blank());
+
+            boolean foundInfoRow = ws.messagesAreaBox.getChildren().stream()
+                    .filter(n -> n instanceof TextFlow)
+                    .map(n -> (TextFlow) n)
+                    .anyMatch(tf -> {
+                        if (tf.getChildren().isEmpty()) {
+                            return false;
+                        }
+                        Object first = tf.getChildren().get(0);
+                        if (first instanceof Text t) {
+                            return t.getStyle().contains(GuiMessageSeverity.INFO.getPrefixCssColour());
+                        }
+                        return false;
+                    });
+            assertTrue(foundInfoRow,
+                    "After successful model retrieval at least one TextFlow row must have an"
+                    + " INFO-coloured prefix node");
+        });
+    }
+
+    // =========================================================================
+    // Scenario: HINT-coloured prefix in the message area (empty model list)
+    // =========================================================================
+
+    /**
+     * Smoke test: after a model-catalogue retrieval that returns {@code EmptyList}, the central
+     * message area must contain at least one row whose prefix node carries the HINT colour.
+     * <p>
+     * This verifies that the HINT severity level is correctly propagated from the coordinator to
+     * the rendered message area.
+     */
+    @Test
+    void emptyModelList_messagesAreaContainsHintRow() throws Exception {
+        runOnFx(() -> {
+            GuiStartupContext ctx = new GuiStartupContext(
+                    GuiConfigurationEditorStateFactory.createBlankStartState(),
+                    Optional.empty(),
+                    path -> { throw new GuiConfigurationLoadException("not used in test", null); },
+                    (values, path) -> GuiConfigurationSaveResult.saved(path),
+                    req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog
+                            .ModelCatalogResult.EmptyList(
+                                    req.providerIdentifier(), java.time.Instant.now()),
+                    (family, propertyValue) -> EffectiveApiKeyDescriptor.absent());
+
+            GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(ctx);
+            ws.modelCatalogCoordinator.modelCatalogThreadFactory = task -> new Thread(() -> task.run()) {
+                @Override
+                public void start() {
+                    this.run();
+                }
+            };
+            ws.modelCatalogCoordinator.resultDelivery = Runnable::run;
+
+            ws.requestNewConfiguration();
+
+            ws.modelCatalogCoordinator.triggerModelRetrieval(
+                    AiProviderFamily.CLAUDE,
+                    de.gecheckt.pdf.umbenenner.adapter.in.gui.editor
+                            .GuiProviderConfigurationState.blank());
+
+            boolean foundHintRow = ws.messagesAreaBox.getChildren().stream()
+                    .filter(n -> n instanceof TextFlow)
+                    .map(n -> (TextFlow) n)
+                    .anyMatch(tf -> {
+                        if (tf.getChildren().isEmpty()) {
+                            return false;
+                        }
+                        Object first = tf.getChildren().get(0);
+                        if (first instanceof Text t) {
+                            return t.getStyle().contains(GuiMessageSeverity.HINT.getPrefixCssColour());
+                        }
+                        return false;
+                    });
+            assertTrue(foundHintRow,
+                    "After EmptyList model retrieval at least one TextFlow row must have a"
+                    + " HINT-coloured prefix node");
+        });
+    }
+
+    // =========================================================================
+    // Scenario: strong WARNING for max.text.characters > 3000
+    // =========================================================================
+
+    /**
+     * Smoke test: loading a config with {@code max.text.characters = 3001} (above the 3000 strong
+     * warning threshold) must produce at least one WARNING entry in the central message area.
+     * <p>
+     * This verifies the upper threshold of the economic warning logic: values strictly above 3000
+     * trigger the strong warning level.
+     */
+    @Test
+    void maxTextCharacters_strongWarningThreshold_warningInMessages(@TempDir Path tempDir)
+            throws Exception {
+        Path configFile = tempDir.resolve("strong-warning-chars.properties");
+        writePropertiesFile(configFile, "claude", "3001");
+
+        AtomicReference<GuiConfigurationEditorWorkspace> wsRef = new AtomicReference<>();
+        openConfigAndWait(configFile, wsRef);
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = wsRef.get();
+            boolean hasWarning = ws.messagesAreaBox.getChildren().stream()
+                    .filter(n -> n instanceof TextFlow)
+                    .map(n -> (TextFlow) n)
+                    .anyMatch(tf -> {
+                        if (tf.getChildren().isEmpty()) {
+                            return false;
+                        }
+                        Object first = tf.getChildren().get(0);
+                        if (first instanceof Text t) {
+                            return t.getStyle().contains(GuiMessageSeverity.WARNING.getPrefixCssColour());
+                        }
+                        return false;
+                    });
+            assertTrue(hasWarning,
+                    "max.text.characters=3001 must produce at least one WARNING row in the"
+                    + " message area (strong-warning threshold)");
+        });
+    }
+
+    // =========================================================================
+    // Scenario: max.pages > 100 produces no ERROR field-finding (HINT only)
+    // =========================================================================
+
+    /**
+     * Smoke test: loading a config with {@code max.pages = 101} must not produce an ERROR
+     * field-finding for the {@code max.pages} key. High page counts are treated as
+     * plausibility/performance hints and must never block the configuration from being
+     * considered operational from the editor's perspective.
+     * <p>
+     * This complements the unit-level validation tests by verifying the finding is correctly
+     * mapped through the workspace pipeline and not accidentally escalated to ERROR.
+     */
+    @Test
+    void maxPages_over100_noErrorFieldFinding(@TempDir Path tempDir)
+            throws Exception {
+        Path configFile = tempDir.resolve("highpages.properties");
+        writePropertiesFileWithMaxPages(configFile, "claude", "500", "101");
+
+        AtomicReference<GuiConfigurationEditorWorkspace> wsRef = new AtomicReference<>();
+        openConfigAndWait(configFile, wsRef);
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = wsRef.get();
+            // The field-finding for max.pages must not be ERROR.
+            boolean hasErrorFindingForMaxPages = ws.pendingFieldFindings.stream()
+                    .anyMatch(f -> "max.pages".equals(f.fieldKey())
+                            && f.severity() == GuiMessageSeverity.ERROR);
+            assertFalse(hasErrorFindingForMaxPages,
+                    "max.pages=101 must not produce an ERROR field-finding; high page limits"
+                    + " are treated as plausibility hints only");
+        });
+    }
+
+    // =========================================================================
+    // Scenario: ai.provider.active field-error label is registered and shown
+    // =========================================================================
+
+    /**
+     * Smoke test: when the active provider is empty, the field-error label for
+     * {@code ai.provider.active} must be registered and visible.
+     */
+    @Test
+    void incompleteConfig_activeProviderFieldErrorLabelVisible(@TempDir Path tempDir)
+            throws Exception {
+        Path configFile = tempDir.resolve("noprovider.properties");
+        writePropertiesFile(configFile, "" /* empty */, "500");
+
+        AtomicReference<GuiConfigurationEditorWorkspace> wsRef = new AtomicReference<>();
+        openConfigAndWait(configFile, wsRef);
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = wsRef.get();
+            Label errorLabel = ws.fieldErrorLabels.get("ai.provider.active");
+            assertNotNull(errorLabel,
+                    "A field-error label must be registered for 'ai.provider.active'");
+            assertTrue(errorLabel.isVisible(),
+                    "'ai.provider.active' error label must be visible when provider is empty");
+        });
+    }
+
+    // =========================================================================
+    // Helpers
+    // =========================================================================
+
+    /**
+     * Opens {@code configFile} in a freshly created workspace and waits for the background loader
+     * to complete. The workspace reference is stored in {@code wsRef}.
+     */
+    private static void openConfigAndWait(Path configFile,
+                                          AtomicReference<GuiConfigurationEditorWorkspace> wsRef)
+            throws Exception {
+        GuiConfigurationFileLoader loader = buildSnapshotLoader();
+        GuiStartupContext ctx = new GuiStartupContext(
+                GuiConfigurationEditorStateFactory.createBlankStartState(),
+                Optional.empty(),
+                loader,
+                (values, path) -> GuiConfigurationSaveResult.saved(path),
+                req -> new ModelCatalogResult.IncompleteConfiguration(
+                        req.providerIdentifier(), "kein Port im Test"),
+                (family, propertyValue) -> EffectiveApiKeyDescriptor.absent());
+
+        CountDownLatch setupLatch = new CountDownLatch(1);
+        Platform.runLater(() -> {
+            try {
+                GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(ctx);
+                wsRef.set(ws);
+                ws.openConfigurationFile(configFile);
+            } finally {
+                setupLatch.countDown();
+            }
+        });
+        assertTrue(setupLatch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                "Setup must complete within timeout");
+
+        waitFor(() -> {
+            AtomicBoolean ready = new AtomicBoolean(false);
+            CountDownLatch check = new CountDownLatch(1);
+            Platform.runLater(() -> {
+                GuiConfigurationEditorWorkspace ws = wsRef.get();
+                if (ws != null && ws.editorState().hasLoadedFileSnapshot()) {
+                    ready.set(true);
+                }
+                check.countDown();
+            });
+            try {
+                check.await(2, TimeUnit.SECONDS);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            }
+            return ready.get();
+        }, FX_TIMEOUT_SECONDS);
+    }
+
+    private static GuiConfigurationFileLoader buildSnapshotLoader() {
+        return path -> {
+            try {
+                String content = Files.readString(path, StandardCharsets.UTF_8);
+                Properties props = new Properties();
+                props.load(new StringReader(content));
+                GuiConfigurationFileSnapshot snapshot = new GuiConfigurationFileSnapshot(path, props);
+                return GuiConfigurationEditorStateFactory.fromPropertiesSnapshot(
+                        snapshot, Optional.empty());
+            } catch (IOException e) {
+                throw new GuiConfigurationLoadException("Failed to load " + path, e);
+            }
+        };
+    }
+
+    private static void writePropertiesFile(Path path, String activeProvider,
+                                             String maxTextCharacters) throws IOException {
+        String content = "source.folder=./work/source\n"
+                + "target.folder=./work/target\n"
+                + "ai.provider.active=" + activeProvider + "\n"
+                + "sqlite.file=./work/test.db\n"
+                + "max.retries.transient=3\n"
+                + "max.pages=10\n"
+                + "max.text.characters=" + maxTextCharacters + "\n"
+                + "prompt.template.file=./config/prompt.txt\n";
+        Files.writeString(path, content, StandardCharsets.UTF_8);
+    }
+
+    private static void writePropertiesFileWithMaxPages(Path path, String activeProvider,
+                                                        String maxTextCharacters,
+                                                        String maxPages) throws IOException {
+        String content = "source.folder=./work/source\n"
+                + "target.folder=./work/target\n"
+                + "ai.provider.active=" + activeProvider + "\n"
+                + "sqlite.file=./work/test.db\n"
+                + "max.retries.transient=3\n"
+                + "max.pages=" + maxPages + "\n"
+                + "max.text.characters=" + maxTextCharacters + "\n"
+                + "prompt.template.file=./config/prompt.txt\n";
+        Files.writeString(path, content, StandardCharsets.UTF_8);
+    }
+
+    private static void writePropertiesFileBlankSourceFolder(Path path) throws IOException {
+        String content = "source.folder=\n"
+                + "target.folder=./work/target\n"
+                + "ai.provider.active=claude\n"
+                + "sqlite.file=./work/test.db\n"
+                + "max.retries.transient=3\n"
+                + "max.pages=10\n"
+                + "max.text.characters=500\n"
+                + "prompt.template.file=./config/prompt.txt\n";
+        Files.writeString(path, content, StandardCharsets.UTF_8);
+    }
+
+    private static void runOnFx(ThrowingRunnable task) throws Exception {
+        AtomicReference<Throwable> error = new AtomicReference<>();
+        CountDownLatch latch = new CountDownLatch(1);
+        Platform.runLater(() -> {
+            try {
+                task.run();
+            } catch (Throwable t) {
+                error.set(t);
+            } finally {
+                latch.countDown();
+            }
+        });
+        assertTrue(latch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                "FX task must complete within timeout");
+        rethrow(error);
+    }
+
+    private static void rethrow(AtomicReference<Throwable> error) throws Exception {
+        Throwable t = error.get();
+        if (t == null) {
+            return;
+        }
+        if (t instanceof Exception ex) {
+            throw ex;
+        }
+        throw new AssertionError("Unexpected error", t);
+    }
+
+    private static void waitFor(BooleanSupplier condition, long timeoutSeconds)
+            throws InterruptedException {
+        long deadline = System.currentTimeMillis() + timeoutSeconds * 1000L;
+        while (!condition.getAsBoolean()) {
+            assertTrue(System.currentTimeMillis() < deadline,
+                    "Condition was not met within the timeout");
+            Thread.sleep(50);
+        }
+    }
+
+    @FunctionalInterface
+    private interface ThrowingRunnable {
+        void run() throws Exception;
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiModelCatalogSmokeTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiModelCatalogSmokeTest.java
new file mode 100644
index 0000000..3796068
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiModelCatalogSmokeTest.java
@@ -0,0 +1,639 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.time.Instant;
+import java.util.List;
+import java.util.Optional;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
+
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiMessageEntry;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiMessageSeverity;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiModelFieldContainer;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiModelSource;
+import de.gecheckt.pdf.umbenenner.application.config.provider.AiProviderFamily;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.AiModelCatalogPort;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult;
+import javafx.application.Platform;
+import javafx.scene.Node;
+import javafx.scene.control.Button;
+import javafx.scene.control.ComboBox;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.MethodOrderer;
+import org.junit.jupiter.api.Order;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestMethodOrder;
+
+/**
+ * Smoke tests for the automatic model catalogue retrieval, the "Modelle neu laden" button,
+ * and the ComboBox/TextField switching behaviour in the provider section of the editor workspace.
+ *
+ * <p>All tests run on the JavaFX Application Thread under Monocle headless. The model catalogue
+ * port is replaced with a synchronous stub so no real HTTP calls are made and the tests are
+ * fully deterministic.
+ *
+ * <p>The coordinator's thread factory and result-delivery mechanism are both replaced with
+ * synchronous implementations so retrieval and result application happen inline on the calling
+ * thread (the FX thread in these tests). This avoids any async boundary and makes assertions
+ * immediately consistent after each trigger call.
+ */
+@TestMethodOrder(MethodOrderer.OrderAnnotation.class)
+class GuiModelCatalogSmokeTest {
+
+    private static final long FX_TIMEOUT_SECONDS = 10;
+    private static final AtomicBoolean PLATFORM_STARTED = new AtomicBoolean(false);
+
+    // =========================================================================
+    // JavaFX Platform lifecycle
+    // =========================================================================
+
+    @BeforeAll
+    static void setUpJavaFxPlatform() throws InterruptedException {
+        Platform.setImplicitExit(false);
+        CountDownLatch latch = new CountDownLatch(1);
+        try {
+            Platform.startup(() -> {
+                PLATFORM_STARTED.set(true);
+                latch.countDown();
+            });
+            assertTrue(latch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                    "JavaFX Platform must start within timeout");
+        } catch (IllegalStateException alreadyStarted) {
+            CountDownLatch verifyLatch = new CountDownLatch(1);
+            Platform.runLater(() -> {
+                PLATFORM_STARTED.set(true);
+                verifyLatch.countDown();
+            });
+            assertTrue(verifyLatch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                    "Existing JavaFX Platform must be reachable within timeout");
+        }
+    }
+
+    @AfterAll
+    static void tearDownJavaFxPlatform() {
+        // Shared platform — do not call Platform.exit().
+    }
+
+    // =========================================================================
+    // Test: Success result → ComboBox shown, first model pre-selected
+    // =========================================================================
+
+    /**
+     * When the model catalogue port returns a {@link ModelCatalogResult.Success}, the provider
+     * block's model field must switch to a non-editable ComboBox pre-selecting the first model.
+     */
+    @Test
+    @Order(1)
+    void successResult_comboBoxIsShownWithFirstModelSelected() throws Exception {
+        List<String> models = List.of("claude-3-5-sonnet", "claude-3-haiku");
+        AiModelCatalogPort stub = req ->
+                new ModelCatalogResult.Success(req.providerIdentifier(), models, Instant.now());
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = createWorkspaceWithStub(stub);
+            ws.requestNewConfiguration();
+
+            triggerRetrieval(ws, AiProviderFamily.CLAUDE);
+
+            GuiModelFieldContainer container = ws.modelFieldContainers.get(AiProviderFamily.CLAUDE);
+            assertNotNull(container, "Claude model field container must be present");
+            assertEquals(GuiModelSource.LIST_REMOTE_SUCCESS, container.currentSource(),
+                    "Source must be LIST_REMOTE_SUCCESS after successful retrieval");
+            assertEquals("claude-3-5-sonnet", container.currentModelValue(),
+                    "First model must be pre-selected");
+        });
+    }
+
+    // =========================================================================
+    // Test: EmptyList result → TextField shown
+    // =========================================================================
+
+    /**
+     * When the model catalogue port returns {@link ModelCatalogResult.EmptyList}, the provider
+     * block's model field must show the manual text field.
+     */
+    @Test
+    @Order(2)
+    void emptyListResult_textFieldIsShown() throws Exception {
+        AiModelCatalogPort stub = req ->
+                new ModelCatalogResult.EmptyList(req.providerIdentifier(), Instant.now());
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = createWorkspaceWithStub(stub);
+            ws.requestNewConfiguration();
+
+            triggerRetrieval(ws, AiProviderFamily.CLAUDE);
+
+            GuiModelFieldContainer container = ws.modelFieldContainers.get(AiProviderFamily.CLAUDE);
+            assertNotNull(container, "Claude model field container must be present");
+            assertEquals(GuiModelSource.LIST_UNAVAILABLE_MANUAL_INPUT, container.currentSource(),
+                    "Source must be LIST_UNAVAILABLE_MANUAL_INPUT for EmptyList result");
+        });
+    }
+
+    // =========================================================================
+    // Test: IncompleteConfiguration result → TextField shown
+    // =========================================================================
+
+    /**
+     * When the model catalogue port returns {@link ModelCatalogResult.IncompleteConfiguration},
+     * the provider block's model field must show the manual text field.
+     */
+    @Test
+    @Order(3)
+    void incompleteConfigResult_textFieldIsShown() throws Exception {
+        AiModelCatalogPort stub = req ->
+                new ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(), "API-Key fehlt.");
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = createWorkspaceWithStub(stub);
+            ws.requestNewConfiguration();
+
+            triggerRetrieval(ws, AiProviderFamily.CLAUDE);
+
+            GuiModelFieldContainer container = ws.modelFieldContainers.get(AiProviderFamily.CLAUDE);
+            assertNotNull(container, "Claude model field container must be present");
+            assertEquals(GuiModelSource.LIST_UNAVAILABLE_MANUAL_INPUT, container.currentSource(),
+                    "Source must be LIST_UNAVAILABLE_MANUAL_INPUT for IncompleteConfiguration");
+        });
+    }
+
+    // =========================================================================
+    // Test: TechnicalFailure result → TextField shown with FAILED state
+    // =========================================================================
+
+    /**
+     * When the model catalogue port returns {@link ModelCatalogResult.TechnicalFailure},
+     * the provider block's model field must show the manual text field in the failed state.
+     */
+    @Test
+    @Order(4)
+    void technicalFailureResult_textFieldIsShownWithFailedState() throws Exception {
+        AiModelCatalogPort stub = req ->
+                new ModelCatalogResult.TechnicalFailure(req.providerIdentifier(), "HTTP_ERROR",
+                        "Status 503");
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = createWorkspaceWithStub(stub);
+            ws.requestNewConfiguration();
+
+            triggerRetrieval(ws, AiProviderFamily.CLAUDE);
+
+            GuiModelFieldContainer container = ws.modelFieldContainers.get(AiProviderFamily.CLAUDE);
+            assertNotNull(container, "Claude model field container must be present");
+            assertEquals(GuiModelSource.LIST_FAILED_MANUAL_INPUT, container.currentSource(),
+                    "Source must be LIST_FAILED_MANUAL_INPUT for TechnicalFailure");
+        });
+    }
+
+    // =========================================================================
+    // Test: Manual value discarded when not in new list
+    // =========================================================================
+
+    /**
+     * When a manual model name is present in the text field and a subsequent successful
+     * retrieval returns a list that does NOT contain that name, the value must be discarded
+     * and the first item in the new list must be selected.
+     */
+    @Test
+    @Order(5)
+    void successResult_manualValueDiscardedWhenNotInList() throws Exception {
+        List<String> models = List.of("claude-3-5-sonnet", "claude-3-haiku");
+        AiModelCatalogPort stub = req ->
+                new ModelCatalogResult.Success(req.providerIdentifier(), models, Instant.now());
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = createWorkspaceWithStub(stub);
+            ws.requestNewConfiguration();
+
+            // Pre-set a manual value not present in the incoming list.
+            GuiModelFieldContainer container = ws.modelFieldContainers.get(AiProviderFamily.CLAUDE);
+            assertNotNull(container);
+            container.setTextFieldValue("my-custom-model");
+
+            triggerRetrieval(ws, AiProviderFamily.CLAUDE);
+
+            assertEquals(GuiModelSource.LIST_REMOTE_SUCCESS, container.currentSource(),
+                    "Source must be LIST_REMOTE_SUCCESS after successful retrieval");
+            assertEquals("claude-3-5-sonnet", container.currentModelValue(),
+                    "Manual value not in list must be discarded; first list item selected");
+        });
+    }
+
+    // =========================================================================
+    // Test: Manual value preserved when present in new list
+    // =========================================================================
+
+    /**
+     * When a manual model name is present in the text field and a subsequent successful
+     * retrieval returns a list that DOES contain that name, the selection must be preserved.
+     */
+    @Test
+    @Order(6)
+    void successResult_manualValuePreservedWhenInList() throws Exception {
+        List<String> models = List.of("claude-3-5-sonnet", "claude-3-haiku");
+        AiModelCatalogPort stub = req ->
+                new ModelCatalogResult.Success(req.providerIdentifier(), models, Instant.now());
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = createWorkspaceWithStub(stub);
+            ws.requestNewConfiguration();
+
+            GuiModelFieldContainer container = ws.modelFieldContainers.get(AiProviderFamily.CLAUDE);
+            assertNotNull(container);
+            // Pre-set a value that IS in the incoming list.
+            container.setTextFieldValue("claude-3-haiku");
+
+            triggerRetrieval(ws, AiProviderFamily.CLAUDE);
+
+            assertEquals(GuiModelSource.LIST_REMOTE_SUCCESS, container.currentSource(),
+                    "Source must be LIST_REMOTE_SUCCESS");
+            assertEquals("claude-3-haiku", container.currentModelValue(),
+                    "Manual value present in list must be preserved as selection");
+        });
+    }
+
+    // =========================================================================
+    // Test: Provider switch triggers automatic model retrieval
+    // =========================================================================
+
+    /**
+     * Switching the provider ComboBox must automatically trigger a model retrieval for the
+     * newly selected provider without requiring the user to press "Modelle neu laden".
+     */
+    @Test
+    @Order(7)
+    void providerSwitch_triggersAutomaticModelRetrieval() throws Exception {
+        List<String> openAiModels = List.of("gpt-4o", "gpt-4-turbo");
+        AiModelCatalogPort stub = req -> {
+            if (AiProviderFamily.OPENAI_COMPATIBLE.getIdentifier().equals(req.providerIdentifier())) {
+                return new ModelCatalogResult.Success(req.providerIdentifier(), openAiModels,
+                        Instant.now());
+            }
+            return new ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(),
+                    "Test-Stub: kein Claude-Abruf in diesem Test.");
+        };
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = createWorkspaceWithStub(stub);
+            ws.requestNewConfiguration();
+
+            // Switch the provider ComboBox from Claude to OpenAI; the listener auto-triggers retrieval.
+            ComboBox<AiProviderFamily> comboBox = findProviderComboBox(ws);
+            assertNotNull(comboBox, "Provider ComboBox must be present");
+            comboBox.setValue(AiProviderFamily.OPENAI_COMPATIBLE);
+            // Because resultDelivery is synchronous, retrieval and result application happened inline.
+
+            GuiModelFieldContainer openAiContainer =
+                    ws.modelFieldContainers.get(AiProviderFamily.OPENAI_COMPATIBLE);
+            assertNotNull(openAiContainer, "OpenAI model field container must be present");
+            assertEquals(GuiModelSource.LIST_REMOTE_SUCCESS, openAiContainer.currentSource(),
+                    "OpenAI model source must be LIST_REMOTE_SUCCESS after automatic retrieval on switch");
+            assertEquals("gpt-4o", openAiContainer.currentModelValue(),
+                    "First OpenAI model must be pre-selected after automatic retrieval");
+        });
+    }
+
+    // =========================================================================
+    // Test: "Modelle neu laden" button triggers retrieval
+    // =========================================================================
+
+    /**
+     * Pressing the "Modelle neu laden" button must trigger the same retrieval path as the
+     * automatic trigger on provider switch.
+     */
+    @Test
+    @Order(8)
+    void reloadModelsButton_triggersModelRetrieval() throws Exception {
+        List<String> models = List.of("claude-opus-4");
+        AiModelCatalogPort stub = req ->
+                new ModelCatalogResult.Success(req.providerIdentifier(), models, Instant.now());
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = createWorkspaceWithStub(stub);
+            ws.requestNewConfiguration();
+
+            Button reloadButton = findNodeById(ws, "modelle-neu-laden-button", Button.class);
+            assertNotNull(reloadButton, "\"Modelle neu laden\" button must be present in the scene graph");
+
+            reloadButton.fire();
+            // Because resultDelivery is synchronous, result is applied immediately.
+
+            GuiModelFieldContainer container = ws.modelFieldContainers.get(AiProviderFamily.CLAUDE);
+            assertNotNull(container, "Claude model field container must be present");
+            assertEquals(GuiModelSource.LIST_REMOTE_SUCCESS, container.currentSource(),
+                    "Source must be LIST_REMOTE_SUCCESS after pressing \"Modelle neu laden\"");
+            assertEquals("claude-opus-4", container.currentModelValue(),
+                    "Model returned by stub must be selected after reload");
+        });
+    }
+
+    // =========================================================================
+    // Test: pendingMessages list receives entry after each retrieval
+    // =========================================================================
+
+    /**
+     * After each model catalogue retrieval a {@link GuiMessageEntry} must be appended to
+     * {@link GuiConfigurationEditorWorkspace#pendingMessages}, regardless of the result type.
+     */
+    @Test
+    @Order(9)
+    void pendingMessages_entryAppendedAfterEachRetrieval() throws Exception {
+        AiModelCatalogPort stub = req ->
+                new ModelCatalogResult.TechnicalFailure(req.providerIdentifier(), "TIMEOUT",
+                        "Zeitüberschreitung");
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = createWorkspaceWithStub(stub);
+            ws.requestNewConfiguration();
+
+            int before = ws.pendingMessages.size();
+            triggerRetrieval(ws, AiProviderFamily.CLAUDE);
+
+            assertEquals(before + 1, ws.pendingMessages.size(),
+                    "Exactly one message entry must be appended after retrieval");
+            GuiMessageEntry entry = ws.pendingMessages.get(ws.pendingMessages.size() - 1);
+            assertEquals(GuiMessageSeverity.ERROR, entry.severity(),
+                    "TechnicalFailure must produce an ERROR message entry");
+            assertTrue(entry.source().isPresent(), "Message must have a source label");
+            assertEquals("Modellabruf", entry.source().get(),
+                    "Message source must be \"Modellabruf\"");
+        });
+    }
+
+    // =========================================================================
+    // Test: Success pendingMessage has INFO severity
+    // =========================================================================
+
+    /**
+     * A successful model list retrieval must append a message entry with {@link GuiMessageSeverity#INFO}.
+     */
+    @Test
+    @Order(10)
+    void pendingMessages_successProducesInfoEntry() throws Exception {
+        List<String> models = List.of("claude-3-5-sonnet");
+        AiModelCatalogPort stub = req ->
+                new ModelCatalogResult.Success(req.providerIdentifier(), models, Instant.now());
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = createWorkspaceWithStub(stub);
+            ws.requestNewConfiguration();
+
+            triggerRetrieval(ws, AiProviderFamily.CLAUDE);
+
+            assertFalse(ws.pendingMessages.isEmpty(), "pendingMessages must not be empty");
+            GuiMessageEntry last = ws.pendingMessages.get(ws.pendingMessages.size() - 1);
+            assertEquals(GuiMessageSeverity.INFO, last.severity(),
+                    "Successful retrieval must produce an INFO message");
+        });
+    }
+
+    // =========================================================================
+    // Test: IncompleteConfiguration pendingMessage has WARNING severity
+    // =========================================================================
+
+    /**
+     * An {@link ModelCatalogResult.IncompleteConfiguration} result must append a
+     * {@link GuiMessageSeverity#WARNING} entry.
+     */
+    @Test
+    @Order(11)
+    void pendingMessages_incompleteConfigProducesWarningEntry() throws Exception {
+        AiModelCatalogPort stub = req ->
+                new ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(),
+                        "Kein API-Key.");
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = createWorkspaceWithStub(stub);
+            ws.requestNewConfiguration();
+
+            triggerRetrieval(ws, AiProviderFamily.CLAUDE);
+
+            assertFalse(ws.pendingMessages.isEmpty(), "pendingMessages must not be empty");
+            GuiMessageEntry last = ws.pendingMessages.get(ws.pendingMessages.size() - 1);
+            assertEquals(GuiMessageSeverity.WARNING, last.severity(),
+                    "IncompleteConfiguration must produce a WARNING message");
+        });
+    }
+
+    // =========================================================================
+    // Test: EmptyList pendingMessage has HINT severity
+    // =========================================================================
+
+    /**
+     * An {@link ModelCatalogResult.EmptyList} result must append a
+     * {@link GuiMessageSeverity#HINT} entry.
+     */
+    @Test
+    @Order(12)
+    void pendingMessages_emptyListProducesHintEntry() throws Exception {
+        AiModelCatalogPort stub = req ->
+                new ModelCatalogResult.EmptyList(req.providerIdentifier(), Instant.now());
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = createWorkspaceWithStub(stub);
+            ws.requestNewConfiguration();
+
+            triggerRetrieval(ws, AiProviderFamily.CLAUDE);
+
+            assertFalse(ws.pendingMessages.isEmpty(), "pendingMessages must not be empty");
+            GuiMessageEntry last = ws.pendingMessages.get(ws.pendingMessages.size() - 1);
+            assertEquals(GuiMessageSeverity.HINT, last.severity(),
+                    "EmptyList must produce a HINT message");
+        });
+    }
+
+    // =========================================================================
+    // Test: repeated retrieval replaces previous message entry, not accumulates
+    // =========================================================================
+
+    /**
+     * Triggering model retrieval twice must not accumulate two "Modellabruf" entries in
+     * {@code pendingMessages}. The second trigger must replace the entry from the first trigger
+     * so that exactly one entry with source "Modellabruf" is present after both calls.
+     * <p>
+     * This verifies the fix that removes old "Modellabruf" entries at the start of
+     * {@code applyResult} before appending the new one.
+     */
+    @Test
+    @Order(13)
+    void pendingMessages_repeatedRetrieval_replacesNotAccumulates() throws Exception {
+        List<String> models = List.of("claude-3-5-sonnet");
+        AiModelCatalogPort stub = req ->
+                new ModelCatalogResult.Success(req.providerIdentifier(), models, Instant.now());
+
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = createWorkspaceWithStub(stub);
+            ws.requestNewConfiguration();
+
+            // Trigger retrieval twice for the same provider.
+            triggerRetrieval(ws, AiProviderFamily.CLAUDE);
+            triggerRetrieval(ws, AiProviderFamily.CLAUDE);
+
+            long modellabrufCount = ws.pendingMessages.stream()
+                    .filter(m -> m.source().isPresent()
+                            && "Modellabruf".equals(m.source().get()))
+                    .count();
+            assertEquals(1L, modellabrufCount,
+                    "After two retrieval triggers, exactly one 'Modellabruf' entry must remain in"
+                    + " pendingMessages (replace semantics, not accumulate)");
+        });
+    }
+
+    // =========================================================================
+    // Helpers: workspace creation with stub
+    // =========================================================================
+
+    /**
+     * Creates a workspace whose model catalogue coordinator is backed by the given stub port.
+     * Both the thread factory and result delivery are replaced with synchronous implementations
+     * so retrieval and result application happen inline without any async boundary.
+     *
+     * @param stub the stub port returning deterministic results; must not be {@code null}
+     * @return a workspace ready for testing; never {@code null}
+     */
+    private static GuiConfigurationEditorWorkspace createWorkspaceWithStub(AiModelCatalogPort stub) {
+        GuiStartupContext ctx = new GuiStartupContext(
+                de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationEditorStateFactory
+                        .createBlankStartState(),
+                Optional.empty(),
+                path -> de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationEditorStateFactory
+                        .createBlankStartState(),
+                (values, path) -> GuiConfigurationSaveResult.saved(path),
+                stub,
+                (family, propertyValue) -> de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor.absent());
+        GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(ctx);
+        // Synchronous thread factory: run the task directly instead of starting an OS thread.
+        ws.modelCatalogCoordinator.modelCatalogThreadFactory = task -> new Thread(task, "gui-model-catalog-test") {
+            @Override
+            public synchronized void start() {
+                run(); // run synchronously on the calling thread
+            }
+        };
+        // Synchronous result delivery: execute the callback directly instead of via Platform.runLater.
+        ws.modelCatalogCoordinator.resultDelivery = Runnable::run;
+        return ws;
+    }
+
+    /**
+     * Triggers model retrieval for the given family using the current editor state.
+     * Because the coordinator uses synchronous delivery, the result is applied immediately.
+     *
+     * @param ws     the workspace to trigger retrieval on; must not be {@code null}
+     * @param family the provider family to retrieve models for; must not be {@code null}
+     */
+    private static void triggerRetrieval(GuiConfigurationEditorWorkspace ws, AiProviderFamily family) {
+        de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiProviderConfigurationState pState =
+                Optional.ofNullable(ws.editorState().values().providerConfiguration(family))
+                        .orElse(de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiProviderConfigurationState
+                                .blank());
+        ws.modelCatalogCoordinator.triggerModelRetrieval(family, pState);
+    }
+
+    // =========================================================================
+    // Helpers: scene graph traversal
+    // =========================================================================
+
+    @SuppressWarnings("unchecked")
+    private static ComboBox<AiProviderFamily> findProviderComboBox(GuiConfigurationEditorWorkspace ws) {
+        return (ComboBox<AiProviderFamily>) findNodeDeep(ws.tabPane, ComboBox.class);
+    }
+
+    @SuppressWarnings("unchecked")
+    private static <T extends Node> T findNodeById(GuiConfigurationEditorWorkspace ws,
+                                                   String id, Class<T> type) {
+        return (T) findNodeByIdDeep(ws.tabPane, id);
+    }
+
+    private static Node findNodeByIdDeep(Node root, String id) {
+        if (id.equals(root.getId())) {
+            return root;
+        }
+        if (root instanceof javafx.scene.control.ScrollPane sp) {
+            Node content = sp.getContent();
+            if (content != null) {
+                Node found = findNodeByIdDeep(content, id);
+                if (found != null) return found;
+            }
+        } else if (root instanceof javafx.scene.control.TabPane tabPane) {
+            for (javafx.scene.control.Tab tab : tabPane.getTabs()) {
+                if (tab.getContent() != null) {
+                    Node found = findNodeByIdDeep(tab.getContent(), id);
+                    if (found != null) return found;
+                }
+            }
+        } else if (root instanceof javafx.scene.Parent parent) {
+            for (Node child : parent.getChildrenUnmodifiable()) {
+                Node found = findNodeByIdDeep(child, id);
+                if (found != null) return found;
+            }
+        }
+        return null;
+    }
+
+    private static Node findNodeDeep(Node root, Class<?> nodeType) {
+        if (nodeType.isInstance(root)) {
+            return root;
+        }
+        if (root instanceof javafx.scene.control.ScrollPane sp) {
+            Node content = sp.getContent();
+            if (content != null) {
+                Node found = findNodeDeep(content, nodeType);
+                if (found != null) return found;
+            }
+        } else if (root instanceof javafx.scene.control.TabPane tabPane) {
+            for (javafx.scene.control.Tab tab : tabPane.getTabs()) {
+                if (tab.getContent() != null) {
+                    Node found = findNodeDeep(tab.getContent(), nodeType);
+                    if (found != null) return found;
+                }
+            }
+        } else if (root instanceof javafx.scene.Parent parent) {
+            for (Node child : parent.getChildrenUnmodifiable()) {
+                Node found = findNodeDeep(child, nodeType);
+                if (found != null) return found;
+            }
+        }
+        return null;
+    }
+
+    // =========================================================================
+    // Threading helper
+    // =========================================================================
+
+    private static void runOnFx(ThrowingRunnable task) throws Exception {
+        CountDownLatch latch = new CountDownLatch(1);
+        AtomicReference<Throwable> error = new AtomicReference<>();
+        Platform.runLater(() -> {
+            try {
+                task.run();
+            } catch (Throwable t) {
+                error.set(t);
+            } finally {
+                latch.countDown();
+            }
+        });
+        assertTrue(latch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                "FX task must complete within timeout");
+        if (error.get() != null) {
+            Throwable t = error.get();
+            if (t instanceof Exception e) {
+                throw e;
+            }
+            throw new AssertionError("Unexpected error on FX thread", t);
+        }
+    }
+
+    @FunctionalInterface
+    private interface ThrowingRunnable {
+        void run() throws Exception;
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiProviderSelectionSmokeTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiProviderSelectionSmokeTest.java
new file mode 100644
index 0000000..ac8b3af
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiProviderSelectionSmokeTest.java
@@ -0,0 +1,452 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.Optional;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
+
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationTemplateFactory;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationValues;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiProviderConfigurationState;
+import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiVisibleProviderSection;
+import de.gecheckt.pdf.umbenenner.application.config.provider.AiProviderFamily;
+import javafx.application.Platform;
+import javafx.scene.control.ComboBox;
+import javafx.scene.Node;
+import javafx.scene.layout.VBox;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.MethodOrderer;
+import org.junit.jupiter.api.Order;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestMethodOrder;
+
+/**
+ * Smoke tests for the provider selection ComboBox, provider block visibility management
+ * and state preservation on provider switch.
+ *
+ * <p>All tests run on the JavaFX Application Thread under Monocle headless. The tests verify:
+ * <ul>
+ *   <li>Initial ComboBox selection matches the active provider from the editor state.</li>
+ *   <li>Only the active provider block is visible; the other is not visible and not managed.</li>
+ *   <li>After a provider switch the previously hidden provider's data is still intact in the
+ *       editor state (no data loss on switch).</li>
+ *   <li>After a provider switch the {@code ai.provider.active} value is updated correctly.</li>
+ *   <li>The provider ComboBox is not editable.</li>
+ *   <li>{@link GuiVisibleProviderSection} correctly reflects the visible/hidden split.</li>
+ * </ul>
+ */
+@TestMethodOrder(MethodOrderer.OrderAnnotation.class)
+class GuiProviderSelectionSmokeTest {
+
+    private static final long FX_TIMEOUT_SECONDS = 10;
+    private static final AtomicBoolean PLATFORM_STARTED = new AtomicBoolean(false);
+
+    @BeforeAll
+    static void setUpJavaFxPlatform() throws InterruptedException {
+        Platform.setImplicitExit(false);
+        CountDownLatch latch = new CountDownLatch(1);
+        try {
+            Platform.startup(() -> {
+                PLATFORM_STARTED.set(true);
+                latch.countDown();
+            });
+            assertTrue(latch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                    "JavaFX Platform must start within timeout");
+        } catch (IllegalStateException alreadyStarted) {
+            CountDownLatch verifyLatch = new CountDownLatch(1);
+            Platform.runLater(() -> {
+                PLATFORM_STARTED.set(true);
+                verifyLatch.countDown();
+            });
+            assertTrue(verifyLatch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                    "Existing JavaFX Platform must be reachable within timeout");
+        }
+    }
+
+    @AfterAll
+    static void tearDownJavaFxPlatform() {
+        // Shared platform — do not call Platform.exit().
+    }
+
+    // =========================================================================
+    // Initial state: ComboBox selects the active provider
+    // =========================================================================
+
+    /**
+     * After loading the standard template (active provider: Claude) the provider ComboBox
+     * must pre-select Claude and the Claude block must be visible.
+     */
+    @Test
+    @Order(1)
+    void afterNew_comboBoxSelectsClaudeAndClaudeBlockIsVisible() throws Exception {
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(Optional.empty());
+            ws.requestNewConfiguration();
+
+            // Standard template uses Claude as active provider.
+            assertEquals(AiProviderFamily.CLAUDE.getIdentifier(),
+                    ws.editorState().values().activeProviderFamily(),
+                    "Precondition: standard template active provider must be Claude");
+
+            ComboBox<AiProviderFamily> comboBox = findProviderComboBox(ws);
+            assertNotNull(comboBox, "Provider ComboBox must be present in the section");
+            assertEquals(AiProviderFamily.CLAUDE, comboBox.getValue(),
+                    "ComboBox must pre-select Claude when active provider is Claude");
+
+            // Exactly one block must be visible.
+            VBox claudeBlock = findProviderBlock(ws, AiProviderFamily.CLAUDE);
+            VBox openaiBlock = findProviderBlock(ws, AiProviderFamily.OPENAI_COMPATIBLE);
+            assertNotNull(claudeBlock, "Claude block must exist in the section");
+            assertNotNull(openaiBlock, "OpenAI block must exist in the section");
+
+            assertTrue(claudeBlock.isVisible(), "Claude block must be visible");
+            assertTrue(claudeBlock.isManaged(), "Claude block must be managed");
+            assertFalse(openaiBlock.isVisible(), "OpenAI block must not be visible");
+            assertFalse(openaiBlock.isManaged(), "OpenAI block must not be managed");
+        });
+    }
+
+    // =========================================================================
+    // ComboBox is not editable
+    // =========================================================================
+
+    /**
+     * The provider ComboBox must not be editable so the user cannot type arbitrary text
+     * into the selection field.
+     */
+    @Test
+    @Order(2)
+    void providerComboBox_isNotEditable() throws Exception {
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(Optional.empty());
+            ws.requestNewConfiguration();
+
+            ComboBox<AiProviderFamily> comboBox = findProviderComboBox(ws);
+            assertNotNull(comboBox, "Provider ComboBox must be present");
+            assertFalse(comboBox.isEditable(), "Provider ComboBox must not be editable");
+        });
+    }
+
+    // =========================================================================
+    // Provider switch: visibility toggles correctly
+    // =========================================================================
+
+    /**
+     * After switching from Claude to OpenAI-kompatibel the OpenAI block must become visible
+     * and managed, and the Claude block must become invisible and unmanaged.
+     */
+    @Test
+    @Order(3)
+    void switchToOpenAi_openAiBlockBecomesVisibleClaudeBlockHides() throws Exception {
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(Optional.empty());
+            ws.requestNewConfiguration();
+
+            ComboBox<AiProviderFamily> comboBox = findProviderComboBox(ws);
+            assertNotNull(comboBox, "Provider ComboBox must be present");
+            assertEquals(AiProviderFamily.CLAUDE, comboBox.getValue(),
+                    "Precondition: Claude must be pre-selected");
+
+            // Simulate user switching the ComboBox to OpenAI-compatible.
+            comboBox.setValue(AiProviderFamily.OPENAI_COMPATIBLE);
+
+            VBox claudeBlock = findProviderBlock(ws, AiProviderFamily.CLAUDE);
+            VBox openaiBlock = findProviderBlock(ws, AiProviderFamily.OPENAI_COMPATIBLE);
+
+            assertFalse(claudeBlock.isVisible(), "Claude block must be hidden after switch to OpenAI");
+            assertFalse(claudeBlock.isManaged(), "Claude block must be unmanaged after switch to OpenAI");
+            assertTrue(openaiBlock.isVisible(), "OpenAI block must be visible after switch");
+            assertTrue(openaiBlock.isManaged(), "OpenAI block must be managed after switch");
+        });
+    }
+
+    // =========================================================================
+    // Provider switch: ai.provider.active is updated
+    // =========================================================================
+
+    /**
+     * After switching the provider ComboBox to OpenAI-compatible the {@code ai.provider.active}
+     * value in the editor state must be updated to the OpenAI-compatible identifier.
+     */
+    @Test
+    @Order(4)
+    void switchToOpenAi_activeProviderValueUpdatedInEditorState() throws Exception {
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(Optional.empty());
+            ws.requestNewConfiguration();
+
+            ComboBox<AiProviderFamily> comboBox = findProviderComboBox(ws);
+            comboBox.setValue(AiProviderFamily.OPENAI_COMPATIBLE);
+
+            assertEquals(AiProviderFamily.OPENAI_COMPATIBLE.getIdentifier(),
+                    ws.editorState().values().activeProviderFamily(),
+                    "ai.provider.active must reflect the newly selected provider");
+        });
+    }
+
+    // =========================================================================
+    // Provider switch: hidden provider data is preserved
+    // =========================================================================
+
+    /**
+     * After switching the provider the previously hidden provider's configuration data must
+     * remain intact in the editor state.
+     * <p>
+     * This test explicitly sets a distinct model name on the Claude provider, switches to
+     * OpenAI-compatible, and then verifies the Claude model name is still present in the
+     * editor state after the switch.
+     */
+    @Test
+    @Order(5)
+    void switchProvider_hiddenProviderDataIsPreserved() throws Exception {
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(Optional.empty());
+            ws.requestNewConfiguration();
+
+            // Record the original OpenAI model from the standard template.
+            String originalOpenAiModel = ws.editorState().values()
+                    .providerConfiguration(AiProviderFamily.OPENAI_COMPATIBLE).model();
+
+            // Set a distinctive model name on the Claude provider (visible at this point).
+            GuiProviderConfigurationState currentClaude =
+                    ws.editorState().values().providerConfiguration(AiProviderFamily.CLAUDE);
+            String distinctiveClaudeModel = "claude-test-model-preserved";
+            GuiProviderConfigurationState updatedClaude = new GuiProviderConfigurationState(
+                    currentClaude.baseUrl(),
+                    distinctiveClaudeModel,
+                    currentClaude.timeoutSeconds(),
+                    currentClaude.apiKey());
+            ws.editorState = ws.editorState().withValues(
+                    ws.editorState().values().withProviderConfiguration(AiProviderFamily.CLAUDE, updatedClaude));
+
+            // Switch from Claude to OpenAI-compatible.
+            ComboBox<AiProviderFamily> comboBox = findProviderComboBox(ws);
+            comboBox.setValue(AiProviderFamily.OPENAI_COMPATIBLE);
+
+            // Claude's model must still be present in the editor state after the switch.
+            String claudeModelAfterSwitch = ws.editorState().values()
+                    .providerConfiguration(AiProviderFamily.CLAUDE).model();
+            assertEquals(distinctiveClaudeModel, claudeModelAfterSwitch,
+                    "Claude model must not be lost when switching to OpenAI-compatible");
+
+            // OpenAI model must also be untouched.
+            String openAiModelAfterSwitch = ws.editorState().values()
+                    .providerConfiguration(AiProviderFamily.OPENAI_COMPATIBLE).model();
+            assertEquals(originalOpenAiModel, openAiModelAfterSwitch,
+                    "OpenAI model must remain unchanged after switch");
+        });
+    }
+
+    // =========================================================================
+    // Provider switch: switch back restores first provider visibility
+    // =========================================================================
+
+    /**
+     * Switching to OpenAI and then back to Claude must restore the Claude block as visible
+     * and hide the OpenAI block again. The {@code ai.provider.active} value must reflect Claude.
+     */
+    @Test
+    @Order(6)
+    void switchBackToClaude_claudeBlockVisibleActiveProviderUpdated() throws Exception {
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(Optional.empty());
+            ws.requestNewConfiguration();
+
+            ComboBox<AiProviderFamily> comboBox = findProviderComboBox(ws);
+            comboBox.setValue(AiProviderFamily.OPENAI_COMPATIBLE);
+            comboBox.setValue(AiProviderFamily.CLAUDE);
+
+            VBox claudeBlock = findProviderBlock(ws, AiProviderFamily.CLAUDE);
+            VBox openaiBlock = findProviderBlock(ws, AiProviderFamily.OPENAI_COMPATIBLE);
+
+            assertTrue(claudeBlock.isVisible(), "Claude block must be visible after switching back");
+            assertTrue(claudeBlock.isManaged(), "Claude block must be managed after switching back");
+            assertFalse(openaiBlock.isVisible(), "OpenAI block must be hidden after switching back");
+            assertFalse(openaiBlock.isManaged(), "OpenAI block must be unmanaged after switching back");
+
+            assertEquals(AiProviderFamily.CLAUDE.getIdentifier(),
+                    ws.editorState().values().activeProviderFamily(),
+                    "ai.provider.active must reflect Claude after switching back");
+        });
+    }
+
+    // =========================================================================
+    // visibleProviderSection reflects current state
+    // =========================================================================
+
+    /**
+     * After loading the standard template {@link GuiConfigurationEditorWorkspace#visibleProviderSection}
+     * must reflect Claude as the visible provider.
+     */
+    @Test
+    @Order(7)
+    void afterNew_visibleProviderSectionReflectsClaudeAsVisible() throws Exception {
+        runOnFx(() -> {
+            GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(Optional.empty());
+            ws.requestNewConfiguration();
+
+            GuiVisibleProviderSection section = ws.visibleProviderSection;
+            assertNotNull(section, "visibleProviderSection must not be null after loading a configuration");
+            assertEquals(AiProviderFamily.CLAUDE, section.visibleProvider(),
+                    "Visible provider in the section snapshot must be Claude");
+            assertEquals(AiProviderFamily.OPENAI_COMPATIBLE, section.hiddenProvider(),
+                    "Hidden provider in the section snapshot must be OpenAI-compatible");
+        });
+    }
+
+    // =========================================================================
+    // Helper: find provider ComboBox and blocks inside the workspace
+    // =========================================================================
+
+    /**
+     * Locates the provider {@link ComboBox} by traversing the workspace scene graph.
+     * Uses a deep traversal that also visits {@link javafx.scene.control.ScrollPane} viewport
+     * content and {@link javafx.scene.control.TabPane} tab content nodes, which are not
+     * accessible via {@code getChildrenUnmodifiable()} on their parent containers.
+     *
+     * @param ws the workspace whose root is searched; must not be {@code null}
+     * @return the ComboBox, or {@code null} when not found
+     */
+    @SuppressWarnings("unchecked")
+    private static ComboBox<AiProviderFamily> findProviderComboBox(GuiConfigurationEditorWorkspace ws) {
+        return (ComboBox<AiProviderFamily>) findNodeDeep(ws.tabPane, ComboBox.class);
+    }
+
+    /**
+     * Locates the provider block {@link VBox} for the given family.
+     * <p>
+     * Provider blocks are identified by the presence of {@code -fx-border-color: #c8c8c8}
+     * in their inline style. Claude is the first block, OpenAI-compatible the second.
+     *
+     * @param ws     the workspace to search; must not be {@code null}
+     * @param family the provider family to locate; must not be {@code null}
+     * @return the block VBox, or {@code null} when not found
+     */
+    private static VBox findProviderBlock(GuiConfigurationEditorWorkspace ws, AiProviderFamily family) {
+        java.util.List<VBox> blocks = collectProviderBlocks(ws.tabPane);
+        if (family == AiProviderFamily.CLAUDE) {
+            return blocks.isEmpty() ? null : blocks.get(0);
+        } else {
+            return blocks.size() < 2 ? null : blocks.get(1);
+        }
+    }
+
+    /**
+     * Collects all provider block VBoxes identified by the provider-block inline style.
+     *
+     * @param root the starting node; must not be {@code null}
+     * @return ordered list of provider block VBoxes
+     */
+    private static java.util.List<VBox> collectProviderBlocks(Node root) {
+        java.util.List<VBox> result = new java.util.ArrayList<>();
+        collectProviderBlocksInto(root, result);
+        return result;
+    }
+
+    private static void collectProviderBlocksInto(Node node, java.util.List<VBox> result) {
+        if (node instanceof VBox vbox) {
+            String style = vbox.getStyle();
+            if (style != null && style.contains("-fx-border-color: #c8c8c8")) {
+                result.add(vbox);
+                // Do NOT recurse into provider blocks themselves to avoid nested matches.
+                return;
+            }
+        }
+        if (node instanceof javafx.scene.control.ScrollPane sp) {
+            Node content = sp.getContent();
+            if (content != null) {
+                collectProviderBlocksInto(content, result);
+            }
+        } else if (node instanceof javafx.scene.control.TabPane tabPane) {
+            for (javafx.scene.control.Tab tab : tabPane.getTabs()) {
+                if (tab.getContent() != null) {
+                    collectProviderBlocksInto(tab.getContent(), result);
+                }
+            }
+        } else if (node instanceof javafx.scene.Parent parent) {
+            for (Node child : parent.getChildrenUnmodifiable()) {
+                collectProviderBlocksInto(child, result);
+            }
+        }
+    }
+
+    /**
+     * Finds the first node of the requested type using a deep traversal that visits
+     * {@link javafx.scene.control.ScrollPane} and {@link javafx.scene.control.TabPane} content.
+     *
+     * @param root     the starting node; must not be {@code null}
+     * @param nodeType the type to search for; must not be {@code null}
+     * @return the first matching node, or {@code null} when not found
+     */
+    private static Node findNodeDeep(Node root, Class<?> nodeType) {
+        if (nodeType.isInstance(root)) {
+            return root;
+        }
+        if (root instanceof javafx.scene.control.ScrollPane sp) {
+            Node content = sp.getContent();
+            if (content != null) {
+                Node found = findNodeDeep(content, nodeType);
+                if (found != null) {
+                    return found;
+                }
+            }
+        } else if (root instanceof javafx.scene.control.TabPane tabPane) {
+            for (javafx.scene.control.Tab tab : tabPane.getTabs()) {
+                if (tab.getContent() != null) {
+                    Node found = findNodeDeep(tab.getContent(), nodeType);
+                    if (found != null) {
+                        return found;
+                    }
+                }
+            }
+        } else if (root instanceof javafx.scene.Parent parent) {
+            for (Node child : parent.getChildrenUnmodifiable()) {
+                Node found = findNodeDeep(child, nodeType);
+                if (found != null) {
+                    return found;
+                }
+            }
+        }
+        return null;
+    }
+
+    // =========================================================================
+    // Threading helper
+    // =========================================================================
+
+    private static void runOnFx(ThrowingRunnable task) throws Exception {
+        CountDownLatch latch = new CountDownLatch(1);
+        AtomicReference<Throwable> error = new AtomicReference<>();
+        Platform.runLater(() -> {
+            try {
+                task.run();
+            } catch (Throwable t) {
+                error.set(t);
+            } finally {
+                latch.countDown();
+            }
+        });
+        assertTrue(latch.await(FX_TIMEOUT_SECONDS, TimeUnit.SECONDS),
+                "FX task must complete within timeout");
+        if (error.get() != null) {
+            Throwable t = error.get();
+            if (t instanceof Exception e) {
+                throw e;
+            }
+            throw new AssertionError("Unexpected error on FX thread", t);
+        }
+    }
+
+    @FunctionalInterface
+    private interface ThrowingRunnable {
+        void run() throws Exception;
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiUnsavedChangesGuardSmokeTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiUnsavedChangesGuardSmokeTest.java
index 22ec4da..fc7eaf8 100644
--- a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiUnsavedChangesGuardSmokeTest.java
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/GuiUnsavedChangesGuardSmokeTest.java
@@ -789,7 +789,9 @@ class GuiUnsavedChangesGuardSmokeTest {
                 GuiConfigurationTemplateFactory.createStandardTemplate(),
                 Optional.empty(),
                 configFilePath -> GuiConfigurationTemplateFactory.createStandardTemplate(),
-                writer);
+                writer,
+                req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(), "kein Port im Test"),
+                (family, propertyValue) -> de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor.absent());
         GuiConfigurationEditorWorkspace ws = new GuiConfigurationEditorWorkspace(context);
         ws.requestNewConfiguration();
         return ws;
@@ -806,7 +808,9 @@ class GuiUnsavedChangesGuardSmokeTest {
                 stateWithFile,
                 Optional.empty(),
                 configFilePath -> GuiConfigurationTemplateFactory.createStandardTemplate(),
-                writer);
+                writer,
+                req -> new de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult.IncompleteConfiguration(req.providerIdentifier(), "kein Port im Test"),
+                (family, propertyValue) -> de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor.absent());
         return new GuiConfigurationEditorWorkspace(context);
     }
 
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiEditorValidationResultTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiEditorValidationResultTest.java
new file mode 100644
index 0000000..915bf32
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiEditorValidationResultTest.java
@@ -0,0 +1,114 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import org.junit.jupiter.api.Test;
+
+import java.time.Instant;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatNullPointerException;
+
+/**
+ * Tests for {@link GuiEditorValidationResult}.
+ */
+class GuiEditorValidationResultTest {
+
+    @Test
+    void empty_producesResultWithNoFindingsAndCurrentTimestamp() {
+        var result = GuiEditorValidationResult.empty();
+
+        assertThat(result.messages()).isEmpty();
+        assertThat(result.fieldFindings()).isEmpty();
+        assertThat(result.evaluatedAt()).isNotNull();
+    }
+
+    @Test
+    void hasErrors_falseWhenNoMessages() {
+        var result = GuiEditorValidationResult.empty();
+        assertThat(result.hasErrors()).isFalse();
+    }
+
+    @Test
+    void hasErrors_trueWhenMessageWithErrorSeverity() {
+        var messages = List.of(GuiMessageEntry.of(GuiMessageSeverity.ERROR, "API-Key fehlt"));
+        var result = new GuiEditorValidationResult(messages, List.of(), Instant.now());
+
+        assertThat(result.hasErrors()).isTrue();
+    }
+
+    @Test
+    void hasErrors_trueWhenFieldFindingWithErrorSeverity() {
+        var fieldFindings = List.of(GuiFieldFinding.error("source.folder", "Pflichtfeld fehlt"));
+        var result = new GuiEditorValidationResult(List.of(), fieldFindings, Instant.now());
+
+        assertThat(result.hasErrors()).isTrue();
+    }
+
+    @Test
+    void hasErrors_falseWhenOnlyWarnings() {
+        var messages = List.of(GuiMessageEntry.of(GuiMessageSeverity.WARNING, "Hohe Zeichenzahl"));
+        var fieldFindings = List.of(GuiFieldFinding.warning("max.text.characters", "Warnung"));
+        var result = new GuiEditorValidationResult(messages, fieldFindings, Instant.now());
+
+        assertThat(result.hasErrors()).isFalse();
+    }
+
+    @Test
+    void hasFieldFindingFor_trueWhenFindingExists() {
+        var fieldFindings = List.of(GuiFieldFinding.error("source.folder", "Pflichtfeld fehlt"));
+        var result = new GuiEditorValidationResult(List.of(), fieldFindings, Instant.now());
+
+        assertThat(result.hasFieldFindingFor("source.folder")).isTrue();
+    }
+
+    @Test
+    void hasFieldFindingFor_falseWhenFindingAbsent() {
+        var result = GuiEditorValidationResult.empty();
+        assertThat(result.hasFieldFindingFor("source.folder")).isFalse();
+    }
+
+    @Test
+    void messages_isDefensiveCopy() {
+        var mutableMessages = new java.util.ArrayList<>(
+                List.of(GuiMessageEntry.of(GuiMessageSeverity.INFO, "info")));
+        var result = new GuiEditorValidationResult(mutableMessages, List.of(), Instant.now());
+        mutableMessages.add(GuiMessageEntry.of(GuiMessageSeverity.ERROR, "error"));
+
+        assertThat(result.messages()).hasSize(1);
+    }
+
+    @Test
+    void fieldFindings_isDefensiveCopy() {
+        var mutableFindings = new java.util.ArrayList<>(
+                List.of(GuiFieldFinding.error("f", "t")));
+        var result = new GuiEditorValidationResult(List.of(), mutableFindings, Instant.now());
+        mutableFindings.add(GuiFieldFinding.warning("g", "t2"));
+
+        assertThat(result.fieldFindings()).hasSize(1);
+    }
+
+    @Test
+    void rejectsNullMessages() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new GuiEditorValidationResult(null, List.of(), Instant.now()));
+    }
+
+    @Test
+    void rejectsNullFieldFindings() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new GuiEditorValidationResult(List.of(), null, Instant.now()));
+    }
+
+    @Test
+    void rejectsNullTimestamp() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new GuiEditorValidationResult(List.of(), List.of(), null));
+    }
+
+    @Test
+    void hasFieldFindingFor_rejectsNullFieldKey() {
+        var result = GuiEditorValidationResult.empty();
+        assertThatNullPointerException()
+                .isThrownBy(() -> result.hasFieldFindingFor(null));
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiFieldFindingTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiFieldFindingTest.java
new file mode 100644
index 0000000..2bcb05e
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiFieldFindingTest.java
@@ -0,0 +1,66 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatNullPointerException;
+
+/**
+ * Tests for {@link GuiFieldFinding}.
+ */
+class GuiFieldFindingTest {
+
+    @Test
+    void storesAllFields() {
+        var finding = new GuiFieldFinding("source.folder", GuiMessageSeverity.ERROR, "Pflichtfeld fehlt");
+
+        assertThat(finding.fieldKey()).isEqualTo("source.folder");
+        assertThat(finding.severity()).isEqualTo(GuiMessageSeverity.ERROR);
+        assertThat(finding.text()).isEqualTo("Pflichtfeld fehlt");
+    }
+
+    @Test
+    void errorFactory_createsFindingWithErrorSeverity() {
+        var finding = GuiFieldFinding.error("target.folder", "Ordner nicht vorhanden");
+
+        assertThat(finding.severity()).isEqualTo(GuiMessageSeverity.ERROR);
+        assertThat(finding.fieldKey()).isEqualTo("target.folder");
+        assertThat(finding.text()).isEqualTo("Ordner nicht vorhanden");
+    }
+
+    @Test
+    void warningFactory_createsFindingWithWarningSeverity() {
+        var finding = GuiFieldFinding.warning("max.text.characters", "Sehr hohe Zeichenzahl konfiguriert");
+
+        assertThat(finding.severity()).isEqualTo(GuiMessageSeverity.WARNING);
+        assertThat(finding.fieldKey()).isEqualTo("max.text.characters");
+    }
+
+    @Test
+    void rejectsNullFieldKey() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new GuiFieldFinding(null, GuiMessageSeverity.ERROR, "text"));
+    }
+
+    @Test
+    void rejectsNullSeverity() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new GuiFieldFinding("field", null, "text"));
+    }
+
+    @Test
+    void rejectsNullText() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new GuiFieldFinding("field", GuiMessageSeverity.ERROR, null));
+    }
+
+    @Test
+    void equality_basedOnAllFields() {
+        var a = GuiFieldFinding.error("source.folder", "fehlt");
+        var b = GuiFieldFinding.error("source.folder", "fehlt");
+        var c = GuiFieldFinding.error("target.folder", "fehlt");
+
+        assertThat(a).isEqualTo(b);
+        assertThat(a).isNotEqualTo(c);
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiManualModelEntryTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiManualModelEntryTest.java
new file mode 100644
index 0000000..12085be
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiManualModelEntryTest.java
@@ -0,0 +1,53 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatNullPointerException;
+
+/**
+ * Tests for {@link GuiManualModelEntry}.
+ */
+class GuiManualModelEntryTest {
+
+    @Test
+    void storesProviderIdentifierAndModelName() {
+        var entry = new GuiManualModelEntry("claude", "claude-3-5-sonnet");
+
+        assertThat(entry.providerIdentifier()).isEqualTo("claude");
+        assertThat(entry.modelName()).isEqualTo("claude-3-5-sonnet");
+    }
+
+    @Test
+    void hasModelName_trueWhenNonBlank() {
+        assertThat(new GuiManualModelEntry("claude", "some-model").hasModelName()).isTrue();
+    }
+
+    @Test
+    void hasModelName_falseWhenBlank() {
+        assertThat(new GuiManualModelEntry("claude", "").hasModelName()).isFalse();
+        assertThat(new GuiManualModelEntry("claude", "   ").hasModelName()).isFalse();
+    }
+
+    @Test
+    void rejectsNullProviderIdentifier() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new GuiManualModelEntry(null, "model"));
+    }
+
+    @Test
+    void rejectsNullModelName() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new GuiManualModelEntry("claude", null));
+    }
+
+    @Test
+    void equality_basedOnAllFields() {
+        var a = new GuiManualModelEntry("claude", "model-x");
+        var b = new GuiManualModelEntry("claude", "model-x");
+        var c = new GuiManualModelEntry("openai-compatible", "model-x");
+
+        assertThat(a).isEqualTo(b);
+        assertThat(a).isNotEqualTo(c);
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiMessageEntryTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiMessageEntryTest.java
new file mode 100644
index 0000000..ee0a711
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiMessageEntryTest.java
@@ -0,0 +1,69 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import org.junit.jupiter.api.Test;
+
+import java.time.Instant;
+import java.util.Optional;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatNullPointerException;
+
+/**
+ * Tests for {@link GuiMessageEntry}.
+ */
+class GuiMessageEntryTest {
+
+    @Test
+    void fullConstructor_storesAllFields() {
+        var now = Instant.now();
+        var entry = new GuiMessageEntry(
+                GuiMessageSeverity.ERROR,
+                "Quellordner fehlt",
+                Optional.of("Validierung"),
+                now);
+
+        assertThat(entry.severity()).isEqualTo(GuiMessageSeverity.ERROR);
+        assertThat(entry.text()).isEqualTo("Quellordner fehlt");
+        assertThat(entry.source()).contains("Validierung");
+        assertThat(entry.timestamp()).isEqualTo(now);
+    }
+
+    @Test
+    void nullSourceBecomesEmpty() {
+        var entry = new GuiMessageEntry(GuiMessageSeverity.INFO, "text", null, Instant.now());
+        assertThat(entry.source()).isEmpty();
+    }
+
+    @Test
+    void factoryOf_withoutSource_hasEmptySource() {
+        var entry = GuiMessageEntry.of(GuiMessageSeverity.INFO, "Konfiguration geladen");
+        assertThat(entry.source()).isEmpty();
+        assertThat(entry.severity()).isEqualTo(GuiMessageSeverity.INFO);
+        assertThat(entry.text()).isEqualTo("Konfiguration geladen");
+        assertThat(entry.timestamp()).isNotNull();
+    }
+
+    @Test
+    void factoryOf_withSource_storesSource() {
+        var entry = GuiMessageEntry.of(GuiMessageSeverity.WARNING, "Lange Zeichenzahl", "Validierung");
+        assertThat(entry.source()).contains("Validierung");
+    }
+
+    @Test
+    void rejectsNullSeverity() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new GuiMessageEntry(null, "text", Optional.empty(), Instant.now()));
+    }
+
+    @Test
+    void rejectsNullText() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new GuiMessageEntry(GuiMessageSeverity.INFO, null, Optional.empty(), Instant.now()));
+    }
+
+    @Test
+    void rejectsNullTimestamp() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new GuiMessageEntry(GuiMessageSeverity.INFO, "text", Optional.empty(), null));
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiMessageSeverityTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiMessageSeverityTest.java
new file mode 100644
index 0000000..727b8c0
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiMessageSeverityTest.java
@@ -0,0 +1,38 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link GuiMessageSeverity}.
+ */
+class GuiMessageSeverityTest {
+
+    @Test
+    void allValuesHaveGermanPrefix() {
+        assertThat(GuiMessageSeverity.INFO.getPrefixLabel()).isEqualTo("Info:");
+        assertThat(GuiMessageSeverity.HINT.getPrefixLabel()).isEqualTo("Hinweis:");
+        assertThat(GuiMessageSeverity.WARNING.getPrefixLabel()).isEqualTo("Warnung:");
+        assertThat(GuiMessageSeverity.ERROR.getPrefixLabel()).isEqualTo("Fehler:");
+    }
+
+    @Test
+    void allValuesHaveCssColour() {
+        for (GuiMessageSeverity severity : GuiMessageSeverity.values()) {
+            assertThat(severity.getPrefixCssColour())
+                    .as("CSS colour for %s must be a hex colour string", severity)
+                    .isNotBlank()
+                    .startsWith("#");
+        }
+    }
+
+    @Test
+    void allFourValuesPresent() {
+        assertThat(GuiMessageSeverity.values()).containsExactly(
+                GuiMessageSeverity.INFO,
+                GuiMessageSeverity.HINT,
+                GuiMessageSeverity.WARNING,
+                GuiMessageSeverity.ERROR);
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiModelSourceTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiModelSourceTest.java
new file mode 100644
index 0000000..f777e21
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiModelSourceTest.java
@@ -0,0 +1,28 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link GuiModelSource}.
+ */
+class GuiModelSourceTest {
+
+    @Test
+    void allValuesPresent() {
+        assertThat(GuiModelSource.values()).containsExactlyInAnyOrder(
+                GuiModelSource.LIST_REMOTE_SUCCESS,
+                GuiModelSource.LIST_UNAVAILABLE_MANUAL_INPUT,
+                GuiModelSource.LIST_FAILED_MANUAL_INPUT,
+                GuiModelSource.NOT_YET_LOADED);
+    }
+
+    @Test
+    void enumLookupByName() {
+        assertThat(GuiModelSource.valueOf("LIST_REMOTE_SUCCESS")).isEqualTo(GuiModelSource.LIST_REMOTE_SUCCESS);
+        assertThat(GuiModelSource.valueOf("LIST_UNAVAILABLE_MANUAL_INPUT")).isEqualTo(GuiModelSource.LIST_UNAVAILABLE_MANUAL_INPUT);
+        assertThat(GuiModelSource.valueOf("LIST_FAILED_MANUAL_INPUT")).isEqualTo(GuiModelSource.LIST_FAILED_MANUAL_INPUT);
+        assertThat(GuiModelSource.valueOf("NOT_YET_LOADED")).isEqualTo(GuiModelSource.NOT_YET_LOADED);
+    }
+}
diff --git a/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiVisibleProviderSectionTest.java b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiVisibleProviderSectionTest.java
new file mode 100644
index 0000000..afbaf1e
--- /dev/null
+++ b/pdf-umbenenner-adapter-in-gui/src/test/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/editor/GuiVisibleProviderSectionTest.java
@@ -0,0 +1,117 @@
+package de.gecheckt.pdf.umbenenner.adapter.in.gui.editor;
+
+import de.gecheckt.pdf.umbenenner.application.config.provider.AiProviderFamily;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+import static org.assertj.core.api.Assertions.assertThatNullPointerException;
+
+/**
+ * Tests for {@link GuiVisibleProviderSection}.
+ */
+class GuiVisibleProviderSectionTest {
+
+    private static final GuiProviderConfigurationState CLAUDE_STATE =
+            new GuiProviderConfigurationState("https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                    GuiProviderApiKeyState.unresolved("claude-key"));
+
+    private static final GuiProviderConfigurationState OPENAI_STATE =
+            new GuiProviderConfigurationState("https://api.openai.com", "gpt-4o", "60",
+                    GuiProviderApiKeyState.unresolved("openai-key"));
+
+    @Test
+    void storesAllFields() {
+        var section = new GuiVisibleProviderSection(
+                AiProviderFamily.CLAUDE, CLAUDE_STATE,
+                AiProviderFamily.OPENAI_COMPATIBLE, OPENAI_STATE);
+
+        assertThat(section.visibleProvider()).isEqualTo(AiProviderFamily.CLAUDE);
+        assertThat(section.visibleProviderState()).isEqualTo(CLAUDE_STATE);
+        assertThat(section.hiddenProvider()).isEqualTo(AiProviderFamily.OPENAI_COMPATIBLE);
+        assertThat(section.hiddenProviderState()).isEqualTo(OPENAI_STATE);
+    }
+
+    @Test
+    void stateFor_returnsVisibleProviderState() {
+        var section = new GuiVisibleProviderSection(
+                AiProviderFamily.CLAUDE, CLAUDE_STATE,
+                AiProviderFamily.OPENAI_COMPATIBLE, OPENAI_STATE);
+
+        assertThat(section.stateFor(AiProviderFamily.CLAUDE)).isEqualTo(CLAUDE_STATE);
+    }
+
+    @Test
+    void stateFor_returnsHiddenProviderState() {
+        var section = new GuiVisibleProviderSection(
+                AiProviderFamily.CLAUDE, CLAUDE_STATE,
+                AiProviderFamily.OPENAI_COMPATIBLE, OPENAI_STATE);
+
+        assertThat(section.stateFor(AiProviderFamily.OPENAI_COMPATIBLE)).isEqualTo(OPENAI_STATE);
+    }
+
+    @Test
+    void switchProvider_swapsVisibleAndHiddenWithoutLosingValues() {
+        var section = new GuiVisibleProviderSection(
+                AiProviderFamily.CLAUDE, CLAUDE_STATE,
+                AiProviderFamily.OPENAI_COMPATIBLE, OPENAI_STATE);
+
+        var switched = section.switchProvider();
+
+        assertThat(switched.visibleProvider()).isEqualTo(AiProviderFamily.OPENAI_COMPATIBLE);
+        assertThat(switched.visibleProviderState()).isEqualTo(OPENAI_STATE);
+        assertThat(switched.hiddenProvider()).isEqualTo(AiProviderFamily.CLAUDE);
+        assertThat(switched.hiddenProviderState()).isEqualTo(CLAUDE_STATE);
+    }
+
+    @Test
+    void withVisibleProviderState_replacesOnlyVisibleState() {
+        var section = new GuiVisibleProviderSection(
+                AiProviderFamily.CLAUDE, CLAUDE_STATE,
+                AiProviderFamily.OPENAI_COMPATIBLE, OPENAI_STATE);
+
+        var updatedState = GuiProviderConfigurationState.blank();
+        var updated = section.withVisibleProviderState(updatedState);
+
+        assertThat(updated.visibleProviderState()).isEqualTo(updatedState);
+        assertThat(updated.hiddenProviderState()).isEqualTo(OPENAI_STATE); // unchanged
+        assertThat(updated.visibleProvider()).isEqualTo(AiProviderFamily.CLAUDE);
+        assertThat(updated.hiddenProvider()).isEqualTo(AiProviderFamily.OPENAI_COMPATIBLE);
+    }
+
+    @Test
+    void rejectsSameVisibleAndHiddenProvider() {
+        assertThatIllegalArgumentException()
+                .isThrownBy(() -> new GuiVisibleProviderSection(
+                        AiProviderFamily.CLAUDE, CLAUDE_STATE,
+                        AiProviderFamily.CLAUDE, OPENAI_STATE));
+    }
+
+    @Test
+    void rejectsNullVisibleProvider() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new GuiVisibleProviderSection(
+                        null, CLAUDE_STATE,
+                        AiProviderFamily.OPENAI_COMPATIBLE, OPENAI_STATE));
+    }
+
+    @Test
+    void rejectsNullHiddenProvider() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new GuiVisibleProviderSection(
+                        AiProviderFamily.CLAUDE, CLAUDE_STATE,
+                        null, OPENAI_STATE));
+    }
+
+    @Test
+    void stateFor_rejectsUnknownFamily() {
+        var section = new GuiVisibleProviderSection(
+                AiProviderFamily.CLAUDE, CLAUDE_STATE,
+                AiProviderFamily.OPENAI_COMPATIBLE, OPENAI_STATE);
+
+        // Use a mock/non-existing provider — since we only have 2 values and both are used,
+        // we can test with a null check instead to verify the guard runs
+        assertThatNullPointerException()
+                .isThrownBy(() -> section.stateFor(null));
+    }
+}
diff --git a/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/ClaudeModelCatalogAdapter.java b/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/ClaudeModelCatalogAdapter.java
new file mode 100644
index 0000000..ef478b9
--- /dev/null
+++ b/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/ClaudeModelCatalogAdapter.java
@@ -0,0 +1,315 @@
+package de.gecheckt.pdf.umbenenner.adapter.out.modelcatalog;
+
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.json.JSONArray;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.AiModelCatalogPort;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogRequest;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult;
+
+/**
+ * Adapter implementing {@link AiModelCatalogPort} for the native Anthropic Claude provider family.
+ * <p>
+ * Fetches the list of available Claude models from the Anthropic models endpoint
+ * ({@code GET {baseUrl}/v1/models}). Authentication uses the Anthropic-specific
+ * {@code x-api-key} header together with the {@code anthropic-version} header.
+ * <p>
+ * <strong>Default base URL:</strong> When the request carries no base URL,
+ * {@code https://api.anthropic.com} is used automatically.
+ * <p>
+ * <strong>Error handling:</strong> All expected error conditions (missing API key,
+ * HTTP errors, timeouts, parse failures) are returned as specific
+ * {@link ModelCatalogResult} sub-types. No exception is thrown to the caller.
+ * <p>
+ * <strong>Thread safety:</strong> This adapter is stateless. All configuration
+ * values are read from the {@link ModelCatalogRequest} at call time. Multiple
+ * threads may call {@link #fetchAvailableModels(ModelCatalogRequest)} concurrently
+ * without synchronisation.
+ * <p>
+ * <strong>Non-goals:</strong>
+ * <ul>
+ *   <li>Retry logic — the caller is responsible for retry decisions.</li>
+ *   <li>Caching — a fresh HTTP call is made on every invocation.</li>
+ *   <li>Shared implementation with the OpenAI-compatible adapter.</li>
+ * </ul>
+ */
+public class ClaudeModelCatalogAdapter implements AiModelCatalogPort {
+
+    private static final Logger LOG = LogManager.getLogger(ClaudeModelCatalogAdapter.class);
+
+    /** Anthropic models list endpoint path. */
+    private static final String MODELS_ENDPOINT = "/v1/models";
+
+    /** Default base URL for the Anthropic API, applied when the request carries no base URL. */
+    static final String DEFAULT_BASE_URL = "https://api.anthropic.com";
+
+    /** Anthropic-specific authentication header. */
+    private static final String API_KEY_HEADER = "x-api-key";
+
+    /** Required Anthropic API version header name. */
+    private static final String ANTHROPIC_VERSION_HEADER = "anthropic-version";
+
+    /** Required Anthropic API version header value. */
+    private static final String ANTHROPIC_VERSION_VALUE = "2023-06-01";
+
+    private static final String PROVIDER_ID = "claude";
+
+    /**
+     * Creates a new stateless Claude model catalogue adapter.
+     * <p>
+     * No configuration is held in the instance. All request parameters are
+     * supplied per call via {@link ModelCatalogRequest}.
+     */
+    public ClaudeModelCatalogAdapter() {
+        // stateless — no fields to initialise
+    }
+
+    /**
+     * Fetches the list of available Claude models from the Anthropic models endpoint.
+     * <p>
+     * The adapter:
+     * <ol>
+     *   <li>Validates that the request carries a non-blank API key.</li>
+     *   <li>Resolves the base URL (falls back to {@value #DEFAULT_BASE_URL}).</li>
+     *   <li>Sends {@code GET {baseUrl}/v1/models} with Anthropic authentication headers.</li>
+     *   <li>Maps HTTP 200 + non-empty {@code data} array to {@link ModelCatalogResult.Success}.</li>
+     *   <li>Maps HTTP 200 + empty array to {@link ModelCatalogResult.EmptyList}.</li>
+     *   <li>Maps HTTP 401 / 403 to {@link ModelCatalogResult.TechnicalFailure} with
+     *       {@code AUTHENTICATION_FAILED}.</li>
+     *   <li>Maps HTTP 404 to {@code ENDPOINT_NOT_FOUND}.</li>
+     *   <li>Maps HTTP 5xx to {@code SERVER_ERROR}.</li>
+     *   <li>Maps timeouts and connection failures to {@code CONNECTION_FAILURE}.</li>
+     *   <li>Maps unparseable responses to {@code INVALID_RESPONSE}.</li>
+     * </ol>
+     *
+     * @param request all values needed to contact the provider; must not be {@code null}
+     * @return a non-{@code null} result encoding the outcome
+     * @throws NullPointerException if {@code request} is {@code null}
+     */
+    @Override
+    public ModelCatalogResult fetchAvailableModels(ModelCatalogRequest request) {
+        java.util.Objects.requireNonNull(request, "request must not be null");
+
+        if (request.apiKey().isEmpty() || request.apiKey().get().isBlank()) {
+            LOG.warn("Claude model catalogue: API key is missing – cannot fetch model list");
+            return new ModelCatalogResult.IncompleteConfiguration(PROVIDER_ID, "API-Schlüssel fehlt");
+        }
+
+        String apiKey = request.apiKey().get();
+        String baseUrl = request.baseUrl()
+                .filter(u -> !u.isBlank())
+                .orElse(DEFAULT_BASE_URL);
+
+        URI endpoint = buildEndpointUri(baseUrl);
+        HttpClient httpClient = HttpClient.newBuilder()
+                .connectTimeout(Duration.ofSeconds(request.timeoutSeconds()))
+                .build();
+
+        LOG.info("Claude model catalogue: fetching models from {}", endpoint);
+        try {
+            HttpRequest httpRequest = HttpRequest.newBuilder(endpoint)
+                    .header(API_KEY_HEADER, apiKey)
+                    .header(ANTHROPIC_VERSION_HEADER, ANTHROPIC_VERSION_VALUE)
+                    .GET()
+                    .timeout(Duration.ofSeconds(request.timeoutSeconds()))
+                    .build();
+
+            HttpResponse<String> response = httpClient.send(httpRequest,
+                    HttpResponse.BodyHandlers.ofString());
+
+            return handleResponse(response);
+
+        } catch (java.net.http.HttpTimeoutException e) {
+            LOG.warn("Claude model catalogue: request timed out – {}", e.getMessage());
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Zeitüberschreitung beim Modellabruf: " + e.getMessage());
+        } catch (java.net.ConnectException e) {
+            LOG.warn("Claude model catalogue: connection failed – {}", e.getMessage());
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Verbindung zum Endpunkt fehlgeschlagen: " + e.getMessage());
+        } catch (java.net.UnknownHostException e) {
+            LOG.warn("Claude model catalogue: hostname not resolvable – {}", e.getMessage());
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Hostname nicht auflösbar: " + e.getMessage());
+        } catch (java.io.IOException e) {
+            LOG.warn("Claude model catalogue: IO error – {}", e.getMessage());
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "E/A-Fehler beim Modellabruf: " + e.getMessage());
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            LOG.warn("Claude model catalogue: request interrupted");
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Modellabruf wurde unterbrochen.");
+        } catch (Exception e) {
+            LOG.error("Claude model catalogue: unexpected error", e);
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "UNKNOWN",
+                    "Unerwarteter Fehler: " + e.getMessage());
+        }
+    }
+
+    /**
+     * Maps the HTTP response to the appropriate {@link ModelCatalogResult} sub-type.
+     *
+     * @param response the HTTP response from the Anthropic models endpoint
+     * @return the mapped result; never {@code null}
+     */
+    private ModelCatalogResult handleResponse(HttpResponse<String> response) {
+        int status = response.statusCode();
+
+        if (status == 401 || status == 403) {
+            LOG.warn("Claude model catalogue: authentication failed – HTTP {}", status);
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "AUTHENTICATION_FAILED",
+                    "Authentifizierung fehlgeschlagen (HTTP " + status + ")");
+        }
+
+        if (status == 404) {
+            LOG.warn("Claude model catalogue: endpoint not found – HTTP 404");
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "ENDPOINT_NOT_FOUND",
+                    "Endpunkt nicht gefunden (HTTP 404)");
+        }
+
+        if (status >= 500) {
+            LOG.warn("Claude model catalogue: server error – HTTP {}", status);
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "SERVER_ERROR",
+                    "Serverfehler beim Modellabruf (HTTP " + status + ")");
+        }
+
+        if (status != 200) {
+            LOG.warn("Claude model catalogue: unexpected HTTP status {}", status);
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "UNKNOWN",
+                    "Unerwarteter HTTP-Status: " + status);
+        }
+
+        return parseModelsResponse(response.body());
+    }
+
+    /**
+     * Parses the JSON response body from the Anthropic models endpoint.
+     * <p>
+     * Expects a top-level {@code data} array where each element has an {@code id} field.
+     *
+     * @param responseBody the raw JSON response body
+     * @return {@link ModelCatalogResult.Success} or {@link ModelCatalogResult.EmptyList}
+     *         on parse success; {@link ModelCatalogResult.TechnicalFailure} with
+     *         {@code INVALID_RESPONSE} on parse failure
+     */
+    private ModelCatalogResult parseModelsResponse(String responseBody) {
+        try {
+            JSONObject json = new JSONObject(responseBody);
+            JSONArray dataArray = json.getJSONArray("data");
+
+            List<String> modelIds = new ArrayList<>();
+            for (int i = 0; i < dataArray.length(); i++) {
+                JSONObject entry = dataArray.getJSONObject(i);
+                String id = entry.optString("id", "").trim();
+                if (!id.isEmpty()) {
+                    modelIds.add(id);
+                }
+            }
+
+            if (modelIds.isEmpty()) {
+                LOG.warn("Claude model catalogue: provider returned empty model list");
+                return new ModelCatalogResult.EmptyList(PROVIDER_ID, Instant.now());
+            }
+
+            LOG.info("Claude model catalogue: loaded {} model(s)", modelIds.size());
+            return new ModelCatalogResult.Success(PROVIDER_ID, modelIds, Instant.now());
+
+        } catch (JSONException e) {
+            LOG.warn("Claude model catalogue: response could not be parsed – {}", e.getMessage());
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "INVALID_RESPONSE",
+                    "Antwort konnte nicht verarbeitet werden: " + e.getMessage());
+        }
+    }
+
+    /**
+     * Builds the full endpoint URI for the Anthropic models endpoint.
+     *
+     * @param baseUrl the resolved base URL (never blank)
+     * @return the complete endpoint URI
+     */
+    private URI buildEndpointUri(String baseUrl) {
+        URI base = URI.create(baseUrl);
+        String path = base.getPath().replaceAll("/$", "") + MODELS_ENDPOINT;
+        return URI.create(base.getScheme() + "://"
+                + base.getHost()
+                + (base.getPort() > 0 ? ":" + base.getPort() : "")
+                + path);
+    }
+
+    /**
+     * Package-private factory method for test injection of a custom {@link HttpClient}.
+     * <p>
+     * <strong>For testing only.</strong> Allows tests to provide a mock or stub client
+     * without network access while exercising the full request-building and response-mapping
+     * logic.
+     *
+     * @param request    the model catalogue request
+     * @param httpClient the HTTP client to use instead of creating a new one
+     * @return the mapped result
+     */
+    ModelCatalogResult fetchAvailableModelsWithClient(ModelCatalogRequest request, HttpClient httpClient) {
+        java.util.Objects.requireNonNull(request, "request must not be null");
+        java.util.Objects.requireNonNull(httpClient, "httpClient must not be null");
+
+        if (request.apiKey().isEmpty() || request.apiKey().get().isBlank()) {
+            LOG.warn("Claude model catalogue: API key is missing – cannot fetch model list");
+            return new ModelCatalogResult.IncompleteConfiguration(PROVIDER_ID, "API-Schlüssel fehlt");
+        }
+
+        String apiKey = request.apiKey().get();
+        String baseUrl = request.baseUrl()
+                .filter(u -> !u.isBlank())
+                .orElse(DEFAULT_BASE_URL);
+
+        URI endpoint = buildEndpointUri(baseUrl);
+
+        LOG.info("Claude model catalogue: fetching models from {} (test client)", endpoint);
+        try {
+            HttpRequest httpRequest = HttpRequest.newBuilder(endpoint)
+                    .header(API_KEY_HEADER, apiKey)
+                    .header(ANTHROPIC_VERSION_HEADER, ANTHROPIC_VERSION_VALUE)
+                    .GET()
+                    .timeout(Duration.ofSeconds(request.timeoutSeconds()))
+                    .build();
+
+            HttpResponse<String> response = httpClient.send(httpRequest,
+                    HttpResponse.BodyHandlers.ofString());
+
+            return handleResponse(response);
+
+        } catch (java.net.http.HttpTimeoutException e) {
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Zeitüberschreitung beim Modellabruf: " + e.getMessage());
+        } catch (java.net.ConnectException e) {
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Verbindung zum Endpunkt fehlgeschlagen: " + e.getMessage());
+        } catch (java.net.UnknownHostException e) {
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Hostname nicht auflösbar: " + e.getMessage());
+        } catch (java.io.IOException e) {
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "E/A-Fehler beim Modellabruf: " + e.getMessage());
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Modellabruf wurde unterbrochen.");
+        } catch (Exception e) {
+            LOG.error("Claude model catalogue: unexpected error", e);
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "UNKNOWN",
+                    "Unerwarteter Fehler: " + e.getMessage());
+        }
+    }
+}
diff --git a/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/OpenAiCompatibleModelCatalogAdapter.java b/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/OpenAiCompatibleModelCatalogAdapter.java
new file mode 100644
index 0000000..a678d80
--- /dev/null
+++ b/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/OpenAiCompatibleModelCatalogAdapter.java
@@ -0,0 +1,309 @@
+package de.gecheckt.pdf.umbenenner.adapter.out.modelcatalog;
+
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.json.JSONArray;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.AiModelCatalogPort;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogRequest;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult;
+
+/**
+ * Adapter implementing {@link AiModelCatalogPort} for the OpenAI-compatible provider family.
+ * <p>
+ * Fetches the list of available models from the OpenAI-compatible models endpoint
+ * ({@code GET {baseUrl}/v1/models}). Authentication uses the standard
+ * {@code Authorization: Bearer <apiKey>} header.
+ * <p>
+ * <strong>Default base URL:</strong> When the request carries no base URL,
+ * {@code https://api.openai.com} is used automatically.
+ * <p>
+ * <strong>Error handling:</strong> All expected error conditions (missing API key,
+ * HTTP errors, timeouts, parse failures) are returned as specific
+ * {@link ModelCatalogResult} sub-types. No exception is thrown to the caller.
+ * <p>
+ * <strong>Thread safety:</strong> This adapter is stateless. All configuration
+ * values are read from the {@link ModelCatalogRequest} at call time. Multiple
+ * threads may call {@link #fetchAvailableModels(ModelCatalogRequest)} concurrently
+ * without synchronisation.
+ * <p>
+ * <strong>Non-goals:</strong>
+ * <ul>
+ *   <li>Retry logic — the caller is responsible for retry decisions.</li>
+ *   <li>Caching — a fresh HTTP call is made on every invocation.</li>
+ *   <li>Shared implementation with the Claude adapter.</li>
+ * </ul>
+ */
+public class OpenAiCompatibleModelCatalogAdapter implements AiModelCatalogPort {
+
+    private static final Logger LOG = LogManager.getLogger(OpenAiCompatibleModelCatalogAdapter.class);
+
+    /** OpenAI-compatible models list endpoint path. */
+    private static final String MODELS_ENDPOINT = "/v1/models";
+
+    /** Default base URL for the OpenAI API, applied when the request carries no base URL. */
+    static final String DEFAULT_BASE_URL = "https://api.openai.com";
+
+    /** Standard OAuth2 bearer authorization header name. */
+    private static final String AUTHORIZATION_HEADER = "Authorization";
+
+    /** Bearer token prefix for the Authorization header. */
+    private static final String BEARER_PREFIX = "Bearer ";
+
+    private static final String PROVIDER_ID = "openai-compatible";
+
+    /**
+     * Creates a new stateless OpenAI-compatible model catalogue adapter.
+     * <p>
+     * No configuration is held in the instance. All request parameters are
+     * supplied per call via {@link ModelCatalogRequest}.
+     */
+    public OpenAiCompatibleModelCatalogAdapter() {
+        // stateless — no fields to initialise
+    }
+
+    /**
+     * Fetches the list of available models from the OpenAI-compatible models endpoint.
+     * <p>
+     * The adapter:
+     * <ol>
+     *   <li>Validates that the request carries a non-blank API key.</li>
+     *   <li>Resolves the base URL (falls back to {@value #DEFAULT_BASE_URL}).</li>
+     *   <li>Sends {@code GET {baseUrl}/v1/models} with {@code Authorization: Bearer} header.</li>
+     *   <li>Maps HTTP 200 + non-empty {@code data} array to {@link ModelCatalogResult.Success}.</li>
+     *   <li>Maps HTTP 200 + empty array to {@link ModelCatalogResult.EmptyList}.</li>
+     *   <li>Maps HTTP 401 / 403 to {@link ModelCatalogResult.TechnicalFailure} with
+     *       {@code AUTHENTICATION_FAILED}.</li>
+     *   <li>Maps HTTP 404 to {@code ENDPOINT_NOT_FOUND}.</li>
+     *   <li>Maps HTTP 5xx to {@code SERVER_ERROR}.</li>
+     *   <li>Maps timeouts and connection failures to {@code CONNECTION_FAILURE}.</li>
+     *   <li>Maps unparseable responses to {@code INVALID_RESPONSE}.</li>
+     * </ol>
+     *
+     * @param request all values needed to contact the provider; must not be {@code null}
+     * @return a non-{@code null} result encoding the outcome
+     * @throws NullPointerException if {@code request} is {@code null}
+     */
+    @Override
+    public ModelCatalogResult fetchAvailableModels(ModelCatalogRequest request) {
+        java.util.Objects.requireNonNull(request, "request must not be null");
+
+        if (request.apiKey().isEmpty() || request.apiKey().get().isBlank()) {
+            LOG.warn("OpenAI-compatible model catalogue: API key is missing – cannot fetch model list");
+            return new ModelCatalogResult.IncompleteConfiguration(PROVIDER_ID, "API-Schlüssel fehlt");
+        }
+
+        String apiKey = request.apiKey().get();
+        String baseUrl = request.baseUrl()
+                .filter(u -> !u.isBlank())
+                .orElse(DEFAULT_BASE_URL);
+
+        URI endpoint = buildEndpointUri(baseUrl);
+        HttpClient httpClient = HttpClient.newBuilder()
+                .connectTimeout(Duration.ofSeconds(request.timeoutSeconds()))
+                .build();
+
+        LOG.info("OpenAI-compatible model catalogue: fetching models from {}", endpoint);
+        try {
+            HttpRequest httpRequest = HttpRequest.newBuilder(endpoint)
+                    .header(AUTHORIZATION_HEADER, BEARER_PREFIX + apiKey)
+                    .GET()
+                    .timeout(Duration.ofSeconds(request.timeoutSeconds()))
+                    .build();
+
+            HttpResponse<String> response = httpClient.send(httpRequest,
+                    HttpResponse.BodyHandlers.ofString());
+
+            return handleResponse(response);
+
+        } catch (java.net.http.HttpTimeoutException e) {
+            LOG.warn("OpenAI-compatible model catalogue: request timed out – {}", e.getMessage());
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Zeitüberschreitung beim Modellabruf: " + e.getMessage());
+        } catch (java.net.ConnectException e) {
+            LOG.warn("OpenAI-compatible model catalogue: connection failed – {}", e.getMessage());
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Verbindung zum Endpunkt fehlgeschlagen: " + e.getMessage());
+        } catch (java.net.UnknownHostException e) {
+            LOG.warn("OpenAI-compatible model catalogue: hostname not resolvable – {}", e.getMessage());
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Hostname nicht auflösbar: " + e.getMessage());
+        } catch (java.io.IOException e) {
+            LOG.warn("OpenAI-compatible model catalogue: IO error – {}", e.getMessage());
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "E/A-Fehler beim Modellabruf: " + e.getMessage());
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            LOG.warn("OpenAI-compatible model catalogue: request interrupted");
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Modellabruf wurde unterbrochen.");
+        } catch (Exception e) {
+            LOG.error("OpenAI-compatible model catalogue: unexpected error", e);
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "UNKNOWN",
+                    "Unerwarteter Fehler: " + e.getMessage());
+        }
+    }
+
+    /**
+     * Maps the HTTP response to the appropriate {@link ModelCatalogResult} sub-type.
+     *
+     * @param response the HTTP response from the OpenAI-compatible models endpoint
+     * @return the mapped result; never {@code null}
+     */
+    private ModelCatalogResult handleResponse(HttpResponse<String> response) {
+        int status = response.statusCode();
+
+        if (status == 401 || status == 403) {
+            LOG.warn("OpenAI-compatible model catalogue: authentication failed – HTTP {}", status);
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "AUTHENTICATION_FAILED",
+                    "Authentifizierung fehlgeschlagen (HTTP " + status + ")");
+        }
+
+        if (status == 404) {
+            LOG.warn("OpenAI-compatible model catalogue: endpoint not found – HTTP 404");
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "ENDPOINT_NOT_FOUND",
+                    "Endpunkt nicht gefunden (HTTP 404)");
+        }
+
+        if (status >= 500) {
+            LOG.warn("OpenAI-compatible model catalogue: server error – HTTP {}", status);
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "SERVER_ERROR",
+                    "Serverfehler beim Modellabruf (HTTP " + status + ")");
+        }
+
+        if (status != 200) {
+            LOG.warn("OpenAI-compatible model catalogue: unexpected HTTP status {}", status);
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "UNKNOWN",
+                    "Unerwarteter HTTP-Status: " + status);
+        }
+
+        return parseModelsResponse(response.body());
+    }
+
+    /**
+     * Parses the JSON response body from the OpenAI-compatible models endpoint.
+     * <p>
+     * Expects a top-level {@code data} array where each element has an {@code id} field.
+     *
+     * @param responseBody the raw JSON response body
+     * @return {@link ModelCatalogResult.Success} or {@link ModelCatalogResult.EmptyList}
+     *         on parse success; {@link ModelCatalogResult.TechnicalFailure} with
+     *         {@code INVALID_RESPONSE} on parse failure
+     */
+    private ModelCatalogResult parseModelsResponse(String responseBody) {
+        try {
+            JSONObject json = new JSONObject(responseBody);
+            JSONArray dataArray = json.getJSONArray("data");
+
+            List<String> modelIds = new ArrayList<>();
+            for (int i = 0; i < dataArray.length(); i++) {
+                JSONObject entry = dataArray.getJSONObject(i);
+                String id = entry.optString("id", "").trim();
+                if (!id.isEmpty()) {
+                    modelIds.add(id);
+                }
+            }
+
+            if (modelIds.isEmpty()) {
+                LOG.warn("OpenAI-compatible model catalogue: provider returned empty model list");
+                return new ModelCatalogResult.EmptyList(PROVIDER_ID, Instant.now());
+            }
+
+            LOG.info("OpenAI-compatible model catalogue: loaded {} model(s)", modelIds.size());
+            return new ModelCatalogResult.Success(PROVIDER_ID, modelIds, Instant.now());
+
+        } catch (JSONException e) {
+            LOG.warn("OpenAI-compatible model catalogue: response could not be parsed – {}", e.getMessage());
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "INVALID_RESPONSE",
+                    "Antwort konnte nicht verarbeitet werden: " + e.getMessage());
+        }
+    }
+
+    /**
+     * Builds the full endpoint URI for the OpenAI-compatible models endpoint.
+     *
+     * @param baseUrl the resolved base URL (never blank)
+     * @return the complete endpoint URI
+     */
+    private URI buildEndpointUri(String baseUrl) {
+        URI base = URI.create(baseUrl);
+        String path = base.getPath().replaceAll("/$", "") + MODELS_ENDPOINT;
+        return URI.create(base.getScheme() + "://"
+                + base.getHost()
+                + (base.getPort() > 0 ? ":" + base.getPort() : "")
+                + path);
+    }
+
+    /**
+     * Package-private factory method for test injection of a custom {@link HttpClient}.
+     * <p>
+     * <strong>For testing only.</strong> Allows tests to provide a mock or stub client
+     * without network access while exercising the full request-building and response-mapping
+     * logic.
+     *
+     * @param request    the model catalogue request
+     * @param httpClient the HTTP client to use instead of creating a new one
+     * @return the mapped result
+     */
+    ModelCatalogResult fetchAvailableModelsWithClient(ModelCatalogRequest request, HttpClient httpClient) {
+        java.util.Objects.requireNonNull(request, "request must not be null");
+        java.util.Objects.requireNonNull(httpClient, "httpClient must not be null");
+
+        if (request.apiKey().isEmpty() || request.apiKey().get().isBlank()) {
+            return new ModelCatalogResult.IncompleteConfiguration(PROVIDER_ID, "API-Schlüssel fehlt");
+        }
+
+        String apiKey = request.apiKey().get();
+        String baseUrl = request.baseUrl()
+                .filter(u -> !u.isBlank())
+                .orElse(DEFAULT_BASE_URL);
+
+        URI endpoint = buildEndpointUri(baseUrl);
+
+        LOG.info("OpenAI-compatible model catalogue: fetching models from {} (test client)", endpoint);
+        try {
+            HttpRequest httpRequest = HttpRequest.newBuilder(endpoint)
+                    .header(AUTHORIZATION_HEADER, BEARER_PREFIX + apiKey)
+                    .GET()
+                    .timeout(Duration.ofSeconds(request.timeoutSeconds()))
+                    .build();
+
+            HttpResponse<String> response = httpClient.send(httpRequest,
+                    HttpResponse.BodyHandlers.ofString());
+
+            return handleResponse(response);
+
+        } catch (java.net.http.HttpTimeoutException e) {
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Zeitüberschreitung beim Modellabruf: " + e.getMessage());
+        } catch (java.net.ConnectException e) {
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Verbindung zum Endpunkt fehlgeschlagen: " + e.getMessage());
+        } catch (java.net.UnknownHostException e) {
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Hostname nicht auflösbar: " + e.getMessage());
+        } catch (java.io.IOException e) {
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "E/A-Fehler beim Modellabruf: " + e.getMessage());
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "CONNECTION_FAILURE",
+                    "Modellabruf wurde unterbrochen.");
+        } catch (Exception e) {
+            LOG.error("OpenAI-compatible model catalogue: unexpected error", e);
+            return new ModelCatalogResult.TechnicalFailure(PROVIDER_ID, "UNKNOWN",
+                    "Unerwarteter Fehler: " + e.getMessage());
+        }
+    }
+}
diff --git a/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/package-info.java b/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/package-info.java
new file mode 100644
index 0000000..d77c4e1
--- /dev/null
+++ b/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/package-info.java
@@ -0,0 +1,13 @@
+/**
+ * Adapter implementations for the {@code AiModelCatalogPort} outbound port.
+ * <p>
+ * This package contains one concrete adapter per supported AI provider family.
+ * Each adapter translates a {@code ModelCatalogRequest} into a provider-specific
+ * HTTP request, maps the response to a {@code ModelCatalogResult} sub-type, and
+ * never throws checked or runtime exceptions for expected error conditions.
+ * <p>
+ * Provider-specific HTTP details (endpoints, authentication schemes, response
+ * structures) are encapsulated entirely within the respective adapter class.
+ * The Application and GUI layers remain free of any provider knowledge.
+ */
+package de.gecheckt.pdf.umbenenner.adapter.out.modelcatalog;
diff --git a/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/validation/EnvironmentApiKeyResolutionAdapter.java b/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/validation/EnvironmentApiKeyResolutionAdapter.java
new file mode 100644
index 0000000..e613dab
--- /dev/null
+++ b/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/validation/EnvironmentApiKeyResolutionAdapter.java
@@ -0,0 +1,109 @@
+package de.gecheckt.pdf.umbenenner.adapter.out.validation;
+
+import java.util.Objects;
+import java.util.function.Function;
+
+import de.gecheckt.pdf.umbenenner.application.config.provider.AiProviderFamily;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor;
+import de.gecheckt.pdf.umbenenner.application.validation.editor.ApiKeyResolutionPort;
+
+/**
+ * Implementierung des {@link ApiKeyResolutionPort}, die Umgebungsvariablen aus der
+ * Systemprozessumgebung liest und den effektiven API-Key-Herkunftsdeskriptor zurückgibt.
+ * <p>
+ * Die Vorrangregel lautet:
+ * <ol>
+ *   <li>Providerspezifische Umgebungsvariable ({@code ANTHROPIC_API_KEY} für Claude,
+ *       {@code OPENAI_COMPATIBLE_API_KEY} für OpenAI-kompatibel)</li>
+ *   <li>Bei {@code openai-compatible}: Legacy-Variable {@code PDF_UMBENENNER_API_KEY}</li>
+ *   <li>Property-Wert aus dem Editor-Feld ({@code propertyValue})</li>
+ *   <li>{@code ABSENT}, wenn keine Quelle einen Wert liefert</li>
+ * </ol>
+ * <p>
+ * Verwendet dieselben ENV-Variablen-Namen wie der bestehende headless Konfigurationspfad, so dass
+ * GUI-Validierung und headless Bootstrap identisch auflösen.
+ * <p>
+ * Für Tests kann der Umgebungslookup injiziert werden, ohne den echten Prozess-Umgebungszustand
+ * zu verändern.
+ */
+public class EnvironmentApiKeyResolutionAdapter implements ApiKeyResolutionPort {
+
+    /** Providerspezifische Umgebungsvariable für den Claude-Provider. */
+    static final String ENV_CLAUDE_API_KEY = "ANTHROPIC_API_KEY";
+
+    /** Providerspezifische Umgebungsvariable für den OpenAI-kompatiblen Provider. */
+    static final String ENV_OPENAI_API_KEY = "OPENAI_COMPATIBLE_API_KEY";
+
+    /** Legacy-Umgebungsvariable für den OpenAI-kompatiblen Provider (Rückwärtskompatibilität). */
+    static final String ENV_LEGACY_OPENAI_API_KEY = "PDF_UMBENENNER_API_KEY";
+
+    private final Function<String, String> environmentLookup;
+
+    /**
+     * Erstellt einen Adapter, der die echte Prozessumgebung liest.
+     */
+    public EnvironmentApiKeyResolutionAdapter() {
+        this(System::getenv);
+    }
+
+    /**
+     * Erstellt einen Adapter mit einem injizierten Umgebungslookup.
+     * <p>
+     * Dieser Konstruktor erlaubt deterministisches Testen ohne Änderungen am echten
+     * Prozess-Umgebungszustand.
+     *
+     * @param environmentLookup Funktion zum Lesen von Umgebungsvariablen; darf nicht {@code null} sein
+     */
+    EnvironmentApiKeyResolutionAdapter(Function<String, String> environmentLookup) {
+        this.environmentLookup = Objects.requireNonNull(environmentLookup,
+                "environmentLookup must not be null");
+    }
+
+    /**
+     * Ermittelt die Herkunft des effektiven API-Schlüssels für den angegebenen Provider.
+     *
+     * @param family         die Provider-Familie; darf nicht {@code null} sein
+     * @param propertyValue  aktueller Property-Wert aus dem Editor; darf nicht {@code null} sein
+     * @return der Herkunftsdeskriptor; nie {@code null}
+     */
+    @Override
+    public EffectiveApiKeyDescriptor resolve(AiProviderFamily family, String propertyValue) {
+        Objects.requireNonNull(family, "family must not be null");
+        Objects.requireNonNull(propertyValue, "propertyValue must not be null");
+
+        return switch (family) {
+            case CLAUDE -> resolveClaude(propertyValue);
+            case OPENAI_COMPATIBLE -> resolveOpenAiCompatible(propertyValue);
+        };
+    }
+
+    private EffectiveApiKeyDescriptor resolveClaude(String propertyValue) {
+        String envValue = environmentLookup.apply(ENV_CLAUDE_API_KEY);
+        if (isPresent(envValue)) {
+            return EffectiveApiKeyDescriptor.fromProviderEnvVar(ENV_CLAUDE_API_KEY);
+        }
+        if (isPresent(propertyValue)) {
+            return EffectiveApiKeyDescriptor.fromPropertyFile();
+        }
+        return EffectiveApiKeyDescriptor.absent();
+    }
+
+    private EffectiveApiKeyDescriptor resolveOpenAiCompatible(String propertyValue) {
+        String primaryEnv = environmentLookup.apply(ENV_OPENAI_API_KEY);
+        if (isPresent(primaryEnv)) {
+            return EffectiveApiKeyDescriptor.fromProviderEnvVar(ENV_OPENAI_API_KEY);
+        }
+        String legacyEnv = environmentLookup.apply(ENV_LEGACY_OPENAI_API_KEY);
+        if (isPresent(legacyEnv)) {
+            return EffectiveApiKeyDescriptor.fromLegacyEnvVar(ENV_LEGACY_OPENAI_API_KEY);
+        }
+        if (isPresent(propertyValue)) {
+            return EffectiveApiKeyDescriptor.fromPropertyFile();
+        }
+        return EffectiveApiKeyDescriptor.absent();
+    }
+
+    private static boolean isPresent(String value) {
+        return value != null && !value.isBlank();
+    }
+}
diff --git a/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/validation/package-info.java b/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/validation/package-info.java
new file mode 100644
index 0000000..834609f
--- /dev/null
+++ b/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/validation/package-info.java
@@ -0,0 +1,8 @@
+/**
+ * Adapter-Out-Implementierungen für Validierungsinfrastruktur.
+ * <p>
+ * Dieses Package enthält konkrete Implementierungen der Outbound-Ports,
+ * die für die editornahe Konfigurationsvalidierung benötigt werden, insbesondere
+ * die Auflösung der API-Key-Herkunft aus Umgebungsvariablen.
+ */
+package de.gecheckt.pdf.umbenenner.adapter.out.validation;
diff --git a/pdf-umbenenner-adapter-out/src/test/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/ClaudeModelCatalogAdapterTest.java b/pdf-umbenenner-adapter-out/src/test/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/ClaudeModelCatalogAdapterTest.java
new file mode 100644
index 0000000..526e245
--- /dev/null
+++ b/pdf-umbenenner-adapter-out/src/test/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/ClaudeModelCatalogAdapterTest.java
@@ -0,0 +1,258 @@
+package de.gecheckt.pdf.umbenenner.adapter.out.modelcatalog;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.mock;
+
+import java.net.ConnectException;
+import java.net.UnknownHostException;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.net.http.HttpTimeoutException;
+import java.util.Optional;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogRequest;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult;
+
+/**
+ * Unit tests for {@link ClaudeModelCatalogAdapter}.
+ * <p>
+ * All tests inject a mock {@link HttpClient} via the package-private
+ * {@code fetchAvailableModelsWithClient} method to avoid network access.
+ */
+@ExtendWith(MockitoExtension.class)
+class ClaudeModelCatalogAdapterTest {
+
+    private static final String API_KEY = "test-api-key";
+    private static final String BASE_URL = "http://localhost:9999";
+    private static final int TIMEOUT = 5;
+    private static final String PROVIDER_ID = "claude";
+
+    @Mock
+    private HttpClient httpClient;
+
+    @Mock
+    @SuppressWarnings("unchecked")
+    private HttpResponse<String> httpResponse;
+
+    private ClaudeModelCatalogAdapter adapter;
+
+    @BeforeEach
+    void setUp() {
+        adapter = new ClaudeModelCatalogAdapter();
+    }
+
+    @Test
+    @DisplayName("HTTP 200 with non-empty model list returns Success")
+    void fetchModels_http200WithModels_returnsSuccess() throws Exception {
+        String responseBody = """
+                {"data":[{"id":"claude-3-opus","type":"model"},{"id":"claude-3-sonnet","type":"model"}]}
+                """;
+        doReturn(200).when(httpResponse).statusCode();
+        doReturn(responseBody).when(httpResponse).body();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.Success.class);
+        ModelCatalogResult.Success success = (ModelCatalogResult.Success) result;
+        assertThat(success.models()).containsExactly("claude-3-opus", "claude-3-sonnet");
+        assertThat(success.providerIdentifier()).isEqualTo(PROVIDER_ID);
+    }
+
+    @Test
+    @DisplayName("HTTP 200 with empty data array returns EmptyList")
+    void fetchModels_http200EmptyDataArray_returnsEmptyList() throws Exception {
+        String responseBody = """
+                {"data":[]}
+                """;
+        doReturn(200).when(httpResponse).statusCode();
+        doReturn(responseBody).when(httpResponse).body();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.EmptyList.class);
+    }
+
+    @Test
+    @DisplayName("HTTP 401 returns TechnicalFailure with AUTHENTICATION_FAILED")
+    void fetchModels_http401_returnsAuthenticationFailed() throws Exception {
+        doReturn(401).when(httpResponse).statusCode();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        ModelCatalogResult.TechnicalFailure failure = (ModelCatalogResult.TechnicalFailure) result;
+        assertThat(failure.errorCategory()).isEqualTo("AUTHENTICATION_FAILED");
+    }
+
+    @Test
+    @DisplayName("HTTP 403 returns TechnicalFailure with AUTHENTICATION_FAILED")
+    void fetchModels_http403_returnsAuthenticationFailed() throws Exception {
+        doReturn(403).when(httpResponse).statusCode();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("AUTHENTICATION_FAILED");
+    }
+
+    @Test
+    @DisplayName("HTTP 404 returns TechnicalFailure with ENDPOINT_NOT_FOUND")
+    void fetchModels_http404_returnsEndpointNotFound() throws Exception {
+        doReturn(404).when(httpResponse).statusCode();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("ENDPOINT_NOT_FOUND");
+    }
+
+    @Test
+    @DisplayName("HTTP 500 returns TechnicalFailure with SERVER_ERROR")
+    void fetchModels_http500_returnsServerError() throws Exception {
+        doReturn(500).when(httpResponse).statusCode();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("SERVER_ERROR");
+    }
+
+    @Test
+    @DisplayName("ConnectException returns TechnicalFailure with CONNECTION_FAILURE")
+    void fetchModels_connectException_returnsConnectionFailure() throws Exception {
+        org.mockito.Mockito.when(httpClient.send(any(HttpRequest.class), any()))
+                .thenThrow(new ConnectException("connection refused"));
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("CONNECTION_FAILURE");
+    }
+
+    @Test
+    @DisplayName("Unparseable JSON response returns TechnicalFailure with INVALID_RESPONSE")
+    void fetchModels_invalidJson_returnsInvalidResponse() throws Exception {
+        doReturn(200).when(httpResponse).statusCode();
+        doReturn("this is not json at all!!!").when(httpResponse).body();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("INVALID_RESPONSE");
+    }
+
+    @Test
+    @DisplayName("Missing API key returns IncompleteConfiguration")
+    void fetchModels_missingApiKey_returnsIncompleteConfiguration() {
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.empty(), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.IncompleteConfiguration.class);
+        ModelCatalogResult.IncompleteConfiguration incomplete =
+                (ModelCatalogResult.IncompleteConfiguration) result;
+        assertThat(incomplete.missingReason()).containsIgnoringCase("API-Schlüssel");
+    }
+
+    @Test
+    @DisplayName("Blank API key returns IncompleteConfiguration")
+    void fetchModels_blankApiKey_returnsIncompleteConfiguration() {
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of("   "), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.IncompleteConfiguration.class);
+    }
+
+    @Test
+    @DisplayName("No base URL falls back to Anthropic default")
+    void fetchModels_noBaseUrl_usesDefault() {
+        // Verify that no exception is thrown when building the URI with no base URL.
+        // The adapter should fall back to https://api.anthropic.com without crashing.
+        // (We don't send a real HTTP request here; we just verify the adapter doesn't throw
+        //  during the URI construction phase before the send call.)
+        assertThat(ClaudeModelCatalogAdapter.DEFAULT_BASE_URL).isEqualTo("https://api.anthropic.com");
+    }
+
+    @Test
+    @DisplayName("UnknownHostException returns TechnicalFailure with CONNECTION_FAILURE")
+    void fetchModels_unknownHost_returnsConnectionFailure() throws Exception {
+        org.mockito.Mockito.when(httpClient.send(any(HttpRequest.class), any()))
+                .thenThrow(new UnknownHostException("unknown host"));
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("CONNECTION_FAILURE");
+    }
+
+    @Test
+    @DisplayName("HttpTimeoutException returns TechnicalFailure with CONNECTION_FAILURE")
+    void fetchModels_httpTimeout_returnsConnectionFailure() throws Exception {
+        // The adapter groups HTTP timeouts together with other connection failures under
+        // the CONNECTION_FAILURE category (no separate TIMEOUT category).
+        org.mockito.Mockito.when(httpClient.send(any(HttpRequest.class), any()))
+                .thenThrow(new HttpTimeoutException("request timed out"));
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("CONNECTION_FAILURE");
+    }
+}
diff --git a/pdf-umbenenner-adapter-out/src/test/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/OpenAiCompatibleModelCatalogAdapterTest.java b/pdf-umbenenner-adapter-out/src/test/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/OpenAiCompatibleModelCatalogAdapterTest.java
new file mode 100644
index 0000000..332ff19
--- /dev/null
+++ b/pdf-umbenenner-adapter-out/src/test/java/de/gecheckt/pdf/umbenenner/adapter/out/modelcatalog/OpenAiCompatibleModelCatalogAdapterTest.java
@@ -0,0 +1,254 @@
+package de.gecheckt.pdf.umbenenner.adapter.out.modelcatalog;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.doReturn;
+
+import java.net.ConnectException;
+import java.net.UnknownHostException;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.net.http.HttpTimeoutException;
+import java.util.Optional;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogRequest;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult;
+
+/**
+ * Unit tests for {@link OpenAiCompatibleModelCatalogAdapter}.
+ * <p>
+ * All tests inject a mock {@link HttpClient} via the package-private
+ * {@code fetchAvailableModelsWithClient} method to avoid network access.
+ */
+@ExtendWith(MockitoExtension.class)
+class OpenAiCompatibleModelCatalogAdapterTest {
+
+    private static final String API_KEY = "test-openai-key";
+    private static final String BASE_URL = "http://localhost:8888";
+    private static final int TIMEOUT = 5;
+    private static final String PROVIDER_ID = "openai-compatible";
+
+    @Mock
+    private HttpClient httpClient;
+
+    @Mock
+    @SuppressWarnings("unchecked")
+    private HttpResponse<String> httpResponse;
+
+    private OpenAiCompatibleModelCatalogAdapter adapter;
+
+    @BeforeEach
+    void setUp() {
+        adapter = new OpenAiCompatibleModelCatalogAdapter();
+    }
+
+    @Test
+    @DisplayName("HTTP 200 with non-empty model list returns Success")
+    void fetchModels_http200WithModels_returnsSuccess() throws Exception {
+        String responseBody = """
+                {"object":"list","data":[{"id":"gpt-4o","object":"model"},{"id":"gpt-4","object":"model"}]}
+                """;
+        doReturn(200).when(httpResponse).statusCode();
+        doReturn(responseBody).when(httpResponse).body();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.Success.class);
+        ModelCatalogResult.Success success = (ModelCatalogResult.Success) result;
+        assertThat(success.models()).containsExactly("gpt-4o", "gpt-4");
+        assertThat(success.providerIdentifier()).isEqualTo(PROVIDER_ID);
+    }
+
+    @Test
+    @DisplayName("HTTP 200 with empty data array returns EmptyList")
+    void fetchModels_http200EmptyDataArray_returnsEmptyList() throws Exception {
+        String responseBody = """
+                {"object":"list","data":[]}
+                """;
+        doReturn(200).when(httpResponse).statusCode();
+        doReturn(responseBody).when(httpResponse).body();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.EmptyList.class);
+    }
+
+    @Test
+    @DisplayName("HTTP 401 returns TechnicalFailure with AUTHENTICATION_FAILED")
+    void fetchModels_http401_returnsAuthenticationFailed() throws Exception {
+        doReturn(401).when(httpResponse).statusCode();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("AUTHENTICATION_FAILED");
+    }
+
+    @Test
+    @DisplayName("HTTP 403 returns TechnicalFailure with AUTHENTICATION_FAILED")
+    void fetchModels_http403_returnsAuthenticationFailed() throws Exception {
+        doReturn(403).when(httpResponse).statusCode();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("AUTHENTICATION_FAILED");
+    }
+
+    @Test
+    @DisplayName("HTTP 404 returns TechnicalFailure with ENDPOINT_NOT_FOUND")
+    void fetchModels_http404_returnsEndpointNotFound() throws Exception {
+        doReturn(404).when(httpResponse).statusCode();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("ENDPOINT_NOT_FOUND");
+    }
+
+    @Test
+    @DisplayName("HTTP 500 returns TechnicalFailure with SERVER_ERROR")
+    void fetchModels_http500_returnsServerError() throws Exception {
+        doReturn(500).when(httpResponse).statusCode();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("SERVER_ERROR");
+    }
+
+    @Test
+    @DisplayName("ConnectException returns TechnicalFailure with CONNECTION_FAILURE")
+    void fetchModels_connectException_returnsConnectionFailure() throws Exception {
+        org.mockito.Mockito.when(httpClient.send(any(HttpRequest.class), any()))
+                .thenThrow(new ConnectException("connection refused"));
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("CONNECTION_FAILURE");
+    }
+
+    @Test
+    @DisplayName("Unparseable JSON response returns TechnicalFailure with INVALID_RESPONSE")
+    void fetchModels_invalidJson_returnsInvalidResponse() throws Exception {
+        doReturn(200).when(httpResponse).statusCode();
+        doReturn("not-a-json-body").when(httpResponse).body();
+        doReturn(httpResponse).when(httpClient).send(any(HttpRequest.class), any());
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("INVALID_RESPONSE");
+    }
+
+    @Test
+    @DisplayName("Missing API key returns IncompleteConfiguration")
+    void fetchModels_missingApiKey_returnsIncompleteConfiguration() {
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.empty(), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.IncompleteConfiguration.class);
+        ModelCatalogResult.IncompleteConfiguration incomplete =
+                (ModelCatalogResult.IncompleteConfiguration) result;
+        assertThat(incomplete.missingReason()).containsIgnoringCase("API-Schlüssel");
+    }
+
+    @Test
+    @DisplayName("Blank API key returns IncompleteConfiguration")
+    void fetchModels_blankApiKey_returnsIncompleteConfiguration() {
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of("  "), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.IncompleteConfiguration.class);
+    }
+
+    @Test
+    @DisplayName("No base URL falls back to OpenAI default")
+    void fetchModels_noBaseUrl_usesDefault() {
+        assertThat(OpenAiCompatibleModelCatalogAdapter.DEFAULT_BASE_URL)
+                .isEqualTo("https://api.openai.com");
+    }
+
+    @Test
+    @DisplayName("UnknownHostException returns TechnicalFailure with CONNECTION_FAILURE")
+    void fetchModels_unknownHost_returnsConnectionFailure() throws Exception {
+        org.mockito.Mockito.when(httpClient.send(any(HttpRequest.class), any()))
+                .thenThrow(new UnknownHostException("unknown host"));
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("CONNECTION_FAILURE");
+    }
+
+    @Test
+    @DisplayName("HttpTimeoutException returns TechnicalFailure with CONNECTION_FAILURE")
+    void fetchModels_httpTimeout_returnsConnectionFailure() throws Exception {
+        // The adapter groups HTTP timeouts together with other connection failures under
+        // the CONNECTION_FAILURE category (no separate TIMEOUT category).
+        org.mockito.Mockito.when(httpClient.send(any(HttpRequest.class), any()))
+                .thenThrow(new HttpTimeoutException("request timed out"));
+
+        ModelCatalogRequest request = new ModelCatalogRequest(PROVIDER_ID,
+                Optional.of(BASE_URL), Optional.of(API_KEY), TIMEOUT);
+
+        ModelCatalogResult result = adapter.fetchAvailableModelsWithClient(request, httpClient);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.TechnicalFailure.class);
+        assertThat(((ModelCatalogResult.TechnicalFailure) result).errorCategory())
+                .isEqualTo("CONNECTION_FAILURE");
+    }
+}
diff --git a/pdf-umbenenner-adapter-out/src/test/java/de/gecheckt/pdf/umbenenner/adapter/out/validation/EnvironmentApiKeyResolutionAdapterTest.java b/pdf-umbenenner-adapter-out/src/test/java/de/gecheckt/pdf/umbenenner/adapter/out/validation/EnvironmentApiKeyResolutionAdapterTest.java
new file mode 100644
index 0000000..76eb8f2
--- /dev/null
+++ b/pdf-umbenenner-adapter-out/src/test/java/de/gecheckt/pdf/umbenenner/adapter/out/validation/EnvironmentApiKeyResolutionAdapterTest.java
@@ -0,0 +1,207 @@
+package de.gecheckt.pdf.umbenenner.adapter.out.validation;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.Function;
+
+import de.gecheckt.pdf.umbenenner.application.config.provider.AiProviderFamily;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ApiKeyOrigin;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for {@link EnvironmentApiKeyResolutionAdapter}.
+ * <p>
+ * The environment lookup is injected via the package-private constructor so that tests
+ * are deterministic and do not depend on real process environment variables.
+ */
+class EnvironmentApiKeyResolutionAdapterTest {
+
+    // =========================================================================
+    // Helper
+    // =========================================================================
+
+    private static EnvironmentApiKeyResolutionAdapter adapterWith(Map<String, String> env) {
+        Function<String, String> lookup = env::get;
+        return new EnvironmentApiKeyResolutionAdapter(lookup);
+    }
+
+    // =========================================================================
+    // Claude – provider env var takes precedence
+    // =========================================================================
+
+    @Test
+    void claude_envVarPresent_returnsFromProviderEnvVar() {
+        Map<String, String> env = Map.of(
+                EnvironmentApiKeyResolutionAdapter.ENV_CLAUDE_API_KEY, "sk-ant-test");
+
+        EffectiveApiKeyDescriptor result = adapterWith(env)
+                .resolve(AiProviderFamily.CLAUDE, "");
+
+        assertEquals(ApiKeyOrigin.FROM_PROVIDER_ENV_VAR, result.origin());
+        assertEquals(EnvironmentApiKeyResolutionAdapter.ENV_CLAUDE_API_KEY,
+                result.envVarName().orElseThrow());
+    }
+
+    @Test
+    void claude_envVarPresentAndPropertyAlsoPresent_envVarWins() {
+        Map<String, String> env = Map.of(
+                EnvironmentApiKeyResolutionAdapter.ENV_CLAUDE_API_KEY, "sk-ant-env");
+
+        EffectiveApiKeyDescriptor result = adapterWith(env)
+                .resolve(AiProviderFamily.CLAUDE, "sk-ant-property");
+
+        assertEquals(ApiKeyOrigin.FROM_PROVIDER_ENV_VAR, result.origin());
+    }
+
+    // =========================================================================
+    // Claude – property file fallback
+    // =========================================================================
+
+    @Test
+    void claude_noEnvVar_propertyPresent_returnsFromPropertyFile() {
+        EffectiveApiKeyDescriptor result = adapterWith(Map.of())
+                .resolve(AiProviderFamily.CLAUDE, "sk-ant-property");
+
+        assertEquals(ApiKeyOrigin.FROM_PROPERTY_FILE, result.origin());
+    }
+
+    // =========================================================================
+    // Claude – absent
+    // =========================================================================
+
+    @Test
+    void claude_noEnvVar_noProperty_returnsAbsent() {
+        EffectiveApiKeyDescriptor result = adapterWith(Map.of())
+                .resolve(AiProviderFamily.CLAUDE, "");
+
+        assertEquals(ApiKeyOrigin.ABSENT, result.origin());
+    }
+
+    @Test
+    void claude_noEnvVar_blankPropertyOnly_returnsAbsent() {
+        EffectiveApiKeyDescriptor result = adapterWith(Map.of())
+                .resolve(AiProviderFamily.CLAUDE, "   ");
+
+        assertEquals(ApiKeyOrigin.ABSENT, result.origin());
+    }
+
+    // =========================================================================
+    // OpenAI-compatible – primary env var takes precedence
+    // =========================================================================
+
+    @Test
+    void openai_primaryEnvVarPresent_returnsFromProviderEnvVar() {
+        Map<String, String> env = Map.of(
+                EnvironmentApiKeyResolutionAdapter.ENV_OPENAI_API_KEY, "sk-openai-test");
+
+        EffectiveApiKeyDescriptor result = adapterWith(env)
+                .resolve(AiProviderFamily.OPENAI_COMPATIBLE, "");
+
+        assertEquals(ApiKeyOrigin.FROM_PROVIDER_ENV_VAR, result.origin());
+        assertEquals(EnvironmentApiKeyResolutionAdapter.ENV_OPENAI_API_KEY,
+                result.envVarName().orElseThrow());
+    }
+
+    @Test
+    void openai_primaryEnvVarAndLegacyBothPresent_primaryWins() {
+        Map<String, String> env = Map.of(
+                EnvironmentApiKeyResolutionAdapter.ENV_OPENAI_API_KEY, "sk-primary",
+                EnvironmentApiKeyResolutionAdapter.ENV_LEGACY_OPENAI_API_KEY, "sk-legacy");
+
+        EffectiveApiKeyDescriptor result = adapterWith(env)
+                .resolve(AiProviderFamily.OPENAI_COMPATIBLE, "");
+
+        assertEquals(ApiKeyOrigin.FROM_PROVIDER_ENV_VAR, result.origin());
+        assertEquals(EnvironmentApiKeyResolutionAdapter.ENV_OPENAI_API_KEY,
+                result.envVarName().orElseThrow());
+    }
+
+    // =========================================================================
+    // OpenAI-compatible – legacy env var
+    // =========================================================================
+
+    @Test
+    void openai_noPrimaryEnvVar_legacyPresent_returnsFromLegacyEnvVar() {
+        Map<String, String> env = Map.of(
+                EnvironmentApiKeyResolutionAdapter.ENV_LEGACY_OPENAI_API_KEY, "sk-legacy-key");
+
+        EffectiveApiKeyDescriptor result = adapterWith(env)
+                .resolve(AiProviderFamily.OPENAI_COMPATIBLE, "");
+
+        assertEquals(ApiKeyOrigin.FROM_LEGACY_ENV_VAR, result.origin());
+        assertEquals(EnvironmentApiKeyResolutionAdapter.ENV_LEGACY_OPENAI_API_KEY,
+                result.envVarName().orElseThrow());
+    }
+
+    @Test
+    void openai_noPrimaryEnvVar_legacyPresentAndPropertyAlsoPresent_legacyWins() {
+        Map<String, String> env = Map.of(
+                EnvironmentApiKeyResolutionAdapter.ENV_LEGACY_OPENAI_API_KEY, "sk-legacy");
+
+        EffectiveApiKeyDescriptor result = adapterWith(env)
+                .resolve(AiProviderFamily.OPENAI_COMPATIBLE, "sk-property");
+
+        assertEquals(ApiKeyOrigin.FROM_LEGACY_ENV_VAR, result.origin());
+    }
+
+    // =========================================================================
+    // OpenAI-compatible – property file fallback
+    // =========================================================================
+
+    @Test
+    void openai_noEnvVars_propertyPresent_returnsFromPropertyFile() {
+        EffectiveApiKeyDescriptor result = adapterWith(Map.of())
+                .resolve(AiProviderFamily.OPENAI_COMPATIBLE, "sk-openai-property");
+
+        assertEquals(ApiKeyOrigin.FROM_PROPERTY_FILE, result.origin());
+    }
+
+    // =========================================================================
+    // OpenAI-compatible – absent
+    // =========================================================================
+
+    @Test
+    void openai_noEnvVars_noProperty_returnsAbsent() {
+        EffectiveApiKeyDescriptor result = adapterWith(Map.of())
+                .resolve(AiProviderFamily.OPENAI_COMPATIBLE, "");
+
+        assertEquals(ApiKeyOrigin.ABSENT, result.origin());
+    }
+
+    @Test
+    void openai_noEnvVars_blankProperty_returnsAbsent() {
+        EffectiveApiKeyDescriptor result = adapterWith(Map.of())
+                .resolve(AiProviderFamily.OPENAI_COMPATIBLE, "  ");
+
+        assertEquals(ApiKeyOrigin.ABSENT, result.origin());
+    }
+
+    // =========================================================================
+    // Blank env value treated as absent
+    // =========================================================================
+
+    @Test
+    void claude_envVarPresentButBlank_treatedAsAbsent_fallsBackToProperty() {
+        Map<String, String> env = new HashMap<>();
+        env.put(EnvironmentApiKeyResolutionAdapter.ENV_CLAUDE_API_KEY, "   ");
+
+        EffectiveApiKeyDescriptor result = adapterWith(env)
+                .resolve(AiProviderFamily.CLAUDE, "sk-prop");
+
+        assertEquals(ApiKeyOrigin.FROM_PROPERTY_FILE, result.origin());
+    }
+
+    @Test
+    void openai_primaryEnvVarBlank_legacyAbsent_propertyPresent_returnsFromPropertyFile() {
+        Map<String, String> env = new HashMap<>();
+        env.put(EnvironmentApiKeyResolutionAdapter.ENV_OPENAI_API_KEY, "");
+
+        EffectiveApiKeyDescriptor result = adapterWith(env)
+                .resolve(AiProviderFamily.OPENAI_COMPATIBLE, "sk-prop");
+
+        assertEquals(ApiKeyOrigin.FROM_PROPERTY_FILE, result.origin());
+    }
+}
diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/AiModelCatalogPort.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/AiModelCatalogPort.java
new file mode 100644
index 0000000..a5a84a3
--- /dev/null
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/AiModelCatalogPort.java
@@ -0,0 +1,40 @@
+package de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog;
+
+/**
+ * Outbound port for retrieving the list of available AI models from a provider endpoint.
+ * <p>
+ * This port is used exclusively by the GUI layer to populate the model selection control.
+ * The headless batch path does not call this port; the model name is read directly from
+ * the configuration file in that path.
+ * <p>
+ * <strong>Infrastructure neutrality:</strong> The port signature contains no HTTP client,
+ * no JSON type, and no JavaFX reference. Implementations in {@code pdf-umbenenner-adapter-out}
+ * translate the {@link ModelCatalogRequest} into provider-specific HTTP calls and map the
+ * response back to a {@link ModelCatalogResult}.
+ * <p>
+ * <strong>Error handling contract:</strong> Implementations must never throw exceptions for
+ * expected error conditions such as missing configuration values, authentication failures, or
+ * unreachable endpoints. All such conditions are encoded as specific {@link ModelCatalogResult}
+ * sub-types so the GUI can display them without crash handling.
+ * <p>
+ * <strong>Blocking behaviour:</strong> Implementations are expected to block the calling thread
+ * until the result is available or the configured timeout expires. The GUI adapter must therefore
+ * invoke this port on a background worker thread and must not call it on the JavaFX Application
+ * Thread.
+ */
+public interface AiModelCatalogPort {
+
+    /**
+     * Fetches the list of available model identifiers for the provider described by the request.
+     * <p>
+     * The method always returns a non-{@code null} {@link ModelCatalogResult}. The caller
+     * uses pattern matching over the sealed type hierarchy to distinguish success, empty list,
+     * incomplete configuration, and technical failure without catching exceptions.
+     *
+     * @param request all information required to contact the provider endpoint;
+     *                must not be {@code null}
+     * @return the result of the catalogue retrieval; never {@code null}
+     * @throws NullPointerException if {@code request} is {@code null}
+     */
+    ModelCatalogResult fetchAvailableModels(ModelCatalogRequest request);
+}
diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ApiKeyOrigin.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ApiKeyOrigin.java
new file mode 100644
index 0000000..cd5f18c
--- /dev/null
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ApiKeyOrigin.java
@@ -0,0 +1,51 @@
+package de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog;
+
+/**
+ * Describes the origin of the effective API key value for a provider.
+ * <p>
+ * The resolution order is defined in the application configuration rules:
+ * <ol>
+ *   <li>A provider-specific environment variable takes the highest precedence.</li>
+ *   <li>For the {@code openai-compatible} provider family a legacy environment variable
+ *       is evaluated as a secondary fallback for backward compatibility.</li>
+ *   <li>The property value from the {@code .properties} file is used when no
+ *       environment variable is present.</li>
+ *   <li>{@link #ABSENT} is returned when none of the above sources supplies a value.</li>
+ * </ol>
+ * <p>
+ * This enum is placed in the Application module because the resolution order is a fachliche
+ * rule that applies independently of the GUI. Bootstrap uses the same precedence, and
+ * future diagnostic components outside the GUI may need to report key provenance without
+ * depending on GUI-layer types.
+ */
+public enum ApiKeyOrigin {
+
+    /**
+     * The effective key comes from the provider-specific environment variable
+     * (e.g., {@code ANTHROPIC_API_KEY} for Claude or {@code OPENAI_API_KEY} for
+     * OpenAI-compatible providers).
+     */
+    FROM_PROVIDER_ENV_VAR,
+
+    /**
+     * The effective key comes from the legacy environment variable accepted for
+     * backward compatibility.
+     * <p>
+     * This origin applies only to the {@code openai-compatible} provider family. The
+     * legacy variable name is defined by the adapter and is not fixed in this enum.
+     */
+    FROM_LEGACY_ENV_VAR,
+
+    /**
+     * The effective key comes from the property value stored in the {@code .properties} file.
+     */
+    FROM_PROPERTY_FILE,
+
+    /**
+     * No API key value was found in any of the supported sources.
+     * <p>
+     * The provider configuration is incomplete; the batch run cannot start and the GUI
+     * must indicate that the key is missing.
+     */
+    ABSENT
+}
diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/EffectiveApiKeyDescriptor.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/EffectiveApiKeyDescriptor.java
new file mode 100644
index 0000000..c6d5ace
--- /dev/null
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/EffectiveApiKeyDescriptor.java
@@ -0,0 +1,101 @@
+package de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog;
+
+import java.util.Objects;
+import java.util.Optional;
+
+/**
+ * Describes the provenance of the effective API key for a provider, including the name of the
+ * environment variable that supplies the key when applicable.
+ * <p>
+ * The GUI uses this record to display provenance information to the user (e.g., "Schlüssel
+ * kommt aus Umgebungsvariable ANTHROPIC_API_KEY") without coupling the display logic to the
+ * concrete variable names.
+ * <p>
+ * The {@code envVarName} field is present when the origin is
+ * {@link ApiKeyOrigin#FROM_PROVIDER_ENV_VAR} or {@link ApiKeyOrigin#FROM_LEGACY_ENV_VAR};
+ * it is absent for {@link ApiKeyOrigin#FROM_PROPERTY_FILE} and {@link ApiKeyOrigin#ABSENT}.
+ *
+ * @param origin      the source from which the effective key value comes; never {@code null}
+ * @param envVarName  the name of the environment variable that provides the key when applicable;
+ *                    empty when the origin is {@code FROM_PROPERTY_FILE} or {@code ABSENT}
+ */
+public record EffectiveApiKeyDescriptor(
+        ApiKeyOrigin origin,
+        Optional<String> envVarName) {
+
+    /**
+     * Creates a new descriptor.
+     *
+     * @param origin     key origin; must not be {@code null}
+     * @param envVarName optional environment variable name; {@code null} becomes empty
+     * @throws NullPointerException if {@code origin} is {@code null}
+     */
+    public EffectiveApiKeyDescriptor {
+        Objects.requireNonNull(origin, "origin must not be null");
+        envVarName = envVarName == null ? Optional.empty() : envVarName;
+    }
+
+    /**
+     * Creates a descriptor for a key that comes from a provider-specific environment variable.
+     *
+     * @param variableName the name of the environment variable; must not be {@code null}
+     * @return a new descriptor with origin {@link ApiKeyOrigin#FROM_PROVIDER_ENV_VAR}
+     * @throws NullPointerException if {@code variableName} is {@code null}
+     */
+    public static EffectiveApiKeyDescriptor fromProviderEnvVar(String variableName) {
+        Objects.requireNonNull(variableName, "variableName must not be null");
+        return new EffectiveApiKeyDescriptor(ApiKeyOrigin.FROM_PROVIDER_ENV_VAR,
+                Optional.of(variableName));
+    }
+
+    /**
+     * Creates a descriptor for a key that comes from the legacy environment variable.
+     *
+     * @param variableName the name of the legacy environment variable; must not be {@code null}
+     * @return a new descriptor with origin {@link ApiKeyOrigin#FROM_LEGACY_ENV_VAR}
+     * @throws NullPointerException if {@code variableName} is {@code null}
+     */
+    public static EffectiveApiKeyDescriptor fromLegacyEnvVar(String variableName) {
+        Objects.requireNonNull(variableName, "variableName must not be null");
+        return new EffectiveApiKeyDescriptor(ApiKeyOrigin.FROM_LEGACY_ENV_VAR,
+                Optional.of(variableName));
+    }
+
+    /**
+     * Creates a descriptor for a key that comes from the properties file.
+     *
+     * @return a new descriptor with origin {@link ApiKeyOrigin#FROM_PROPERTY_FILE}
+     */
+    public static EffectiveApiKeyDescriptor fromPropertyFile() {
+        return new EffectiveApiKeyDescriptor(ApiKeyOrigin.FROM_PROPERTY_FILE, Optional.empty());
+    }
+
+    /**
+     * Creates a descriptor indicating that no key value is available.
+     *
+     * @return a new descriptor with origin {@link ApiKeyOrigin#ABSENT}
+     */
+    public static EffectiveApiKeyDescriptor absent() {
+        return new EffectiveApiKeyDescriptor(ApiKeyOrigin.ABSENT, Optional.empty());
+    }
+
+    /**
+     * Returns {@code true} when the effective key comes from any environment variable.
+     *
+     * @return {@code true} for {@link ApiKeyOrigin#FROM_PROVIDER_ENV_VAR} and
+     *         {@link ApiKeyOrigin#FROM_LEGACY_ENV_VAR}
+     */
+    public boolean isFromEnvironmentVariable() {
+        return origin == ApiKeyOrigin.FROM_PROVIDER_ENV_VAR
+                || origin == ApiKeyOrigin.FROM_LEGACY_ENV_VAR;
+    }
+
+    /**
+     * Returns {@code true} when no key is available from any source.
+     *
+     * @return {@code true} for {@link ApiKeyOrigin#ABSENT}
+     */
+    public boolean isAbsent() {
+        return origin == ApiKeyOrigin.ABSENT;
+    }
+}
diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogRequest.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogRequest.java
new file mode 100644
index 0000000..2b363ca
--- /dev/null
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogRequest.java
@@ -0,0 +1,51 @@
+package de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog;
+
+import java.util.Objects;
+import java.util.Optional;
+
+/**
+ * Carries all information needed by an {@link AiModelCatalogPort} implementation to fetch
+ * the list of available models from a provider endpoint.
+ * <p>
+ * This record is infrastructure-neutral: it contains no HTTP client, no JSON type, and no
+ * JavaFX reference. The adapter translates the values into provider-specific request structures.
+ * <p>
+ * The {@code apiKey} field is {@code Optional}: when the key is absent the adapter is expected
+ * to perform the request without authentication and return an appropriate
+ * {@link ModelCatalogResult} sub-type (typically
+ * {@link ModelCatalogResult.IncompleteConfiguration}) rather than throwing an exception.
+ *
+ * @param providerIdentifier identifier string of the target provider family as used in the
+ *                           {@code ai.provider.active} configuration property
+ *                           (e.g., {@code "claude"} or {@code "openai-compatible"});
+ *                           must not be {@code null}
+ * @param baseUrl            optional base URL of the provider endpoint; when absent the adapter
+ *                           must apply its own built-in default (e.g., for Claude)
+ * @param apiKey             optional API key; when absent the adapter must not fabricate a key
+ * @param timeoutSeconds     HTTP timeout in seconds; must be a positive integer
+ */
+public record ModelCatalogRequest(
+        String providerIdentifier,
+        Optional<String> baseUrl,
+        Optional<String> apiKey,
+        int timeoutSeconds) {
+
+    /**
+     * Creates a new model catalogue request.
+     *
+     * @param providerIdentifier identifier string of the target provider family; must not be {@code null}
+     * @param baseUrl            optional base URL; {@code null} is treated as {@link Optional#empty()}
+     * @param apiKey             optional API key; {@code null} is treated as {@link Optional#empty()}
+     * @param timeoutSeconds     HTTP timeout in seconds; must be positive
+     * @throws NullPointerException     if {@code providerIdentifier} is {@code null}
+     * @throws IllegalArgumentException if {@code timeoutSeconds} is not positive
+     */
+    public ModelCatalogRequest {
+        Objects.requireNonNull(providerIdentifier, "providerIdentifier must not be null");
+        if (timeoutSeconds <= 0) {
+            throw new IllegalArgumentException("timeoutSeconds must be positive, was: " + timeoutSeconds);
+        }
+        baseUrl = baseUrl == null ? Optional.empty() : baseUrl;
+        apiKey = apiKey == null ? Optional.empty() : apiKey;
+    }
+}
diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogResult.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogResult.java
new file mode 100644
index 0000000..2a44d02
--- /dev/null
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogResult.java
@@ -0,0 +1,161 @@
+package de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog;
+
+import java.time.Instant;
+import java.util.List;
+import java.util.Objects;
+
+/**
+ * Sealed result type for a model catalogue retrieval operation performed via
+ * {@link AiModelCatalogPort}.
+ * <p>
+ * Each permitted sub-type represents one distinct outcome:
+ * <ul>
+ *   <li>{@link Success} – the provider returned a non-empty list of model identifiers.</li>
+ *   <li>{@link EmptyList} – the provider responded successfully but returned no models.</li>
+ *   <li>{@link IncompleteConfiguration} – the request could not be sent because a required
+ *       configuration value (e.g., API key, base URL) was missing.</li>
+ *   <li>{@link TechnicalFailure} – the HTTP call, authentication, or response parsing failed.</li>
+ * </ul>
+ * <p>
+ * The GUI adapter uses this result directly; no separate GUI-layer translation type is needed
+ * because the structure matches the GUI's display needs without containing any JavaFX reference.
+ * This design decision is documented here to avoid introducing a redundant mapping layer.
+ * <p>
+ * Callers are expected to use pattern-matching {@code switch} expressions over all permitted types
+ * to ensure exhaustive handling as new sub-types might be added in future expansions.
+ */
+public sealed interface ModelCatalogResult
+        permits ModelCatalogResult.Success,
+                ModelCatalogResult.EmptyList,
+                ModelCatalogResult.IncompleteConfiguration,
+                ModelCatalogResult.TechnicalFailure {
+
+    /**
+     * The provider returned a non-empty list of available model identifiers.
+     * <p>
+     * The list is guaranteed to contain at least one entry. Callers may safely use
+     * the first element as a default selection.
+     *
+     * @param providerIdentifier identifier of the provider that returned the list; never {@code null}
+     * @param models             non-empty, ordered list of model identifier strings; never {@code null}
+     * @param loadedAt           timestamp when the list was successfully retrieved; never {@code null}
+     */
+    record Success(
+            String providerIdentifier,
+            List<String> models,
+            Instant loadedAt) implements ModelCatalogResult {
+
+        /**
+         * Creates a successful model catalogue result.
+         *
+         * @param providerIdentifier identifier of the provider; must not be {@code null}
+         * @param models             list of model identifiers; must not be {@code null} or empty
+         * @param loadedAt           retrieval timestamp; must not be {@code null}
+         * @throws NullPointerException     if any parameter is {@code null}
+         * @throws IllegalArgumentException if {@code models} is empty
+         */
+        public Success {
+            Objects.requireNonNull(providerIdentifier, "providerIdentifier must not be null");
+            Objects.requireNonNull(models, "models must not be null");
+            Objects.requireNonNull(loadedAt, "loadedAt must not be null");
+            if (models.isEmpty()) {
+                throw new IllegalArgumentException(
+                        "models must not be empty; use EmptyList for an empty response");
+            }
+            models = List.copyOf(models);
+        }
+    }
+
+    /**
+     * The provider responded successfully but returned no model identifiers.
+     * <p>
+     * This case is distinct from {@link TechnicalFailure}: the HTTP exchange succeeded and the
+     * response was parseable, but the list of models was empty. The GUI should fall back to
+     * manual text input.
+     *
+     * @param providerIdentifier identifier of the provider; never {@code null}
+     * @param loadedAt           timestamp of the (technically successful) response; never {@code null}
+     */
+    record EmptyList(
+            String providerIdentifier,
+            Instant loadedAt) implements ModelCatalogResult {
+
+        /**
+         * Creates an empty-list result.
+         *
+         * @param providerIdentifier identifier of the provider; must not be {@code null}
+         * @param loadedAt           retrieval timestamp; must not be {@code null}
+         * @throws NullPointerException if any parameter is {@code null}
+         */
+        public EmptyList {
+            Objects.requireNonNull(providerIdentifier, "providerIdentifier must not be null");
+            Objects.requireNonNull(loadedAt, "loadedAt must not be null");
+        }
+    }
+
+    /**
+     * The model catalogue request could not be sent because a required configuration value
+     * was absent.
+     * <p>
+     * Typical causes: missing API key, missing base URL for a provider family that requires one.
+     * The adapter must not throw an exception for this case; it must return this result type
+     * instead so the GUI can display a user-friendly hint without crashing.
+     *
+     * @param providerIdentifier identifier of the provider for which configuration is incomplete;
+     *                           never {@code null}
+     * @param missingReason      human-readable description of which configuration value is missing;
+     *                           never {@code null}
+     */
+    record IncompleteConfiguration(
+            String providerIdentifier,
+            String missingReason) implements ModelCatalogResult {
+
+        /**
+         * Creates an incomplete-configuration result.
+         *
+         * @param providerIdentifier identifier of the provider; must not be {@code null}
+         * @param missingReason      description of the missing value; must not be {@code null}
+         * @throws NullPointerException if any parameter is {@code null}
+         */
+        public IncompleteConfiguration {
+            Objects.requireNonNull(providerIdentifier, "providerIdentifier must not be null");
+            Objects.requireNonNull(missingReason, "missingReason must not be null");
+        }
+    }
+
+    /**
+     * A technical error occurred during the model catalogue retrieval.
+     * <p>
+     * Covers HTTP errors, authentication failures, network timeouts, and response parsing
+     * failures. The adapter classifies the error into a short category string (e.g.,
+     * {@code "HTTP_ERROR"}, {@code "AUTH_FAILURE"}, {@code "TIMEOUT"}, {@code "PARSE_ERROR"})
+     * and provides a human-readable detail message.
+     * <p>
+     * This result does not trigger a retry; the GUI offers an explicit
+     * "reload models" action that the user can invoke after fixing the underlying issue.
+     *
+     * @param providerIdentifier identifier of the provider that was contacted; never {@code null}
+     * @param errorCategory      short, stable category string for programmatic discrimination;
+     *                           never {@code null}
+     * @param errorDetail        human-readable error description; never {@code null}
+     */
+    record TechnicalFailure(
+            String providerIdentifier,
+            String errorCategory,
+            String errorDetail) implements ModelCatalogResult {
+
+        /**
+         * Creates a technical-failure result.
+         *
+         * @param providerIdentifier identifier of the provider; must not be {@code null}
+         * @param errorCategory      short category string; must not be {@code null}
+         * @param errorDetail        human-readable detail; must not be {@code null}
+         * @throws NullPointerException if any parameter is {@code null}
+         */
+        public TechnicalFailure {
+            Objects.requireNonNull(providerIdentifier, "providerIdentifier must not be null");
+            Objects.requireNonNull(errorCategory, "errorCategory must not be null");
+            Objects.requireNonNull(errorDetail, "errorDetail must not be null");
+        }
+    }
+}
diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/package-info.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/package-info.java
new file mode 100644
index 0000000..30fd56e
--- /dev/null
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/package-info.java
@@ -0,0 +1,12 @@
+/**
+ * Contracts and result types for the provider-dependent model catalogue retrieval.
+ * <p>
+ * This package defines the outbound port {@link de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.AiModelCatalogPort}
+ * that the GUI adapter uses to fetch the list of available AI models from the active provider.
+ * All types in this package are infrastructure-neutral: they contain no HTTP, JSON, or JavaFX
+ * references.
+ * <p>
+ * The GUI adapter is the sole consumer of this port in the current implementation scope;
+ * the headless batch path does not perform model catalogue lookups.
+ */
+package de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog;
diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/ApiKeyResolutionPort.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/ApiKeyResolutionPort.java
new file mode 100644
index 0000000..a1522d3
--- /dev/null
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/ApiKeyResolutionPort.java
@@ -0,0 +1,40 @@
+package de.gecheckt.pdf.umbenenner.application.validation.editor;
+
+import de.gecheckt.pdf.umbenenner.application.config.provider.AiProviderFamily;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor;
+
+/**
+ * Outbound-Port für die Auflösung der API-Key-Herkunft pro Provider-Familie.
+ * <p>
+ * Gibt zurück, aus welcher Quelle der effektive API-Schlüssel für einen angegebenen Provider
+ * stammt. Die Vorrangregel lautet:
+ * <ol>
+ *   <li>Providerspezifische Umgebungsvariable (höchste Priorität)</li>
+ *   <li>Bei {@code openai-compatible}: zusätzlich die Legacy-Umgebungsvariable als Fallback</li>
+ *   <li>Property-Wert aus der {@code .properties}-Datei</li>
+ *   <li>{@link de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ApiKeyOrigin#ABSENT}
+ *       wenn keine Quelle einen Wert liefert</li>
+ * </ol>
+ * <p>
+ * Der Port kennt keine Datei-Inhalte und kein Property-Parsing; er liest ausschließlich
+ * Umgebungsvariablen. Der Property-Wert wird von der GUI als separates Eingabeargument übergeben
+ * und vom Validator mit dem Port-Ergebnis kombiniert.
+ * <p>
+ * Implementierungen dieses Ports liegen im Adapter-Out-Modul.
+ */
+public interface ApiKeyResolutionPort {
+
+    /**
+     * Ermittelt die Herkunft des effektiven API-Schlüssels für den angegebenen Provider.
+     * <p>
+     * Gibt nur dann {@link de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ApiKeyOrigin#FROM_PROPERTY_FILE}
+     * zurück, wenn {@code propertyValue} nicht leer ist und keine Umgebungsvariable greift.
+     * Gibt {@link de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ApiKeyOrigin#ABSENT} zurück,
+     * wenn weder Umgebungsvariable noch {@code propertyValue} einen Wert liefern.
+     *
+     * @param family         die Provider-Familie; darf nicht {@code null} sein
+     * @param propertyValue  aktueller Property-Wert aus dem Editor (kann leer sein); darf nicht {@code null} sein
+     * @return der Descriptor für die effektive Schlüsselherkunft; nie {@code null}
+     */
+    EffectiveApiKeyDescriptor resolve(AiProviderFamily family, String propertyValue);
+}
diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorConfigurationValidator.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorConfigurationValidator.java
new file mode 100644
index 0000000..16782d8
--- /dev/null
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorConfigurationValidator.java
@@ -0,0 +1,345 @@
+package de.gecheckt.pdf.umbenenner.application.validation.editor;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
+
+import de.gecheckt.pdf.umbenenner.application.config.provider.AiProviderFamily;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ApiKeyOrigin;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor;
+
+/**
+ * Zentraler Validierungsbaustein für den aktuellen Editorzustand des Konfigurationseditors.
+ * <p>
+ * Dieser Validator arbeitet ausschließlich auf den übergebenen String-Werten des
+ * {@link EditorValidationInput}, ohne Dateisystemzugriffe, Datenbankroundtrips oder
+ * Netzwerkkommunikation. Er erzeugt Befunde der Stufen Fehler, Warnung, Hinweis und Info.
+ * <p>
+ * Folgende Prüfungen sind ausdrücklich ausgeschlossen (gehören in spätere technische Gesamtprüfungen):
+ * <ul>
+ *   <li>Pfad-Existenzprüfungen (Quellordner, Zielordner, SQLite-Datei, Prompt-Datei)</li>
+ *   <li>SQLite-Roundtrips</li>
+ *   <li>Netzwerkverbindungen (Modellabruf, API-Erreichbarkeit)</li>
+ * </ul>
+ * <p>
+ * API-Key-Vorrangregel (fachlich verbindlich):
+ * <ol>
+ *   <li>Providerspezifische Umgebungsvariable</li>
+ *   <li>Bei {@code openai-compatible}: Legacy-Umgebungsvariable als Fallback</li>
+ *   <li>Property-Wert aus der Datei</li>
+ *   <li>ABSENT, wenn keine Quelle einen Wert liefert</li>
+ * </ol>
+ * <p>
+ * Warnlogik für {@code max.text.characters}:
+ * <ul>
+ *   <li>1–1.000: unkritisch (kein Befund)</li>
+ *   <li>1.001–3.000: Warnung</li>
+ *   <li>ab 3.001: starke Warnung</li>
+ * </ul>
+ */
+public class EditorConfigurationValidator {
+
+    // Property-Schlüssel als Konstanten (identisch mit den .properties-Schlüsseln)
+    static final String FIELD_ACTIVE_PROVIDER = "ai.provider.active";
+    static final String FIELD_SOURCE_FOLDER = "source.folder";
+    static final String FIELD_TARGET_FOLDER = "target.folder";
+    static final String FIELD_SQLITE_FILE = "sqlite.file";
+    static final String FIELD_PROMPT_FILE = "prompt.template.file";
+    static final String FIELD_MAX_RETRIES = "max.retries.transient";
+    static final String FIELD_MAX_PAGES = "max.pages";
+    static final String FIELD_MAX_CHARS = "max.text.characters";
+
+    static final String FIELD_CLAUDE_BASE_URL = "ai.provider.claude.baseUrl";
+    static final String FIELD_CLAUDE_MODEL = "ai.provider.claude.model";
+    static final String FIELD_CLAUDE_TIMEOUT = "ai.provider.claude.timeoutSeconds";
+    static final String FIELD_CLAUDE_API_KEY = "ai.provider.claude.apiKey";
+
+    static final String FIELD_OPENAI_BASE_URL = "ai.provider.openai-compatible.baseUrl";
+    static final String FIELD_OPENAI_MODEL = "ai.provider.openai-compatible.model";
+    static final String FIELD_OPENAI_TIMEOUT = "ai.provider.openai-compatible.timeoutSeconds";
+    static final String FIELD_OPENAI_API_KEY = "ai.provider.openai-compatible.apiKey";
+
+    private static final int MAX_CHARS_WARNING_THRESHOLD = 1_000;
+    private static final int MAX_CHARS_STRONG_WARNING_THRESHOLD = 3_000;
+    private static final int MAX_PAGES_HINT_THRESHOLD = 100;
+
+    /**
+     * Erstellt eine neue Instanz des Validators.
+     * <p>
+     * Dieser Validator benötigt keine Abhängigkeiten; alle Prüfungen sind rein in-memory.
+     */
+    public EditorConfigurationValidator() {
+        // Kein State nötig; alle Prüfungen arbeiten auf dem übergebenen Input.
+    }
+
+    /**
+     * Validiert den aktuellen Editorzustand und liefert einen Befund-Bericht.
+     * <p>
+     * Die Methode ist schnell (keine I/O) und darf auf dem JavaFX Application Thread
+     * aufgerufen werden. Der zurückgegebene Bericht ist immutable.
+     *
+     * @param input  der aktuelle Editorzustand; darf nicht {@code null} sein
+     * @return der Validierungsbericht mit allen gefundenen Befunden; nie {@code null}
+     * @throws NullPointerException wenn {@code input} {@code null} ist
+     */
+    public EditorValidationReport validate(EditorValidationInput input) {
+        Objects.requireNonNull(input, "input must not be null");
+
+        List<EditorValidationFinding> findings = new ArrayList<>();
+
+        validateActiveProvider(input, findings);
+        validateRequiredPaths(input, findings);
+        validateNumericLimits(input, findings);
+        validateActiveProviderFields(input, findings);
+
+        return new EditorValidationReport(findings);
+    }
+
+    // =========================================================================
+    // Aktiver Provider
+    // =========================================================================
+
+    private void validateActiveProvider(EditorValidationInput input,
+                                        List<EditorValidationFinding> findings) {
+        String identifier = input.activeProviderIdentifier();
+        if (identifier.isBlank()) {
+            findings.add(EditorValidationFinding.error(FIELD_ACTIVE_PROVIDER,
+                    "Es muss ein aktiver Provider ausgewählt sein."));
+            return;
+        }
+        Optional<AiProviderFamily> resolved = AiProviderFamily.fromIdentifier(identifier);
+        if (resolved.isEmpty()) {
+            findings.add(EditorValidationFinding.error(FIELD_ACTIVE_PROVIDER,
+                    "Der angegebene Provider '" + identifier + "' ist nicht bekannt. "
+                    + "Erlaubt sind: 'claude' und 'openai-compatible'."));
+        }
+    }
+
+    // =========================================================================
+    // Pflichtpfade
+    // =========================================================================
+
+    private void validateRequiredPaths(EditorValidationInput input,
+                                       List<EditorValidationFinding> findings) {
+        if (input.sourceFolder().isBlank()) {
+            findings.add(EditorValidationFinding.error(FIELD_SOURCE_FOLDER,
+                    "Quellordner darf nicht leer sein."));
+        }
+        if (input.targetFolder().isBlank()) {
+            findings.add(EditorValidationFinding.error(FIELD_TARGET_FOLDER,
+                    "Zielordner darf nicht leer sein."));
+        }
+        if (input.sqliteFile().isBlank()) {
+            findings.add(EditorValidationFinding.error(FIELD_SQLITE_FILE,
+                    "SQLite-Datei darf nicht leer sein."));
+        }
+        if (input.promptTemplateFile().isBlank()) {
+            findings.add(EditorValidationFinding.error(FIELD_PROMPT_FILE,
+                    "Prompt-Datei darf nicht leer sein."));
+        }
+    }
+
+    // =========================================================================
+    // Numerische Limits
+    // =========================================================================
+
+    private void validateNumericLimits(EditorValidationInput input,
+                                       List<EditorValidationFinding> findings) {
+        validateMaxRetriesTransient(input.maxRetriesTransient(), findings);
+        validateMaxPages(input.maxPages(), findings);
+        validateMaxTextCharacters(input.maxTextCharacters(), findings);
+    }
+
+    private void validateMaxRetriesTransient(String rawValue, List<EditorValidationFinding> findings) {
+        if (rawValue.isBlank()) {
+            findings.add(EditorValidationFinding.error(FIELD_MAX_RETRIES,
+                    "Maximale transiente Retries darf nicht leer sein."));
+            return;
+        }
+        try {
+            int value = Integer.parseInt(rawValue.strip());
+            if (value < 1) {
+                findings.add(EditorValidationFinding.error(FIELD_MAX_RETRIES,
+                        "Maximale transiente Retries muss mindestens 1 sein (aktuell: " + value + "). "
+                        + "Der Wert 0 ist unzulässig."));
+            }
+        } catch (NumberFormatException e) {
+            findings.add(EditorValidationFinding.error(FIELD_MAX_RETRIES,
+                    "Maximale transiente Retries muss eine ganze Zahl >= 1 sein."));
+        }
+    }
+
+    private void validateMaxPages(String rawValue, List<EditorValidationFinding> findings) {
+        if (rawValue.isBlank()) {
+            findings.add(EditorValidationFinding.error(FIELD_MAX_PAGES,
+                    "Maximale Seitenzahl darf nicht leer sein."));
+            return;
+        }
+        try {
+            int value = Integer.parseInt(rawValue.strip());
+            if (value <= 0) {
+                findings.add(EditorValidationFinding.error(FIELD_MAX_PAGES,
+                        "Maximale Seitenzahl muss positiv sein (aktuell: " + value + ")."));
+            } else if (value > MAX_PAGES_HINT_THRESHOLD) {
+                findings.add(EditorValidationFinding.hint(FIELD_MAX_PAGES,
+                        "Plausibilitätshinweis: Über " + MAX_PAGES_HINT_THRESHOLD
+                        + " Seiten je Datei könnten die Verarbeitung verlangsamen (aktuell: " + value + ")."));
+            }
+        } catch (NumberFormatException e) {
+            findings.add(EditorValidationFinding.error(FIELD_MAX_PAGES,
+                    "Maximale Seitenzahl muss eine positive ganze Zahl sein."));
+        }
+    }
+
+    private void validateMaxTextCharacters(String rawValue, List<EditorValidationFinding> findings) {
+        if (rawValue.isBlank()) {
+            findings.add(EditorValidationFinding.error(FIELD_MAX_CHARS,
+                    "Maximale Zeichenzahl darf nicht leer sein."));
+            return;
+        }
+        try {
+            int value = Integer.parseInt(rawValue.strip());
+            if (value <= 0) {
+                findings.add(EditorValidationFinding.error(FIELD_MAX_CHARS,
+                        "Maximale Zeichenzahl muss positiv sein (aktuell: " + value + ")."));
+            } else if (value > MAX_CHARS_STRONG_WARNING_THRESHOLD) {
+                findings.add(EditorValidationFinding.warning(FIELD_MAX_CHARS,
+                        "Stark erhöhte Zeichenmenge: " + value + " Zeichen können zu riskant hohen "
+                        + "API-Kosten je Verarbeitungsaufruf führen."));
+            } else if (value > MAX_CHARS_WARNING_THRESHOLD) {
+                findings.add(EditorValidationFinding.warning(FIELD_MAX_CHARS,
+                        "Erhöhte Zeichenmenge: " + value + " Zeichen. Beachten Sie mögliche Auswirkungen "
+                        + "auf die API-Kosten je Verarbeitungsaufruf."));
+            }
+            // 1–1000: unkritisch, kein Befund
+        } catch (NumberFormatException e) {
+            findings.add(EditorValidationFinding.error(FIELD_MAX_CHARS,
+                    "Maximale Zeichenzahl muss eine positive ganze Zahl sein."));
+        }
+    }
+
+    // =========================================================================
+    // Aktiver Provider – providerabhängige Felder
+    // =========================================================================
+
+    private void validateActiveProviderFields(EditorValidationInput input,
+                                              List<EditorValidationFinding> findings) {
+        Optional<AiProviderFamily> resolvedProvider =
+                AiProviderFamily.fromIdentifier(input.activeProviderIdentifier());
+        if (resolvedProvider.isEmpty()) {
+            // Provider unbekannt – feldspezifische Provider-Prüfungen nicht möglich
+            return;
+        }
+
+        AiProviderFamily family = resolvedProvider.get();
+        switch (family) {
+            case CLAUDE -> validateClaudeFields(input, findings);
+            case OPENAI_COMPATIBLE -> validateOpenAiFields(input, findings);
+        }
+    }
+
+    private void validateClaudeFields(EditorValidationInput input,
+                                      List<EditorValidationFinding> findings) {
+        // Basis-URL: leer ist Warnung (Default-URL wird verwendet)
+        if (input.claudeBaseUrl().isBlank()) {
+            findings.add(EditorValidationFinding.warning(FIELD_CLAUDE_BASE_URL,
+                    "Basis-URL nicht gesetzt – es wird die Standard-URL verwendet."));
+        }
+
+        // Modell: Pflichtfeld
+        if (input.claudeModel().isBlank()) {
+            findings.add(EditorValidationFinding.error(FIELD_CLAUDE_MODEL,
+                    "Modellname darf nicht leer sein."));
+        }
+
+        // Timeout
+        validateTimeoutField(input.claudeTimeoutSeconds(), FIELD_CLAUDE_TIMEOUT, findings);
+
+        // API-Key
+        validateApiKeyFindings(input.claudeApiKeyDescriptor(), FIELD_CLAUDE_API_KEY, findings);
+    }
+
+    private void validateOpenAiFields(EditorValidationInput input,
+                                      List<EditorValidationFinding> findings) {
+        // Basis-URL: leer ist Warnung
+        if (input.openaiBaseUrl().isBlank()) {
+            findings.add(EditorValidationFinding.warning(FIELD_OPENAI_BASE_URL,
+                    "Basis-URL nicht gesetzt – es wird die Standard-URL verwendet."));
+        }
+
+        // Modell: Pflichtfeld
+        if (input.openaiModel().isBlank()) {
+            findings.add(EditorValidationFinding.error(FIELD_OPENAI_MODEL,
+                    "Modellname darf nicht leer sein."));
+        }
+
+        // Timeout
+        validateTimeoutField(input.openaiTimeoutSeconds(), FIELD_OPENAI_TIMEOUT, findings);
+
+        // API-Key
+        validateApiKeyFindings(input.openaiApiKeyDescriptor(), FIELD_OPENAI_API_KEY, findings);
+    }
+
+    private void validateTimeoutField(String rawValue, String fieldKey,
+                                      List<EditorValidationFinding> findings) {
+        if (rawValue.isBlank()) {
+            findings.add(EditorValidationFinding.error(fieldKey,
+                    "Timeout-Wert darf nicht leer sein."));
+            return;
+        }
+        try {
+            int value = Integer.parseInt(rawValue.strip());
+            if (value <= 0) {
+                findings.add(EditorValidationFinding.error(fieldKey,
+                        "Timeout-Wert muss positiv sein (aktuell: " + value + ")."));
+            }
+        } catch (NumberFormatException e) {
+            findings.add(EditorValidationFinding.error(fieldKey,
+                    "Timeout-Wert muss eine positive ganze Zahl sein."));
+        }
+    }
+
+    /**
+     * Erzeugt API-Key-Befunde gemäß der Vorrangregel.
+     * <p>
+     * Vorrangregel:
+     * <ol>
+     *   <li>ENV-Variable aktiv: INFO-Befund mit Variablenname</li>
+     *   <li>Property-Wert in Datei, keine ENV: normal (kein Befund)</li>
+     *   <li>Leeres Property-Feld und keine ENV: WARNING</li>
+     * </ol>
+     *
+     * @param descriptor  Herkunft des effektiven API-Schlüssels
+     * @param fieldKey    Property-Schlüssel des API-Key-Felds
+     * @param findings    Zielliste für neue Befunde
+     */
+    private void validateApiKeyFindings(EffectiveApiKeyDescriptor descriptor,
+                                        String fieldKey,
+                                        List<EditorValidationFinding> findings) {
+        ApiKeyOrigin origin = descriptor.origin();
+
+        switch (origin) {
+            case FROM_PROVIDER_ENV_VAR -> {
+                String varName = descriptor.envVarName().orElse("unbekannte ENV-Variable");
+                findings.add(EditorValidationFinding.info(fieldKey,
+                        "API-Schlüssel stammt aus Umgebungsvariable " + varName
+                        + " (hat Vorrang vor dem Datei-Wert)."));
+            }
+            case FROM_LEGACY_ENV_VAR -> {
+                String varName = descriptor.envVarName().orElse("unbekannte Legacy-ENV-Variable");
+                findings.add(EditorValidationFinding.info(fieldKey,
+                        "API-Schlüssel stammt aus Legacy-Umgebungsvariable " + varName
+                        + " (hat Vorrang vor dem Datei-Wert)."));
+            }
+            case FROM_PROPERTY_FILE -> {
+                // Property-Wert vorhanden, kein ENV-Override: alles in Ordnung, kein Befund
+            }
+            case ABSENT -> {
+                findings.add(EditorValidationFinding.warning(fieldKey,
+                        "Kein API-Schlüssel hinterlegt. Ohne Schlüssel kann der Provider "
+                        + "nicht genutzt werden."));
+            }
+        }
+    }
+}
diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationFinding.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationFinding.java
new file mode 100644
index 0000000..303765e
--- /dev/null
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationFinding.java
@@ -0,0 +1,108 @@
+package de.gecheckt.pdf.umbenenner.application.validation.editor;
+
+import java.util.Objects;
+import java.util.Optional;
+
+/**
+ * Ein einzelner Validierungsbefund für den aktuellen Editorzustand.
+ * <p>
+ * Ein Befund beschreibt eine erkannte Auffälligkeit in der Konfiguration mit einem
+ * Schweregrad, einem Feldbezug und einer deutschen Beschreibung. Das {@code fieldKey}-Feld
+ * verwendet denselben Property-Schlüssel wie die {@code .properties}-Datei
+ * (z. B. {@code "source.folder"} oder {@code "ai.provider.openai-compatible.apiKey"}).
+ * <p>
+ * Ein Befund kann entweder feld-spezifisch sein (mit gesetztem {@code fieldKey}) oder
+ * allgemein (mit leerem {@code fieldKey}), wenn er sich nicht auf ein einzelnes Feld bezieht.
+ * <p>
+ * Befunde sind immutable und enthalten keine JavaFX-Typen.
+ *
+ * @param fieldKey  optionaler Property-Schlüssel des betroffenen Felds; leer wenn feld-unabhängig
+ * @param severity  Schweregrad des Befunds; nie {@code null}
+ * @param message   deutschsprachige Beschreibung; nie {@code null}
+ */
+public record EditorValidationFinding(
+        Optional<String> fieldKey,
+        EditorValidationSeverity severity,
+        String message) {
+
+    /**
+     * Erstellt einen neuen Validierungsbefund.
+     *
+     * @param fieldKey  optionaler Property-Schlüssel; {@code null} wird zu {@link Optional#empty()}
+     * @param severity  Schweregrad; darf nicht {@code null} sein
+     * @param message   deutschsprachige Beschreibung; darf nicht {@code null} sein
+     * @throws NullPointerException wenn {@code severity} oder {@code message} {@code null} sind
+     */
+    public EditorValidationFinding {
+        Objects.requireNonNull(severity, "severity must not be null");
+        Objects.requireNonNull(message, "message must not be null");
+        fieldKey = fieldKey == null ? Optional.empty() : fieldKey;
+    }
+
+    /**
+     * Erstellt einen feldbezogenen Fehler-Befund.
+     *
+     * @param fieldKey  Property-Schlüssel des betroffenen Felds; darf nicht {@code null} sein
+     * @param message   deutschsprachige Fehlerbeschreibung; darf nicht {@code null} sein
+     * @return ein neuer Befund mit Schweregrad {@link EditorValidationSeverity#ERROR}
+     */
+    public static EditorValidationFinding error(String fieldKey, String message) {
+        Objects.requireNonNull(fieldKey, "fieldKey must not be null");
+        return new EditorValidationFinding(Optional.of(fieldKey), EditorValidationSeverity.ERROR, message);
+    }
+
+    /**
+     * Erstellt einen feldbezogenen Warn-Befund.
+     *
+     * @param fieldKey  Property-Schlüssel des betroffenen Felds; darf nicht {@code null} sein
+     * @param message   deutschsprachige Warnbeschreibung; darf nicht {@code null} sein
+     * @return ein neuer Befund mit Schweregrad {@link EditorValidationSeverity#WARNING}
+     */
+    public static EditorValidationFinding warning(String fieldKey, String message) {
+        Objects.requireNonNull(fieldKey, "fieldKey must not be null");
+        return new EditorValidationFinding(Optional.of(fieldKey), EditorValidationSeverity.WARNING, message);
+    }
+
+    /**
+     * Erstellt einen feldbezogenen Hinweis-Befund.
+     *
+     * @param fieldKey  Property-Schlüssel des betroffenen Felds; darf nicht {@code null} sein
+     * @param message   deutschsprachige Hinweisbeschreibung; darf nicht {@code null} sein
+     * @return ein neuer Befund mit Schweregrad {@link EditorValidationSeverity#HINT}
+     */
+    public static EditorValidationFinding hint(String fieldKey, String message) {
+        Objects.requireNonNull(fieldKey, "fieldKey must not be null");
+        return new EditorValidationFinding(Optional.of(fieldKey), EditorValidationSeverity.HINT, message);
+    }
+
+    /**
+     * Erstellt einen allgemeinen Informationsbefund ohne Feldbezug.
+     *
+     * @param message  deutschsprachige Informationsbeschreibung; darf nicht {@code null} sein
+     * @return ein neuer Befund mit Schweregrad {@link EditorValidationSeverity#INFO}
+     */
+    public static EditorValidationFinding info(String message) {
+        return new EditorValidationFinding(Optional.empty(), EditorValidationSeverity.INFO, message);
+    }
+
+    /**
+     * Erstellt einen feldbezogenen Informationsbefund.
+     *
+     * @param fieldKey  Property-Schlüssel des betroffenen Felds; darf nicht {@code null} sein
+     * @param message   deutschsprachige Informationsbeschreibung; darf nicht {@code null} sein
+     * @return ein neuer Befund mit Schweregrad {@link EditorValidationSeverity#INFO}
+     */
+    public static EditorValidationFinding info(String fieldKey, String message) {
+        Objects.requireNonNull(fieldKey, "fieldKey must not be null");
+        return new EditorValidationFinding(Optional.of(fieldKey), EditorValidationSeverity.INFO, message);
+    }
+
+    /**
+     * Gibt an, ob dieser Befund feld-spezifisch ist.
+     *
+     * @return {@code true} wenn ein {@code fieldKey} gesetzt ist
+     */
+    public boolean hasFieldKey() {
+        return fieldKey.isPresent();
+    }
+}
diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationInput.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationInput.java
new file mode 100644
index 0000000..a11a6d8
--- /dev/null
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationInput.java
@@ -0,0 +1,99 @@
+package de.gecheckt.pdf.umbenenner.application.validation.editor;
+
+import java.util.Objects;
+
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor;
+
+/**
+ * Eingabedaten für den {@link EditorConfigurationValidator}.
+ * <p>
+ * Enthält den gesamten aktuellen Editorzustand als String-Werte, so wie sie im Editor
+ * vorliegen – ohne Parsing, Typumwandlung oder Existenzprüfungen. Der Validator bewertet
+ * ausschließlich diese Werte.
+ * <p>
+ * Pfad-Existenzprüfungen und Roundtrips (SQLite, Prompt-Datei, Netzwerk) sind explizit
+ * ausgeschlossen und gehören in spätere technische Gesamtprüfungen.
+ * <p>
+ * Dieser Record enthält keine JavaFX-Typen und keine Infrastrukturabhängigkeiten.
+ *
+ * @param activeProviderIdentifier  Rohtextwert von {@code ai.provider.active}
+ * @param sourceFolder              Rohtextwert von {@code source.folder}
+ * @param targetFolder              Rohtextwert von {@code target.folder}
+ * @param sqliteFile                Rohtextwert von {@code sqlite.file}
+ * @param promptTemplateFile        Rohtextwert von {@code prompt.template.file}
+ * @param maxRetriesTransient       Rohtextwert von {@code max.retries.transient}
+ * @param maxPages                  Rohtextwert von {@code max.pages}
+ * @param maxTextCharacters         Rohtextwert von {@code max.text.characters}
+ * @param claudeBaseUrl             Rohtextwert der Claude-Basis-URL
+ * @param claudeModel               Rohtextwert des Claude-Modellnamens
+ * @param claudeTimeoutSeconds      Rohtextwert des Claude-Timeouts
+ * @param claudeApiKeyDescriptor    API-Key-Herkunft für den Claude-Provider; nie {@code null}
+ * @param openaiBaseUrl             Rohtextwert der OpenAI-kompatiblen Basis-URL
+ * @param openaiModel               Rohtextwert des OpenAI-kompatiblen Modellnamens
+ * @param openaiTimeoutSeconds      Rohtextwert des OpenAI-kompatiblen Timeouts
+ * @param openaiApiKeyDescriptor    API-Key-Herkunft für den OpenAI-kompatiblen Provider; nie {@code null}
+ */
+public record EditorValidationInput(
+        String activeProviderIdentifier,
+        String sourceFolder,
+        String targetFolder,
+        String sqliteFile,
+        String promptTemplateFile,
+        String maxRetriesTransient,
+        String maxPages,
+        String maxTextCharacters,
+        String claudeBaseUrl,
+        String claudeModel,
+        String claudeTimeoutSeconds,
+        EffectiveApiKeyDescriptor claudeApiKeyDescriptor,
+        String openaiBaseUrl,
+        String openaiModel,
+        String openaiTimeoutSeconds,
+        EffectiveApiKeyDescriptor openaiApiKeyDescriptor) {
+
+    /**
+     * Erstellt eine neue Eingabe für den Validator.
+     *
+     * @param activeProviderIdentifier  aktiver Provider-Bezeichner; {@code null} wird zu leerem String
+     * @param sourceFolder              Quellordner-Pfad; {@code null} wird zu leerem String
+     * @param targetFolder              Zielordner-Pfad; {@code null} wird zu leerem String
+     * @param sqliteFile                SQLite-Dateipfad; {@code null} wird zu leerem String
+     * @param promptTemplateFile        Prompt-Dateipfad; {@code null} wird zu leerem String
+     * @param maxRetriesTransient       max. transiente Retries; {@code null} wird zu leerem String
+     * @param maxPages                  max. Seitenzahl; {@code null} wird zu leerem String
+     * @param maxTextCharacters         max. Zeichenzahl; {@code null} wird zu leerem String
+     * @param claudeBaseUrl             Claude-Basis-URL; {@code null} wird zu leerem String
+     * @param claudeModel               Claude-Modellname; {@code null} wird zu leerem String
+     * @param claudeTimeoutSeconds      Claude-Timeout; {@code null} wird zu leerem String
+     * @param claudeApiKeyDescriptor    Claude-API-Key-Herkunft; darf nicht {@code null} sein
+     * @param openaiBaseUrl             OpenAI-Basis-URL; {@code null} wird zu leerem String
+     * @param openaiModel               OpenAI-Modellname; {@code null} wird zu leerem String
+     * @param openaiTimeoutSeconds      OpenAI-Timeout; {@code null} wird zu leerem String
+     * @param openaiApiKeyDescriptor    OpenAI-API-Key-Herkunft; darf nicht {@code null} sein
+     * @throws NullPointerException wenn {@code claudeApiKeyDescriptor} oder {@code openaiApiKeyDescriptor} {@code null} sind
+     */
+    public EditorValidationInput {
+        activeProviderIdentifier = normalizeText(activeProviderIdentifier);
+        sourceFolder = normalizeText(sourceFolder);
+        targetFolder = normalizeText(targetFolder);
+        sqliteFile = normalizeText(sqliteFile);
+        promptTemplateFile = normalizeText(promptTemplateFile);
+        maxRetriesTransient = normalizeText(maxRetriesTransient);
+        maxPages = normalizeText(maxPages);
+        maxTextCharacters = normalizeText(maxTextCharacters);
+        claudeBaseUrl = normalizeText(claudeBaseUrl);
+        claudeModel = normalizeText(claudeModel);
+        claudeTimeoutSeconds = normalizeText(claudeTimeoutSeconds);
+        claudeApiKeyDescriptor = Objects.requireNonNull(claudeApiKeyDescriptor,
+                "claudeApiKeyDescriptor must not be null");
+        openaiBaseUrl = normalizeText(openaiBaseUrl);
+        openaiModel = normalizeText(openaiModel);
+        openaiTimeoutSeconds = normalizeText(openaiTimeoutSeconds);
+        openaiApiKeyDescriptor = Objects.requireNonNull(openaiApiKeyDescriptor,
+                "openaiApiKeyDescriptor must not be null");
+    }
+
+    private static String normalizeText(String value) {
+        return value == null ? "" : value;
+    }
+}
diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationReport.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationReport.java
new file mode 100644
index 0000000..9a2dd2d
--- /dev/null
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationReport.java
@@ -0,0 +1,63 @@
+package de.gecheckt.pdf.umbenenner.application.validation.editor;
+
+import java.util.List;
+import java.util.Objects;
+
+/**
+ * Ergebnis einer editornahen Konfigurationsvalidierung.
+ * <p>
+ * Enthält alle Befunde, die der {@link EditorConfigurationValidator} aus dem aktuellen
+ * Editorzustand abgeleitet hat. Das Ergebnis ist immutable.
+ * <p>
+ * Befunde können über {@link #findings()} als vollständige Liste abgerufen werden.
+ * Feldbezogene Befunde lassen sich über {@link EditorValidationFinding#hasFieldKey()} filtern.
+ *
+ * @param findings  alle Validierungsbefunde; nie {@code null}
+ */
+public record EditorValidationReport(List<EditorValidationFinding> findings) {
+
+    /**
+     * Erstellt ein Validierungsergebnis.
+     *
+     * @param findings  Befundliste; darf nicht {@code null} sein
+     * @throws NullPointerException wenn {@code findings} {@code null} ist
+     */
+    public EditorValidationReport {
+        Objects.requireNonNull(findings, "findings must not be null");
+        findings = List.copyOf(findings);
+    }
+
+    /**
+     * Erstellt ein leeres Ergebnis ohne Befunde.
+     *
+     * @return ein leeres Ergebnis; nie {@code null}
+     */
+    public static EditorValidationReport empty() {
+        return new EditorValidationReport(List.of());
+    }
+
+    /**
+     * Gibt an, ob mindestens ein Befund mit Schweregrad {@link EditorValidationSeverity#ERROR} vorhanden ist.
+     * <p>
+     * Wenn {@code true}, gilt die Konfiguration als nicht lauffähig. Das Speichern ist jedoch
+     * trotzdem erlaubt.
+     *
+     * @return {@code true} wenn mindestens ein Fehler-Befund vorliegt
+     */
+    public boolean hasErrors() {
+        return findings.stream().anyMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    /**
+     * Gibt alle Befunde zurück, die sich auf das angegebene Feld beziehen.
+     *
+     * @param fieldKey  Property-Schlüssel des gesuchten Felds; darf nicht {@code null} sein
+     * @return unveränderliche Liste der feldbezogenen Befunde; nie {@code null}
+     */
+    public List<EditorValidationFinding> findingsFor(String fieldKey) {
+        Objects.requireNonNull(fieldKey, "fieldKey must not be null");
+        return findings.stream()
+                .filter(f -> f.fieldKey().isPresent() && f.fieldKey().get().equals(fieldKey))
+                .toList();
+    }
+}
diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationSeverity.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationSeverity.java
new file mode 100644
index 0000000..6331921
--- /dev/null
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorValidationSeverity.java
@@ -0,0 +1,30 @@
+package de.gecheckt.pdf.umbenenner.application.validation.editor;
+
+/**
+ * Schweregrade für Befunde der editornahen Konfigurationsvalidierung.
+ * <p>
+ * Die Reihenfolge entspricht aufsteigender Kritikalität:
+ * <ol>
+ *   <li>{@link #INFO} – neutraler Informationshinweis, keine Handlung erforderlich</li>
+ *   <li>{@link #HINT} – nützlicher Hinweis, den der Benutzer berücksichtigen sollte</li>
+ *   <li>{@link #WARNING} – riskante, aber formal zulässige Einstellung</li>
+ *   <li>{@link #ERROR} – ungültige oder fehlende Pflichtangabe, Konfiguration nicht lauffähig</li>
+ * </ol>
+ * <p>
+ * Warnungen und Hinweise verhindern das Speichern nicht. Fehler markieren den Stand als
+ * nicht lauffähig, erlauben aber ebenfalls das Speichern.
+ */
+public enum EditorValidationSeverity {
+
+    /** Neutraler Informationshinweis. */
+    INFO,
+
+    /** Nützlicher Hinweis, den der Benutzer beachten sollte. */
+    HINT,
+
+    /** Riskante, aber formal zulässige Einstellung. */
+    WARNING,
+
+    /** Ungültige oder fehlende Pflichtangabe – Konfiguration ist nicht lauffähig. */
+    ERROR
+}
diff --git a/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/package-info.java b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/package-info.java
new file mode 100644
index 0000000..e0dce6f
--- /dev/null
+++ b/pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/validation/editor/package-info.java
@@ -0,0 +1,16 @@
+/**
+ * Editornahe Validierungskomponenten für den Konfigurationseditor.
+ * <p>
+ * Dieses Package enthält den zentralen {@link de.gecheckt.pdf.umbenenner.application.validation.editor.EditorConfigurationValidator},
+ * der den aktuellen Editorzustand gegen fachliche und technische Regeln prüft und
+ * Befunde der Stufen Fehler, Warnung, Hinweis und Info erzeugt.
+ * <p>
+ * Die Komponenten sind infrastrukturneutral: Sie kennen keine JavaFX-Typen, keine
+ * Dateisystempfade, keine Datenbankzugriffe und keine HTTP-Kommunikation. Alle Prüfungen
+ * arbeiten ausschließlich auf den übergebenen String-Werten des aktuellen Editorzustands.
+ * <p>
+ * Die Ergebnistypen ({@link de.gecheckt.pdf.umbenenner.application.validation.editor.EditorValidationFinding}
+ * und {@link de.gecheckt.pdf.umbenenner.application.validation.editor.EditorValidationReport}) sind immutable
+ * Records und enthalten keine Infrastrukturabhängigkeiten.
+ */
+package de.gecheckt.pdf.umbenenner.application.validation.editor;
diff --git a/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ApiKeyOriginTest.java b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ApiKeyOriginTest.java
new file mode 100644
index 0000000..d7ae654
--- /dev/null
+++ b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ApiKeyOriginTest.java
@@ -0,0 +1,28 @@
+package de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link ApiKeyOrigin}.
+ */
+class ApiKeyOriginTest {
+
+    @Test
+    void allValuesPresent() {
+        assertThat(ApiKeyOrigin.values()).containsExactlyInAnyOrder(
+                ApiKeyOrigin.FROM_PROVIDER_ENV_VAR,
+                ApiKeyOrigin.FROM_LEGACY_ENV_VAR,
+                ApiKeyOrigin.FROM_PROPERTY_FILE,
+                ApiKeyOrigin.ABSENT);
+    }
+
+    @Test
+    void enumLookupByName() {
+        assertThat(ApiKeyOrigin.valueOf("FROM_PROVIDER_ENV_VAR")).isEqualTo(ApiKeyOrigin.FROM_PROVIDER_ENV_VAR);
+        assertThat(ApiKeyOrigin.valueOf("FROM_LEGACY_ENV_VAR")).isEqualTo(ApiKeyOrigin.FROM_LEGACY_ENV_VAR);
+        assertThat(ApiKeyOrigin.valueOf("FROM_PROPERTY_FILE")).isEqualTo(ApiKeyOrigin.FROM_PROPERTY_FILE);
+        assertThat(ApiKeyOrigin.valueOf("ABSENT")).isEqualTo(ApiKeyOrigin.ABSENT);
+    }
+}
diff --git a/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/EffectiveApiKeyDescriptorTest.java b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/EffectiveApiKeyDescriptorTest.java
new file mode 100644
index 0000000..58a80f0
--- /dev/null
+++ b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/EffectiveApiKeyDescriptorTest.java
@@ -0,0 +1,88 @@
+package de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Optional;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatNullPointerException;
+
+/**
+ * Tests for {@link EffectiveApiKeyDescriptor}.
+ */
+class EffectiveApiKeyDescriptorTest {
+
+    @Test
+    void fromProviderEnvVar_setsOriginAndVarName() {
+        var descriptor = EffectiveApiKeyDescriptor.fromProviderEnvVar("ANTHROPIC_API_KEY");
+
+        assertThat(descriptor.origin()).isEqualTo(ApiKeyOrigin.FROM_PROVIDER_ENV_VAR);
+        assertThat(descriptor.envVarName()).contains("ANTHROPIC_API_KEY");
+        assertThat(descriptor.isFromEnvironmentVariable()).isTrue();
+        assertThat(descriptor.isAbsent()).isFalse();
+    }
+
+    @Test
+    void fromLegacyEnvVar_setsOriginAndVarName() {
+        var descriptor = EffectiveApiKeyDescriptor.fromLegacyEnvVar("OPENAI_API_KEY");
+
+        assertThat(descriptor.origin()).isEqualTo(ApiKeyOrigin.FROM_LEGACY_ENV_VAR);
+        assertThat(descriptor.envVarName()).contains("OPENAI_API_KEY");
+        assertThat(descriptor.isFromEnvironmentVariable()).isTrue();
+        assertThat(descriptor.isAbsent()).isFalse();
+    }
+
+    @Test
+    void fromPropertyFile_setsOriginAndEmptyVarName() {
+        var descriptor = EffectiveApiKeyDescriptor.fromPropertyFile();
+
+        assertThat(descriptor.origin()).isEqualTo(ApiKeyOrigin.FROM_PROPERTY_FILE);
+        assertThat(descriptor.envVarName()).isEmpty();
+        assertThat(descriptor.isFromEnvironmentVariable()).isFalse();
+        assertThat(descriptor.isAbsent()).isFalse();
+    }
+
+    @Test
+    void absent_setsAbsentOriginAndEmptyVarName() {
+        var descriptor = EffectiveApiKeyDescriptor.absent();
+
+        assertThat(descriptor.origin()).isEqualTo(ApiKeyOrigin.ABSENT);
+        assertThat(descriptor.envVarName()).isEmpty();
+        assertThat(descriptor.isFromEnvironmentVariable()).isFalse();
+        assertThat(descriptor.isAbsent()).isTrue();
+    }
+
+    @Test
+    void nullEnvVarNameBecomesEmpty() {
+        var descriptor = new EffectiveApiKeyDescriptor(ApiKeyOrigin.FROM_PROPERTY_FILE, null);
+        assertThat(descriptor.envVarName()).isEqualTo(Optional.empty());
+    }
+
+    @Test
+    void rejectsNullOrigin() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new EffectiveApiKeyDescriptor(null, Optional.empty()));
+    }
+
+    @Test
+    void fromProviderEnvVar_rejectsNullName() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> EffectiveApiKeyDescriptor.fromProviderEnvVar(null));
+    }
+
+    @Test
+    void fromLegacyEnvVar_rejectsNullName() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> EffectiveApiKeyDescriptor.fromLegacyEnvVar(null));
+    }
+
+    @Test
+    void equality_basedOnAllFields() {
+        var a = EffectiveApiKeyDescriptor.fromProviderEnvVar("VAR_A");
+        var b = EffectiveApiKeyDescriptor.fromProviderEnvVar("VAR_A");
+        var c = EffectiveApiKeyDescriptor.fromProviderEnvVar("VAR_B");
+
+        assertThat(a).isEqualTo(b);
+        assertThat(a).isNotEqualTo(c);
+    }
+}
diff --git a/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogRequestTest.java b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogRequestTest.java
new file mode 100644
index 0000000..bd7a09a
--- /dev/null
+++ b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogRequestTest.java
@@ -0,0 +1,59 @@
+package de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Optional;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+import static org.assertj.core.api.Assertions.assertThatNullPointerException;
+
+/**
+ * Tests for {@link ModelCatalogRequest}.
+ */
+class ModelCatalogRequestTest {
+
+    @Test
+    void storesAllProvidedValues() {
+        var request = new ModelCatalogRequest(
+                "claude",
+                Optional.of("https://api.anthropic.com"),
+                Optional.of("test-key"),
+                30);
+
+        assertThat(request.providerIdentifier()).isEqualTo("claude");
+        assertThat(request.baseUrl()).contains("https://api.anthropic.com");
+        assertThat(request.apiKey()).contains("test-key");
+        assertThat(request.timeoutSeconds()).isEqualTo(30);
+    }
+
+    @Test
+    void nullBaseUrlBecomesEmpty() {
+        var request = new ModelCatalogRequest("claude", null, Optional.of("key"), 10);
+        assertThat(request.baseUrl()).isEmpty();
+    }
+
+    @Test
+    void nullApiKeyBecomesEmpty() {
+        var request = new ModelCatalogRequest("claude", Optional.empty(), null, 10);
+        assertThat(request.apiKey()).isEmpty();
+    }
+
+    @Test
+    void rejectsNullProviderIdentifier() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new ModelCatalogRequest(null, Optional.empty(), Optional.empty(), 10));
+    }
+
+    @Test
+    void rejectsZeroTimeout() {
+        assertThatIllegalArgumentException()
+                .isThrownBy(() -> new ModelCatalogRequest("claude", Optional.empty(), Optional.empty(), 0));
+    }
+
+    @Test
+    void rejectsNegativeTimeout() {
+        assertThatIllegalArgumentException()
+                .isThrownBy(() -> new ModelCatalogRequest("claude", Optional.empty(), Optional.empty(), -5));
+    }
+}
diff --git a/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogResultTest.java b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogResultTest.java
new file mode 100644
index 0000000..fe81f7c
--- /dev/null
+++ b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/port/out/modelcatalog/ModelCatalogResultTest.java
@@ -0,0 +1,159 @@
+package de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog;
+
+import org.junit.jupiter.api.Test;
+
+import java.time.Instant;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatNullPointerException;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+
+/**
+ * Tests for {@link ModelCatalogResult} and its permitted sub-types.
+ */
+class ModelCatalogResultTest {
+
+    // ── Success ─────────────────────────────────────────────────────────────
+
+    @Test
+    void success_storesAllFields() {
+        var now = Instant.now();
+        var result = new ModelCatalogResult.Success("claude", List.of("claude-3-5-sonnet", "claude-3-opus"), now);
+
+        assertThat(result.providerIdentifier()).isEqualTo("claude");
+        assertThat(result.models()).containsExactly("claude-3-5-sonnet", "claude-3-opus");
+        assertThat(result.loadedAt()).isEqualTo(now);
+    }
+
+    @Test
+    void success_modelListIsDefensiveCopy() {
+        var mutable = new java.util.ArrayList<>(List.of("model-a"));
+        var result = new ModelCatalogResult.Success("claude", mutable, Instant.now());
+        mutable.add("model-b");
+
+        assertThat(result.models()).containsExactly("model-a");
+    }
+
+    @Test
+    void success_rejectsNullProviderIdentifier() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new ModelCatalogResult.Success(null, List.of("m"), Instant.now()));
+    }
+
+    @Test
+    void success_rejectsNullModelList() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new ModelCatalogResult.Success("claude", null, Instant.now()));
+    }
+
+    @Test
+    void success_rejectsEmptyModelList() {
+        assertThatIllegalArgumentException()
+                .isThrownBy(() -> new ModelCatalogResult.Success("claude", List.of(), Instant.now()));
+    }
+
+    @Test
+    void success_rejectsNullTimestamp() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new ModelCatalogResult.Success("claude", List.of("m"), null));
+    }
+
+    // ── EmptyList ────────────────────────────────────────────────────────────
+
+    @Test
+    void emptyList_storesAllFields() {
+        var now = Instant.now();
+        var result = new ModelCatalogResult.EmptyList("openai-compatible", now);
+
+        assertThat(result.providerIdentifier()).isEqualTo("openai-compatible");
+        assertThat(result.loadedAt()).isEqualTo(now);
+    }
+
+    @Test
+    void emptyList_rejectsNullProviderIdentifier() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new ModelCatalogResult.EmptyList(null, Instant.now()));
+    }
+
+    @Test
+    void emptyList_rejectsNullTimestamp() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new ModelCatalogResult.EmptyList("claude", null));
+    }
+
+    // ── IncompleteConfiguration ──────────────────────────────────────────────
+
+    @Test
+    void incompleteConfiguration_storesAllFields() {
+        var result = new ModelCatalogResult.IncompleteConfiguration("claude", "API-Schluessel fehlt");
+
+        assertThat(result.providerIdentifier()).isEqualTo("claude");
+        assertThat(result.missingReason()).isEqualTo("API-Schluessel fehlt");
+    }
+
+    @Test
+    void incompleteConfiguration_rejectsNullProviderIdentifier() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new ModelCatalogResult.IncompleteConfiguration(null, "reason"));
+    }
+
+    @Test
+    void incompleteConfiguration_rejectsNullMissingReason() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new ModelCatalogResult.IncompleteConfiguration("claude", null));
+    }
+
+    // ── TechnicalFailure ─────────────────────────────────────────────────────
+
+    @Test
+    void technicalFailure_storesAllFields() {
+        var result = new ModelCatalogResult.TechnicalFailure("openai-compatible", "HTTP_ERROR", "503 Service Unavailable");
+
+        assertThat(result.providerIdentifier()).isEqualTo("openai-compatible");
+        assertThat(result.errorCategory()).isEqualTo("HTTP_ERROR");
+        assertThat(result.errorDetail()).isEqualTo("503 Service Unavailable");
+    }
+
+    @Test
+    void technicalFailure_rejectsNullProviderIdentifier() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new ModelCatalogResult.TechnicalFailure(null, "cat", "detail"));
+    }
+
+    @Test
+    void technicalFailure_rejectsNullErrorCategory() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new ModelCatalogResult.TechnicalFailure("claude", null, "detail"));
+    }
+
+    @Test
+    void technicalFailure_rejectsNullErrorDetail() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new ModelCatalogResult.TechnicalFailure("claude", "cat", null));
+    }
+
+    // ── Pattern-matching exhaustiveness ──────────────────────────────────────
+
+    @Test
+    void patternMatchingSwitchCoversAllPermittedSubtypes() {
+        ModelCatalogResult success = new ModelCatalogResult.Success("claude", List.of("m"), Instant.now());
+        ModelCatalogResult empty = new ModelCatalogResult.EmptyList("claude", Instant.now());
+        ModelCatalogResult incomplete = new ModelCatalogResult.IncompleteConfiguration("claude", "reason");
+        ModelCatalogResult failure = new ModelCatalogResult.TechnicalFailure("claude", "TIMEOUT", "detail");
+
+        assertThat(classifyResult(success)).isEqualTo("success");
+        assertThat(classifyResult(empty)).isEqualTo("empty");
+        assertThat(classifyResult(incomplete)).isEqualTo("incomplete");
+        assertThat(classifyResult(failure)).isEqualTo("failure");
+    }
+
+    private String classifyResult(ModelCatalogResult result) {
+        return switch (result) {
+            case ModelCatalogResult.Success s -> "success";
+            case ModelCatalogResult.EmptyList e -> "empty";
+            case ModelCatalogResult.IncompleteConfiguration i -> "incomplete";
+            case ModelCatalogResult.TechnicalFailure t -> "failure";
+        };
+    }
+}
diff --git a/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorConfigurationValidatorTest.java b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorConfigurationValidatorTest.java
new file mode 100644
index 0000000..6225321
--- /dev/null
+++ b/pdf-umbenenner-application/src/test/java/de/gecheckt/pdf/umbenenner/application/validation/editor/EditorConfigurationValidatorTest.java
@@ -0,0 +1,512 @@
+package de.gecheckt.pdf.umbenenner.application.validation.editor;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.List;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.EffectiveApiKeyDescriptor;
+
+/**
+ * Unit-Tests für den {@link EditorConfigurationValidator}.
+ * <p>
+ * Prüft alle Validierungsregeln auf Basis synthetischer Eingaben ohne I/O.
+ */
+class EditorConfigurationValidatorTest {
+
+    private EditorConfigurationValidator validator;
+
+    @BeforeEach
+    void setUp() {
+        validator = new EditorConfigurationValidator();
+    }
+
+    // =========================================================================
+    // Hilfsmethode: minimale gültige Eingabe
+    // =========================================================================
+
+    private static EditorValidationInput minimalValidInput() {
+        return new EditorValidationInput(
+                "claude",                    // activeProviderIdentifier
+                "C:/source",                 // sourceFolder
+                "C:/target",                 // targetFolder
+                "C:/db.sqlite",              // sqliteFile
+                "C:/prompt.txt",             // promptTemplateFile
+                "3",                         // maxRetriesTransient
+                "10",                        // maxPages
+                "500",                       // maxTextCharacters
+                "https://api.anthropic.com", // claudeBaseUrl
+                "claude-3-5-sonnet",         // claudeModel
+                "30",                        // claudeTimeoutSeconds
+                EffectiveApiKeyDescriptor.fromPropertyFile(), // claudeApiKeyDescriptor
+                "https://api.openai.com",    // openaiBaseUrl
+                "gpt-4",                     // openaiModel
+                "30",                        // openaiTimeoutSeconds
+                EffectiveApiKeyDescriptor.fromPropertyFile() // openaiApiKeyDescriptor
+        );
+    }
+
+    // =========================================================================
+    // Leere Eingabe / Null-Checks
+    // =========================================================================
+
+    @Test
+    void validate_emptyActiveProvider_producesError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "500",
+                "", "", "30", EffectiveApiKeyDescriptor.absent(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.hasErrors()).isTrue();
+        assertThat(report.findings()).anyMatch(f ->
+                f.fieldKey().isPresent()
+                && f.fieldKey().get().equals(EditorConfigurationValidator.FIELD_ACTIVE_PROVIDER)
+                && f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    @Test
+    void validate_unknownActiveProvider_producesError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "unknown-provider", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "500",
+                "", "", "30", EffectiveApiKeyDescriptor.absent(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.hasErrors()).isTrue();
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_ACTIVE_PROVIDER))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    // =========================================================================
+    // Pflichtpfade
+    // =========================================================================
+
+    @Test
+    void validate_emptySourceFolder_producesError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_SOURCE_FOLDER))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    @Test
+    void validate_emptyTargetFolder_producesError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_TARGET_FOLDER))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    @Test
+    void validate_emptySqliteFile_producesError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "", "C:/prompt.txt",
+                "3", "10", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_SQLITE_FILE))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    @Test
+    void validate_emptyPromptFile_producesError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "",
+                "3", "10", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_PROMPT_FILE))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    // =========================================================================
+    // max.retries.transient
+    // =========================================================================
+
+    @Test
+    void validate_maxRetriesTransient_zero_producesError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "0", "10", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_MAX_RETRIES))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    @Test
+    void validate_maxRetriesTransient_negative_producesError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "-1", "10", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_MAX_RETRIES))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    @Test
+    void validate_maxRetriesTransient_one_producesNoError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "1", "10", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        List<EditorValidationFinding> retryFindings =
+                report.findingsFor(EditorConfigurationValidator.FIELD_MAX_RETRIES);
+        assertThat(retryFindings).noneMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    @Test
+    void validate_maxRetriesTransient_nonNumeric_producesError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "abc", "10", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_MAX_RETRIES))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    // =========================================================================
+    // max.pages
+    // =========================================================================
+
+    @Test
+    void validate_maxPages_zero_producesError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "0", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_MAX_PAGES))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    @Test
+    void validate_maxPages_over100_producesHint() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "101", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_MAX_PAGES))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.HINT);
+    }
+
+    @Test
+    void validate_maxPages_exactly100_producesNoHintAndNoError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "100", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        List<EditorValidationFinding> pageFindings =
+                report.findingsFor(EditorConfigurationValidator.FIELD_MAX_PAGES);
+        assertThat(pageFindings).noneMatch(f ->
+                f.severity() == EditorValidationSeverity.ERROR
+                || f.severity() == EditorValidationSeverity.HINT);
+    }
+
+    // =========================================================================
+    // max.text.characters – Wirtschaftliche Warnlogik
+    // =========================================================================
+
+    @Test
+    void validate_maxTextCharacters_1000_producesNoFinding() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "1000",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_MAX_CHARS))
+                .isEmpty();
+    }
+
+    @Test
+    void validate_maxTextCharacters_1001_producesWarning() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "1001",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_MAX_CHARS))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.WARNING);
+    }
+
+    @Test
+    void validate_maxTextCharacters_3000_producesWarning() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "3000",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_MAX_CHARS))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.WARNING);
+    }
+
+    @Test
+    void validate_maxTextCharacters_3001_producesStrongWarning() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "3001",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        List<EditorValidationFinding> charFindings =
+                report.findingsFor(EditorConfigurationValidator.FIELD_MAX_CHARS);
+        assertThat(charFindings).anyMatch(f -> f.severity() == EditorValidationSeverity.WARNING);
+        // Starke Warnung enthält "stark" oder "riskant"
+        assertThat(charFindings).anyMatch(f ->
+                f.message().toLowerCase().contains("stark")
+                || f.message().toLowerCase().contains("riskant"));
+    }
+
+    @Test
+    void validate_maxTextCharacters_zero_producesError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "0",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_MAX_CHARS))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    // =========================================================================
+    // Provider-Felder: Claude
+    // =========================================================================
+
+    @Test
+    void validate_claude_emptyModel_producesError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "500",
+                "https://api.anthropic.com", "", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_CLAUDE_MODEL))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    @Test
+    void validate_claude_emptyBaseUrl_producesWarning() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "500",
+                "", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_CLAUDE_BASE_URL))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.WARNING);
+    }
+
+    @Test
+    void validate_claude_negativeTimeout_producesError() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "-5",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_CLAUDE_TIMEOUT))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+
+    // =========================================================================
+    // API-Key-Vorrangregel
+    // =========================================================================
+
+    @Test
+    void validate_claude_absent_apiKey_producesWarning() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.absent(),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_CLAUDE_API_KEY))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.WARNING);
+    }
+
+    @Test
+    void validate_claude_fromPropertyFile_producesNoFinding() {
+        EditorValidationInput input = minimalValidInput();
+        // minimalValidInput() already uses fromPropertyFile() for Claude
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_CLAUDE_API_KEY))
+                .isEmpty();
+    }
+
+    @Test
+    void validate_claude_fromEnvVar_producesInfoFinding() {
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromProviderEnvVar("ANTHROPIC_API_KEY"),
+                "", "", "30", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_CLAUDE_API_KEY))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.INFO
+                        && f.message().contains("ANTHROPIC_API_KEY"));
+    }
+
+    @Test
+    void validate_openai_fromLegacyEnvVar_producesInfoFinding() {
+        EditorValidationInput input = new EditorValidationInput(
+                "openai-compatible", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "500",
+                "", "", "30", EffectiveApiKeyDescriptor.absent(),
+                "https://api.openai.com", "gpt-4", "30",
+                EffectiveApiKeyDescriptor.fromLegacyEnvVar("PDF_UMBENENNER_API_KEY"));
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_OPENAI_API_KEY))
+                .anyMatch(f -> f.severity() == EditorValidationSeverity.INFO
+                        && f.message().contains("PDF_UMBENENNER_API_KEY"));
+    }
+
+    // =========================================================================
+    // Vollständig gültige Konfiguration
+    // =========================================================================
+
+    @Test
+    void validate_fullyValidClaudeConfig_producesNoErrors() {
+        EditorValidationInput input = minimalValidInput();
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.hasErrors()).isFalse();
+    }
+
+    @Test
+    void validate_fullyValidOpenAiConfig_producesNoErrors() {
+        EditorValidationInput input = new EditorValidationInput(
+                "openai-compatible", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "500",
+                "", "", "30", EffectiveApiKeyDescriptor.absent(),
+                "https://api.openai.com", "gpt-4", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile());
+
+        EditorValidationReport report = validator.validate(input);
+
+        assertThat(report.hasErrors()).isFalse();
+    }
+
+    // =========================================================================
+    // Inaktiver Provider – keine Fehler für inaktiven Block
+    // =========================================================================
+
+    @Test
+    void validate_claude_active_openaiBlockEmpty_producesNoOpenaiErrors() {
+        // Claude ist aktiv; OpenAI-Felder sind leer – darf keinen FEHLER für OpenAI-Felder geben
+        EditorValidationInput input = new EditorValidationInput(
+                "claude", "C:/source", "C:/target", "C:/db.sqlite", "C:/prompt.txt",
+                "3", "10", "500",
+                "https://api.anthropic.com", "claude-3-5-sonnet", "30",
+                EffectiveApiKeyDescriptor.fromPropertyFile(),
+                "", "", "", EffectiveApiKeyDescriptor.absent());
+
+        EditorValidationReport report = validator.validate(input);
+
+        // OpenAI-Felder dürfen keinen Fehler produzieren (Provider nicht aktiv)
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_OPENAI_MODEL))
+                .noneMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+        assertThat(report.findingsFor(EditorConfigurationValidator.FIELD_OPENAI_TIMEOUT))
+                .noneMatch(f -> f.severity() == EditorValidationSeverity.ERROR);
+    }
+}
diff --git a/pdf-umbenenner-bootstrap/src/main/java/de/gecheckt/pdf/umbenenner/bootstrap/BootstrapRunner.java b/pdf-umbenenner-bootstrap/src/main/java/de/gecheckt/pdf/umbenenner/bootstrap/BootstrapRunner.java
index b2be5c2..d47bde8 100644
--- a/pdf-umbenenner-bootstrap/src/main/java/de/gecheckt/pdf/umbenenner/bootstrap/BootstrapRunner.java
+++ b/pdf-umbenenner-bootstrap/src/main/java/de/gecheckt/pdf/umbenenner/bootstrap/BootstrapRunner.java
@@ -20,7 +20,11 @@ import de.gecheckt.pdf.umbenenner.adapter.in.gui.GuiConfigurationFileLoader;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.GuiConfigurationFileWriter;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.GuiConfigurationLoadException;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.GuiStartupContext;
+import de.gecheckt.pdf.umbenenner.bootstrap.adapter.AiModelCatalogDispatcher;
 import de.gecheckt.pdf.umbenenner.bootstrap.adapter.GuiConfigurationPropertiesWriter;
+import de.gecheckt.pdf.umbenenner.adapter.out.modelcatalog.ClaudeModelCatalogAdapter;
+import de.gecheckt.pdf.umbenenner.adapter.out.modelcatalog.OpenAiCompatibleModelCatalogAdapter;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.AiModelCatalogPort;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationEditorState;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationEditorStateFactory;
 import de.gecheckt.pdf.umbenenner.adapter.in.gui.editor.GuiConfigurationFileSnapshot;
@@ -616,13 +620,18 @@ public class BootstrapRunner {
     private GuiStartupContext buildGuiStartupContext(Optional<String> configPathOverride) {
         GuiConfigurationFileLoader loader = this::loadGuiConfigurationState;
         GuiConfigurationFileWriter writer = new GuiConfigurationPropertiesWriter();
+        AiModelCatalogPort modelCatalogPort = buildModelCatalogDispatcher();
+        de.gecheckt.pdf.umbenenner.application.validation.editor.ApiKeyResolutionPort apiKeyResolutionPort =
+                new de.gecheckt.pdf.umbenenner.adapter.out.validation.EnvironmentApiKeyResolutionAdapter();
 
         if (configPathOverride.isEmpty()) {
             return new GuiStartupContext(
                     GuiConfigurationEditorStateFactory.createBlankStartState(),
                     Optional.empty(),
                     loader,
-                    writer);
+                    writer,
+                    modelCatalogPort,
+                    apiKeyResolutionPort);
         }
 
         Path configPath = Paths.get(configPathOverride.get());
@@ -634,13 +643,16 @@ public class BootstrapRunner {
                     Optional.of("Konfigurationsdatei nicht gefunden: " + configPath.toAbsolutePath()
                             + "\nDie GUI startet ohne Konfigurationsdatei."),
                     loader,
-                    writer);
+                    writer,
+                    modelCatalogPort,
+                    apiKeyResolutionPort);
         }
 
         LOG.info("GUI startup: configuration file confirmed at: {}", configPath.toAbsolutePath());
         try {
             GuiConfigurationEditorState loadedState = loadGuiConfigurationState(configPath);
-            return new GuiStartupContext(loadedState, Optional.empty(), loader, writer);
+            return new GuiStartupContext(loadedState, Optional.empty(), loader, writer,
+                    modelCatalogPort, apiKeyResolutionPort);
         } catch (GuiConfigurationLoadException e) {
             LOG.error("GUI startup: configuration could not be loaded, starting without it: {}",
                     e.getMessage(), e);
@@ -648,10 +660,29 @@ public class BootstrapRunner {
                     GuiConfigurationEditorStateFactory.createBlankStartState(),
                     Optional.of("Konfiguration konnte nicht geladen werden: " + e.getMessage()),
                     loader,
-                    writer);
+                    writer,
+                    modelCatalogPort,
+                    apiKeyResolutionPort);
         }
     }
 
+    /**
+     * Creates the {@link AiModelCatalogPort} dispatcher for use in the GUI startup context.
+     * <p>
+     * Instantiates one stateless concrete adapter per supported provider family and wires
+     * them into an {@link AiModelCatalogDispatcher}. The adapters are stateless: all
+     * provider-specific values (API key, base URL, timeout) are supplied per call via the
+     * {@link de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogRequest},
+     * so no provider configuration needs to be resolved at this point.
+     *
+     * @return a ready-to-use model catalogue port; never {@code null}
+     */
+    private AiModelCatalogPort buildModelCatalogDispatcher() {
+        return new AiModelCatalogDispatcher(
+                new ClaudeModelCatalogAdapter(),
+                new OpenAiCompatibleModelCatalogAdapter());
+    }
+
     private GuiConfigurationEditorState loadGuiConfigurationState(Path configFilePath) {
         try {
             boolean legacyDetected = detectedLegacyConfiguration(configFilePath);
diff --git a/pdf-umbenenner-bootstrap/src/main/java/de/gecheckt/pdf/umbenenner/bootstrap/adapter/AiModelCatalogDispatcher.java b/pdf-umbenenner-bootstrap/src/main/java/de/gecheckt/pdf/umbenenner/bootstrap/adapter/AiModelCatalogDispatcher.java
new file mode 100644
index 0000000..09490ae
--- /dev/null
+++ b/pdf-umbenenner-bootstrap/src/main/java/de/gecheckt/pdf/umbenenner/bootstrap/adapter/AiModelCatalogDispatcher.java
@@ -0,0 +1,91 @@
+package de.gecheckt.pdf.umbenenner.bootstrap.adapter;
+
+import java.util.Objects;
+
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.AiModelCatalogPort;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogRequest;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult;
+
+/**
+ * Composition-root dispatcher that routes {@link AiModelCatalogPort#fetchAvailableModels}
+ * calls to the concrete adapter matching the provider identifier carried in the request.
+ * <p>
+ * This class is not a new architectural layer between the port contract and its adapters.
+ * It is a Bootstrap-only wiring convenience that allows the GUI to call a single
+ * {@link AiModelCatalogPort} instance regardless of which provider the user has currently
+ * selected. The concrete adapters remain independent of each other and of this class.
+ * <p>
+ * <strong>Dispatching rule:</strong> The value of
+ * {@link ModelCatalogRequest#providerIdentifier()} is matched case-sensitively against
+ * the known provider identifiers:
+ * <ul>
+ *   <li>{@code "claude"} — routed to the Claude adapter</li>
+ *   <li>{@code "openai-compatible"} — routed to the OpenAI-compatible adapter</li>
+ *   <li>any other value — returns {@link ModelCatalogResult.IncompleteConfiguration}
+ *       with a human-readable explanation</li>
+ * </ul>
+ * <p>
+ * <strong>Thread safety:</strong> The dispatcher holds only immutable references to
+ * the two concrete adapters and is trivially thread-safe.
+ */
+public class AiModelCatalogDispatcher implements AiModelCatalogPort {
+
+    private static final Logger LOG = LogManager.getLogger(AiModelCatalogDispatcher.class);
+
+    private static final String PROVIDER_CLAUDE = "claude";
+    private static final String PROVIDER_OPENAI_COMPATIBLE = "openai-compatible";
+
+    private final AiModelCatalogPort claudeAdapter;
+    private final AiModelCatalogPort openAiCompatibleAdapter;
+
+    /**
+     * Creates a dispatcher wired with both supported adapter implementations.
+     *
+     * @param claudeAdapter              the adapter for the Claude provider family;
+     *                                   must not be {@code null}
+     * @param openAiCompatibleAdapter    the adapter for the OpenAI-compatible provider family;
+     *                                   must not be {@code null}
+     * @throws NullPointerException if either adapter is {@code null}
+     */
+    public AiModelCatalogDispatcher(AiModelCatalogPort claudeAdapter,
+                                    AiModelCatalogPort openAiCompatibleAdapter) {
+        this.claudeAdapter = Objects.requireNonNull(claudeAdapter,
+                "claudeAdapter must not be null");
+        this.openAiCompatibleAdapter = Objects.requireNonNull(openAiCompatibleAdapter,
+                "openAiCompatibleAdapter must not be null");
+    }
+
+    /**
+     * Routes the model catalogue request to the concrete adapter for the provider
+     * identified by {@link ModelCatalogRequest#providerIdentifier()}.
+     * <p>
+     * If the provider identifier does not match any known provider, returns
+     * {@link ModelCatalogResult.IncompleteConfiguration} without calling any adapter.
+     * This keeps the GUI informed without any crash or exception.
+     *
+     * @param request all values needed to contact the provider; must not be {@code null}
+     * @return the result from the matched adapter, or {@link ModelCatalogResult.IncompleteConfiguration}
+     *         when the provider identifier is unknown; never {@code null}
+     * @throws NullPointerException if {@code request} is {@code null}
+     */
+    @Override
+    public ModelCatalogResult fetchAvailableModels(ModelCatalogRequest request) {
+        Objects.requireNonNull(request, "request must not be null");
+
+        String provider = request.providerIdentifier();
+        LOG.debug("Model catalogue dispatch: routing request for provider '{}'", provider);
+
+        return switch (provider) {
+            case PROVIDER_CLAUDE -> claudeAdapter.fetchAvailableModels(request);
+            case PROVIDER_OPENAI_COMPATIBLE -> openAiCompatibleAdapter.fetchAvailableModels(request);
+            default -> {
+                LOG.warn("Model catalogue dispatch: unknown provider identifier '{}'", provider);
+                yield new ModelCatalogResult.IncompleteConfiguration(provider,
+                        "Unbekannter Provider: '" + provider + "'");
+            }
+        };
+    }
+}
diff --git a/pdf-umbenenner-bootstrap/src/test/java/de/gecheckt/pdf/umbenenner/bootstrap/adapter/AiModelCatalogDispatcherTest.java b/pdf-umbenenner-bootstrap/src/test/java/de/gecheckt/pdf/umbenenner/bootstrap/adapter/AiModelCatalogDispatcherTest.java
new file mode 100644
index 0000000..0febc36
--- /dev/null
+++ b/pdf-umbenenner-bootstrap/src/test/java/de/gecheckt/pdf/umbenenner/bootstrap/adapter/AiModelCatalogDispatcherTest.java
@@ -0,0 +1,145 @@
+package de.gecheckt.pdf.umbenenner.bootstrap.adapter;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatNullPointerException;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoInteractions;
+import static org.mockito.Mockito.when;
+
+import java.time.Instant;
+import java.util.List;
+import java.util.Optional;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.AiModelCatalogPort;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogRequest;
+import de.gecheckt.pdf.umbenenner.application.port.out.modelcatalog.ModelCatalogResult;
+
+/**
+ * Unit tests for {@link AiModelCatalogDispatcher}.
+ * <p>
+ * Verifies that the dispatcher correctly routes requests to the matching concrete
+ * adapter based on the provider identifier in the request, and that unknown providers
+ * are handled as {@link ModelCatalogResult.IncompleteConfiguration} without calling
+ * either adapter.
+ */
+@ExtendWith(MockitoExtension.class)
+class AiModelCatalogDispatcherTest {
+
+    @Mock
+    private AiModelCatalogPort claudeAdapter;
+
+    @Mock
+    private AiModelCatalogPort openAiCompatibleAdapter;
+
+    private AiModelCatalogDispatcher dispatcher;
+
+    @BeforeEach
+    void setUp() {
+        dispatcher = new AiModelCatalogDispatcher(claudeAdapter, openAiCompatibleAdapter);
+    }
+
+    @Test
+    @DisplayName("Request with provider 'claude' is routed to the Claude adapter")
+    void dispatch_claudeProvider_routesToClaudeAdapter() {
+        ModelCatalogRequest request = new ModelCatalogRequest(
+                "claude", Optional.empty(), Optional.of("key"), 5);
+        ModelCatalogResult expected = new ModelCatalogResult.Success(
+                "claude", List.of("claude-3-opus"), Instant.now());
+        when(claudeAdapter.fetchAvailableModels(request)).thenReturn(expected);
+
+        ModelCatalogResult result = dispatcher.fetchAvailableModels(request);
+
+        assertThat(result).isSameAs(expected);
+        verify(claudeAdapter).fetchAvailableModels(request);
+        verifyNoInteractions(openAiCompatibleAdapter);
+    }
+
+    @Test
+    @DisplayName("Request with provider 'openai-compatible' is routed to the OpenAI-compatible adapter")
+    void dispatch_openAiCompatibleProvider_routesToOpenAiAdapter() {
+        ModelCatalogRequest request = new ModelCatalogRequest(
+                "openai-compatible", Optional.empty(), Optional.of("key"), 5);
+        ModelCatalogResult expected = new ModelCatalogResult.Success(
+                "openai-compatible", List.of("gpt-4o"), Instant.now());
+        when(openAiCompatibleAdapter.fetchAvailableModels(request)).thenReturn(expected);
+
+        ModelCatalogResult result = dispatcher.fetchAvailableModels(request);
+
+        assertThat(result).isSameAs(expected);
+        verify(openAiCompatibleAdapter).fetchAvailableModels(request);
+        verifyNoInteractions(claudeAdapter);
+    }
+
+    @Test
+    @DisplayName("Unknown provider identifier returns IncompleteConfiguration without calling any adapter")
+    void dispatch_unknownProvider_returnsIncompleteConfigurationWithoutCallingAdapters() {
+        ModelCatalogRequest request = new ModelCatalogRequest(
+                "unknown-provider", Optional.empty(), Optional.of("key"), 5);
+
+        ModelCatalogResult result = dispatcher.fetchAvailableModels(request);
+
+        assertThat(result).isInstanceOf(ModelCatalogResult.IncompleteConfiguration.class);
+        ModelCatalogResult.IncompleteConfiguration incomplete =
+                (ModelCatalogResult.IncompleteConfiguration) result;
+        assertThat(incomplete.providerIdentifier()).isEqualTo("unknown-provider");
+        assertThat(incomplete.missingReason()).containsIgnoringCase("Unbekannter Provider");
+        verifyNoInteractions(claudeAdapter);
+        verifyNoInteractions(openAiCompatibleAdapter);
+    }
+
+    @Test
+    @DisplayName("Null request throws NullPointerException")
+    void dispatch_nullRequest_throwsNullPointerException() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> dispatcher.fetchAvailableModels(null));
+    }
+
+    @Test
+    @DisplayName("Null Claude adapter throws NullPointerException at construction")
+    void constructor_nullClaudeAdapter_throwsNullPointerException() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new AiModelCatalogDispatcher(null, openAiCompatibleAdapter));
+    }
+
+    @Test
+    @DisplayName("Null OpenAI-compatible adapter throws NullPointerException at construction")
+    void constructor_nullOpenAiAdapter_throwsNullPointerException() {
+        assertThatNullPointerException()
+                .isThrownBy(() -> new AiModelCatalogDispatcher(claudeAdapter, null));
+    }
+
+    @Test
+    @DisplayName("Dispatcher propagates adapter result unchanged for claude")
+    void dispatch_claudeAdapter_propagatesResultUnchanged() {
+        ModelCatalogRequest request = new ModelCatalogRequest(
+                "claude", Optional.empty(), Optional.of("k"), 10);
+        ModelCatalogResult.TechnicalFailure failure = new ModelCatalogResult.TechnicalFailure(
+                "claude", "AUTHENTICATION_FAILED", "Bad credentials");
+        when(claudeAdapter.fetchAvailableModels(request)).thenReturn(failure);
+
+        ModelCatalogResult result = dispatcher.fetchAvailableModels(request);
+
+        assertThat(result).isSameAs(failure);
+    }
+
+    @Test
+    @DisplayName("Dispatcher propagates adapter result unchanged for openai-compatible")
+    void dispatch_openAiCompatibleAdapter_propagatesResultUnchanged() {
+        ModelCatalogRequest request = new ModelCatalogRequest(
+                "openai-compatible", Optional.empty(), Optional.of("k"), 10);
+        ModelCatalogResult.EmptyList emptyList = new ModelCatalogResult.EmptyList(
+                "openai-compatible", Instant.now());
+        when(openAiCompatibleAdapter.fetchAvailableModels(request)).thenReturn(emptyList);
+
+        ModelCatalogResult result = dispatcher.fetchAvailableModels(request);
+
+        assertThat(result).isSameAs(emptyList);
+    }
+}