Fix #19: Fehlergrund bei fehlgeschlagenem KI-Aufruf im Begründungsbereich anzeigen

- DocumentCompletionEvent um optionales Feld failureMessage erweitert
- DocumentProcessingCoordinator leitet Fehlermeldung bei Fehler-Status durch
- GuiBatchRunResultRow um aiFailureMessage (Optional<String>) ergänzt
- GuiBatchRunCoordinator.toRow() befüllt aiFailureMessage aus dem Event
- GuiBatchRunTab.buildDetailText() zeigt bei fehlendem Reasoning und
  vorhandenem Fehlergrund: "⚠ Fehler: <Meldung>" vor dem Hinweistext
- Alle Tests angepasst und neue Unit-Tests für aiFailureMessage ergänzt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/batchrun/GuiBatchRunCoordinator.java

@@ -506,6 +506,8 @@ public final class GuiBatchRunCoordinator {
                 ? Optional.empty() : Optional.of(event.resolvedDate());
         Optional<String> reasoning = event.aiReasoning() == null || event.aiReasoning().isBlank()
                 ? Optional.empty() : Optional.of(event.aiReasoning());
+        Optional<String> failureMessage = event.failureMessage() == null || event.failureMessage().isBlank()
+                ? Optional.empty() : Optional.of(event.failureMessage());
         Duration duration = event.processingDuration();
         return new GuiBatchRunResultRow(
                 event.originalFileName(),
@@ -514,6 +516,7 @@ public final class GuiBatchRunCoordinator {
                 finalName,
                 date,
                 reasoning,
+                failureMessage,
                 duration);
     }
 

pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/batchrun/GuiBatchRunResultRow.java

@@ -34,6 +34,9 @@ import de.gecheckt.pdf.umbenenner.domain.model.DocumentFingerprint;
  *                           rename; empty otherwise
  * @param aiReasoning        the AI reasoning shown in the side panel; empty when no
  *                           reasoning is available for this row
+ * @param aiFailureMessage   eine lesbare Fehlerbeschreibung, wenn der KI-Aufruf oder die
+ *                           Verarbeitung fehlgeschlagen ist; leer bei Erfolg und
+ *                           übersprungenen Dokumenten
  * @param processingDuration wall-clock duration spent on the candidate in this run;
  *                           never {@code null} and never negative
  * @param resetPending       {@code true} when the document's persistence status has been
@@ -46,6 +49,7 @@ public record GuiBatchRunResultRow(
         Optional<String> finalFileName,
         Optional<LocalDate> resolvedDate,
         Optional<String> aiReasoning,
+        Optional<String> aiFailureMessage,
         Duration processingDuration,
         boolean resetPending) {
 
@@ -79,6 +83,7 @@ public record GuiBatchRunResultRow(
         finalFileName = finalFileName == null ? Optional.empty() : finalFileName;
         resolvedDate = resolvedDate == null ? Optional.empty() : resolvedDate;
         aiReasoning = aiReasoning == null ? Optional.empty() : aiReasoning;
+        aiFailureMessage = aiFailureMessage == null ? Optional.empty() : aiFailureMessage;
         Objects.requireNonNull(processingDuration, "processingDuration must not be null");
         if (processingDuration.isNegative()) {
             throw new IllegalArgumentException("processingDuration must not be negative");
@@ -97,6 +102,8 @@ public record GuiBatchRunResultRow(
      *                           empty)
      * @param aiReasoning        the AI reasoning text; may be {@code null} (treated as
      *                           empty)
+     * @param aiFailureMessage   eine lesbare Fehlerbeschreibung bei Fehler; may be
+     *                           {@code null} (treated as empty)
      * @param processingDuration the wall-clock processing duration; never {@code null}
      */
     public GuiBatchRunResultRow(
@@ -106,9 +113,10 @@ public record GuiBatchRunResultRow(
             Optional<String> finalFileName,
             Optional<LocalDate> resolvedDate,
             Optional<String> aiReasoning,
+            Optional<String> aiFailureMessage,
             Duration processingDuration) {
         this(originalFileName, fingerprint, status, finalFileName, resolvedDate, aiReasoning,
-                processingDuration, false);
+                aiFailureMessage, processingDuration, false);
     }
 
     /**
@@ -131,6 +139,7 @@ public record GuiBatchRunResultRow(
                 Optional.empty(),
                 Optional.empty(),
                 Optional.empty(),
+                Optional.empty(),
                 Duration.ZERO,
                 true);
     }

pdf-umbenenner-adapter-in-gui/src/main/java/de/gecheckt/pdf/umbenenner/adapter/in/gui/batchrun/GuiBatchRunTab.java

@@ -899,7 +899,11 @@ public final class GuiBatchRunTab {
         builder.append('\n');
         row.aiReasoning().ifPresentOrElse(
                 reasoning -> builder.append(reasoning),
-                () -> builder.append(NO_REASONING_TEXT));
+                () -> {
+                    row.aiFailureMessage().ifPresent(msg ->
+                            builder.append("\u26A0 Fehler: ").append(msg).append("\n\n"));
+                    builder.append(NO_REASONING_TEXT);
+                });
         return builder.toString();
     }
 
@@ -1012,6 +1016,7 @@ public final class GuiBatchRunTab {
                         Optional.empty(),
                         Optional.empty(),
                         Optional.of(message),
+                        Optional.empty(),
                         Duration.ZERO,
                         false);
                 upsertResultRowByFingerprint(missingRow);