Konsolidiere Titelzeichen-Validierung in TitleCharacterRule

Doppelte private isAllowedTitleCharacters-Methoden in AiResponseValidator
und TargetFilenameBuildingService werden durch eine kanonische
TitleCharacterRule.isAllowed()-Methode ersetzt. Beide Services delegieren
jetzt dorthin statt eigene Kopien zu pflegen.

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

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/service/AiResponseValidator.java

@@ -100,7 +100,7 @@ public final class AiResponseValidator {
                     AiErrorClassification.FUNCTIONAL);
         }
 
-        if (!isAllowedTitleCharacters(title)) {
+        if (!TitleCharacterRule.isAllowed(title)) {
             return AiValidationResult.invalid(
                     "Title contains disallowed characters (only letters, digits, spaces, and hyphens are permitted): '"
                             + title + "'",
@@ -137,25 +137,6 @@ public final class AiResponseValidator {
         return AiValidationResult.valid(proposal);
     }
 
-    // -------------------------------------------------------------------------
-    // Helpers
-    // -------------------------------------------------------------------------
-
-    /**
-     * Returns {@code true} if every character in the title is a letter, digit, space, or hyphen.
-     * <p>
-     * Permits Unicode letters including German Umlauts (ä, ö, ü, Ä, Ö, Ü) and ß.
-     */
-    private static boolean isAllowedTitleCharacters(String title) {
-        for (int i = 0; i < title.length(); i++) {
-            char c = title.charAt(i);
-            if (!Character.isLetter(c) && !Character.isDigit(c) && c != ' ' && c != '-') {
-                return false;
-            }
-        }
-        return true;
-    }
-
     /**
      * Returns {@code true} if the title is a known generic placeholder.
      * Comparison is case-insensitive.

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/service/TargetFilenameBuildingService.java

@@ -149,7 +149,7 @@ public final class TargetFilenameBuildingService {
         }
 
         // After cleaning, verify that only letters, digits, spaces, and hyphens remain
-        if (!isAllowedTitleCharacters(cleanedTitle)) {
+        if (!TitleCharacterRule.isAllowed(cleanedTitle)) {
             return new InconsistentProposalState(
                     "After Windows-compatibility cleaning, title contains disallowed characters "
                             + "(only letters, digits, spaces, and hyphens are permitted): '"
@@ -165,20 +165,6 @@ public final class TargetFilenameBuildingService {
     // Helpers
     // -------------------------------------------------------------------------
 
-    /**
-     * Returns {@code true} if every character in the title is a letter, a digit, space, or hyphen.
-     * Unicode letters (including German Umlauts and ß) are permitted.
-     */
-    private static boolean isAllowedTitleCharacters(String title) {
-        for (int i = 0; i < title.length(); i++) {
-            char c = title.charAt(i);
-            if (!Character.isLetter(c) && !Character.isDigit(c) && c != ' ' && c != '-') {
-                return false;
-            }
-        }
-        return true;
-    }
-
     /**
      * Removes characters that are incompatible with Windows filenames.
      * <p>

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/service/TitleCharacterRule.java

@@ -0,0 +1,40 @@
+package de.gecheckt.pdf.umbenenner.application.service;
+
+/**
+ * Canonical rule for allowed title characters.
+ * <p>
+ * A title may contain only Unicode letters (including German Umlauts and ß),
+ * decimal digits, ASCII spaces, and hyphens ({@code -}).
+ * All other characters are considered disallowed.
+ * <p>
+ * This class is the single authoritative implementation of the character-allowlist
+ * rule. All services that need to validate or verify title characters must delegate
+ * to {@link #isAllowed(String)} instead of maintaining their own copies.
+ */
+public final class TitleCharacterRule {
+
+    private TitleCharacterRule() {
+        // utility class
+    }
+
+    /**
+     * Returns {@code true} if every character in {@code title} is a letter, digit,
+     * ASCII space, or hyphen ({@code -}).
+     * <p>
+     * Unicode letters — including German Umlauts (ä, ö, ü, Ä, Ö, Ü) and ß — are
+     * permitted. An empty string is considered allowed.
+     *
+     * @param title the title to check; must not be null
+     * @return {@code true} if all characters pass the allowlist; {@code false} otherwise
+     * @throws NullPointerException if {@code title} is null
+     */
+    public static boolean isAllowed(String title) {
+        for (int i = 0; i < title.length(); i++) {
+            char c = title.charAt(i);
+            if (!Character.isLetter(c) && !Character.isDigit(c) && c != ' ' && c != '-') {
+                return false;
+            }
+        }
+        return true;
+    }
+}

pdf-umbenenner-application/src/main/java/de/gecheckt/pdf/umbenenner/application/service/package-info.java

@@ -22,6 +22,8 @@
  *       two-level persistence</li>
  *   <li>{@link de.gecheckt.pdf.umbenenner.application.service.AiRequestComposer}
  *       — Deterministic composition of AI request representations from prompt and document text</li>
+ *   <li>{@link de.gecheckt.pdf.umbenenner.application.service.TitleCharacterRule}
+ *       — Canonical character-allowlist rule for document titles (single authoritative implementation)</li>
  * </ul>
  *
  * <h2>Document processing flow ({@code DocumentProcessingCoordinator})</h2>