feat: normalize questionData for gap-fill exercises and add placeholders if necessary

backend/services/vocabService.js

@@ -3873,6 +3873,35 @@ export default class VocabService {
 
     const plainLesson = lesson.get({ plain: true });
     const list = exercises.map((e) => e.get({ plain: true }));
+    // Normalize questionData for gap-fill hints: if text contains placeholders
+    list.forEach((ex) => {
+      try {
+        const qData = typeof ex.questionData === 'string' ? JSON.parse(ex.questionData || '{}') : (ex.questionData || {});
+        const text = String(qData.text || qData.question || '').trim();
+        const hasUnderscoreGap = /_{3,}/.test(text);
+        const hasBraceGap = /\{\s*gap\s*\}/i.test(text);
+        const hasParenPlaceholders = /\(\s*_{0,}\s*\)/.test(text);
+        // If answerData suggests a gap-like exercise and question text contains gap markers, ensure type is gap_fill
+        if ((hasUnderscoreGap || hasBraceGap || hasParenPlaceholders) && qData.type !== 'gap_fill') {
+          qData.type = 'gap_fill';
+          ex.questionData = qData;
+        }
+        // If answerData has explicit answers but there's no question text, and exerciseTypeId indicates input, add a placeholder
+        const aData = typeof ex.answerData === 'string' ? JSON.parse(ex.answerData || '{}') : (ex.answerData || {});
+        const answers = Array.isArray(aData.answers) ? aData.answers : (aData.correct ? (Array.isArray(aData.correct) ? aData.correct : [aData.correct]) : []);
+        if ((!qData.text && (!qData.question || String(qData.question).trim() === '')) && answers.length && qData.type !== 'multiple_choice') {
+          // build a minimal gap_fill text using learning hint if available in ex.title
+          const learningHintMatch = String(ex.title || '').match(/:(.*)$/);
+          const hint = learningHintMatch ? learningHintMatch[1].trim() : '';
+          qData.type = 'gap_fill';
+          qData.text = hint ? `{gap} (${hint})` : '{gap}';
+          ex.questionData = qData;
+        }
+      } catch (err) {
+        // ignore parse errors
+      }
+    });
+
     return await this._mergeSyntheticChapterLexemeMcExercises(plainLesson, list);
   }