fix(cefr): resolve authentic context sentence per term and repair legacy SRS cards

- Add resolve_context_sentence_for_term to replace placeholder blanks and lookup authentic sentences from cefr_questions or books
- Fix dual mistake ingestion in process_cefr_answer to assign distinct context to target and chosen distractor
- Provide authentic context_sentence in options_breakdown and pass it via data-context in cefr.js
- Add repair_mismatched_cefr_contexts in database.py to automatically repair cards with placeholder blanks
- Bump Service Worker cache to notes-v5.9
- Add test_cefr_context_resolution_and_repair covering resolution, dual ingestion, manual add, and DB repair

app/database.py

@@ -379,6 +379,43 @@ def _migrate(conn: sqlite3.Connection):
     conn.execute("CREATE INDEX IF NOT EXISTS idx_bg_tasks_user_status ON background_tasks(user_id, status);")
     conn.execute("CREATE INDEX IF NOT EXISTS idx_bg_tasks_status ON background_tasks(status);")
 
+    # Repair legacy cards with placeholder blanks or mismatched context
+    repair_mismatched_cefr_contexts(conn)
+
+
+def repair_mismatched_cefr_contexts(conn: sqlite3.Connection):
+    """
+    Repairs legacy vocabulary cards that were imported with placeholder blanks ('___')
+    or with mismatched contexts from CEFR test questions.
+    """
+    try:
+        from app.cefr import resolve_context_sentence_for_term
+
+        # Check if table exists
+        tbl = conn.execute("SELECT 1 FROM sqlite_master WHERE type='table' AND name='vocabulary_cards'").fetchone()
+        if not tbl:
+            return
+
+        rows = conn.execute(
+            """
+            SELECT id, term, context_sentence
+            FROM vocabulary_cards
+            WHERE instr(context_sentence, '___') > 0
+            """
+        ).fetchall()
+
+        for r in rows:
+            card_id = r["id"]
+            term = r["term"]
+            old_ctx = r["context_sentence"] or ""
+            new_ctx = resolve_context_sentence_for_term(conn, term, old_ctx)
+            if new_ctx and new_ctx != old_ctx:
+                conn.execute(
+                    "UPDATE vocabulary_cards SET context_sentence = ? WHERE id = ?",
+                    (new_ctx, card_id),
+                )
+    except Exception:
+        pass
 
 
 def _seed_offline_dictionary(conn: sqlite3.Connection):