fix(services): add SQLite error handling and strengthen top_k test

app/services/bm25_index.py

@@ -47,12 +47,18 @@ class BM25Index:
         """Rebuild from SQLite if dirty."""
         if not self._dirty:
             return
+        try:
             conn = sqlite3.connect(db_path)
             conn.row_factory = sqlite3.Row
+            try:
                 rows = conn.execute(
                     "SELECT id, doc_id, page_number, text FROM page_chunks ORDER BY doc_id, page_number"
                 ).fetchall()
+            finally:
                 conn.close()
+        except sqlite3.Error as exc:
+            logger.error("BM25 index rebuild failed: %s", exc)
+            return
         self._load_chunks([dict(r) for r in rows])
         self._dirty = False
         logger.info("BM25 index rebuilt: %d chunks", len(self._chunks))

tests/test_bm25_index.py

@@ -43,9 +43,10 @@ def test_query_returns_relevant_result():
 
 
 def test_query_respects_top_k():
+    # "action" matches all three chunks; top_k=2 must hard-cap the result list
     idx = _seeded_index()
-    results = idx.query("rules", top_k=2)
-    assert len(results) <= 2
+    results = idx.query("action", top_k=2)
+    assert len(results) == 2
 
 
 def test_query_filters_by_doc_id():