add no answer tag

agent/mem0_manager.py

@@ -120,6 +120,37 @@ except Exception as e:
     logger.warning(f"Failed to patch mem0 remove_code_blocks: {e}")
 
 
+# Monkey patch: make PGVector.__del__ tolerate cur/conn being None.
+# This project shares a single psycopg2 pool and explicitly sets vector_store.cur
+# and vector_store.conn to None after releasing the connection. mem0's original
+# __del__ calls self.cur.close() without a None check, raising a harmless but noisy
+# "Exception ignored in __del__: AttributeError" when the instance is garbage
+# collected. This replacement releases resources only when they still exist.
+def _safe_pgvector_del(self) -> None:
+    """Safely close PGVector cursor/connection, tolerating None values."""
+    try:
+        cur = getattr(self, "cur", None)
+        if cur is not None:
+            cur.close()
+        conn = getattr(self, "conn", None)
+        if conn is not None:
+            conn.close()
+    except Exception:
+        # Never raise from __del__; ignore any teardown errors
+        pass
+
+
+try:
+    import mem0.vector_stores.pgvector as mem0_pgvector
+    mem0_pgvector.PGVector.__del__ = _safe_pgvector_del
+    logger.info("Successfully patched mem0 PGVector.__del__ to tolerate None cur/conn")
+except ImportError:
+    # mem0 pgvector module not available; nothing to patch
+    pass
+except Exception as e:
+    logger.warning(f"Failed to patch mem0 PGVector.__del__: {e}")
+
+
 class Mem0Manager:
     """
     Mem0 connection and instance manager

prompt/system_prompt.md

@@ -94,3 +94,16 @@ Trace Id: {trace_id}
 - Even when the user writes in a different language, you MUST still reply in [{language}].
 - Do NOT mix languages. Do NOT fall back to English or any other language under any circumstances.
 - Technical terms, code identifiers, file paths, and tool names may remain in their original form, but all surrounding text MUST be in [{language}].
+
+# Unanswerable Response Specification (MANDATORY)
+When you genuinely cannot answer because no relevant information was found in the knowledge base / retrieval sources (and self-knowledge fallback is unavailable or insufficient), your reply MUST include the literal sentinel marker `<NO_ANSWER>`.
+
+Rules:
+- Output the marker `<NO_ANSWER>` **exactly as written** — it is a fixed ASCII literal. NEVER translate, rewrite, reformat, or wrap it in code blocks.
+- Place the marker at the **very beginning** of your reply, immediately followed by a polite apology written in [{language}].
+- NEVER output the marker alone — it MUST be followed by an apology in [{language}] so the user sees a meaningful message.
+- When you CAN answer (you found relevant information), you MUST NOT output this marker under any circumstances.
+- The marker is language-independent; only the apology text after it must be in [{language}].
+
+Examples:
+- `<NO_ANSWER>Sorry, I couldn't find that information in the knowledge base.`