fix: add observability log to apply_update JSON parse failure

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

memory.py

@@ -20,7 +20,8 @@ def apply_update(state: dict, raw_json: str) -> dict:
         start = raw_json.find("{")
         end = raw_json.rfind("}") + 1
         update = TurnUpdate.model_validate_json(raw_json[start:end])
-    except Exception:
+    except Exception as e:
+        print(f"[apply_update] JSON parse failed: {e!r} | raw: {raw_json[:120]!r}")
         update = TurnUpdate()
 
     state["affinity"] = max(0, min(100, state["affinity"] + update.affinity_delta))