fix(events): use metadata flag instead of heuristic for dict content detection

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/packages/harness/deerflow/runtime/events/store/db.py

@@ -30,10 +30,10 @@ class DbRunEventStore(RunEventStore):
             d["created_at"] = val.isoformat()
         d.pop("id", None)
         # Restore dict content that was JSON-serialized on write
-        content = d.get("content", "")
+        raw = d.get("content", "")
-        if isinstance(content, str) and content and content[0] in ("{", "["):
+        if isinstance(raw, str) and d.get("metadata", {}).get("content_is_dict"):
             try:
-                d["content"] = json.loads(content)
+                d["content"] = json.loads(raw)
             except (json.JSONDecodeError, ValueError):
                 pass
         return d
@@ -48,7 +48,11 @@ class DbRunEventStore(RunEventStore):
 
     async def put(self, *, thread_id, run_id, event_type, category, content="", metadata=None, created_at=None):
         content, metadata = self._truncate_trace(category, content, metadata)
-        db_content = json.dumps(content, default=str, ensure_ascii=False) if isinstance(content, dict) else content
+        if isinstance(content, dict):
+            db_content = json.dumps(content, default=str, ensure_ascii=False)
+            metadata = {**(metadata or {}), "content_is_dict": True}
+        else:
+            db_content = content
         async with self._sf() as session:
             max_seq = await session.scalar(select(func.max(RunEventRow.seq)).where(RunEventRow.thread_id == thread_id))
             seq = (max_seq or 0) + 1
@@ -82,7 +86,11 @@ class DbRunEventStore(RunEventStore):
                 category = e.get("category", "trace")
                 metadata = e.get("metadata")
                 content, metadata = self._truncate_trace(category, content, metadata)
-                db_content = json.dumps(content, default=str, ensure_ascii=False) if isinstance(content, dict) else content
+                if isinstance(content, dict):
+                    db_content = json.dumps(content, default=str, ensure_ascii=False)
+                    metadata = {**(metadata or {}), "content_is_dict": True}
+                else:
+                    db_content = content
                 row = RunEventRow(
                     thread_id=e["thread_id"],
                     run_id=e["run_id"],

backend/tests/test_run_journal.py

@@ -419,6 +419,58 @@ class TestDbBackedLifecycle:
         await close_engine()
 
 
+class TestDictContentFlag:
+    """Verify that content_is_dict metadata flag controls deserialization."""
+
+    @pytest.mark.anyio
+    async def test_db_store_str_starting_with_brace_not_deserialized(self, tmp_path):
+        """Plain string content starting with { should NOT be deserialized."""
+        from deerflow.persistence.engine import close_engine, get_session_factory, init_engine
+        from deerflow.runtime.events.store.db import DbRunEventStore
+
+        url = f"sqlite+aiosqlite:///{tmp_path / 'test.db'}"
+        await init_engine("sqlite", url=url, sqlite_dir=str(tmp_path))
+        sf = get_session_factory()
+        store = DbRunEventStore(sf)
+
+        record = await store.put(
+            thread_id="t1",
+            run_id="r1",
+            event_type="tool_end",
+            category="trace",
+            content="{not json, just a string}",
+        )
+        events = await store.list_events("t1", "r1")
+        assert events[0]["content"] == "{not json, just a string}"
+        assert isinstance(events[0]["content"], str)
+
+        await close_engine()
+
+    @pytest.mark.anyio
+    async def test_db_store_str_starting_with_bracket_not_deserialized(self, tmp_path):
+        """Plain string content like '[1, 2, 3]' should NOT be deserialized."""
+        from deerflow.persistence.engine import close_engine, get_session_factory, init_engine
+        from deerflow.runtime.events.store.db import DbRunEventStore
+
+        url = f"sqlite+aiosqlite:///{tmp_path / 'test.db'}"
+        await init_engine("sqlite", url=url, sqlite_dir=str(tmp_path))
+        sf = get_session_factory()
+        store = DbRunEventStore(sf)
+
+        record = await store.put(
+            thread_id="t1",
+            run_id="r1",
+            event_type="tool_end",
+            category="trace",
+            content="[1, 2, 3]",
+        )
+        events = await store.list_events("t1", "r1")
+        assert events[0]["content"] == "[1, 2, 3]"
+        assert isinstance(events[0]["content"], str)
+
+        await close_engine()
+
+
 class TestDictContent:
     """Verify that store backends accept str | dict content."""