feat(events): align message events with checkpoint format and add middleware tag injection

- Message events (ai_message, ai_tool_call, tool_result, human_message) now use
  BaseMessage.model_dump() format, matching LangGraph checkpoint values.messages
- on_tool_end extracts tool_call_id/name/status from ToolMessage objects
- on_tool_error now emits tool_result message events with error status
- record_middleware uses middleware:{tag} event_type and middleware category
- Summarization custom events use middleware:summarize category
- TitleMiddleware injects middleware:title tag via get_config() inheritance
- SummarizationMiddleware model bound with middleware:summarize tag
- Worker writes human_message using HumanMessage.model_dump()

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

backend/packages/harness/deerflow/agents/lead_agent/agent.py

@@ -56,13 +56,15 @@ def _create_summarization_middleware() -> SummarizationMiddleware | None:
     # Prepare keep parameter
     keep = config.keep.to_tuple()
 
-    # Prepare model parameter
+    # Prepare model parameter.
+    # Bind "middleware:summarize" tag so RunJournal identifies these LLM calls
+    # as middleware rather than lead_agent (SummarizationMiddleware is a
+    # LangChain built-in, so we tag the model at creation time).
     if config.model_name:
         model = create_chat_model(name=config.model_name, thinking_enabled=False)
     else:
-        # Use a lightweight model for summarization to save costs
-        # Falls back to default model if not explicitly specified
         model = create_chat_model(thinking_enabled=False)
+    model = model.with_config(tags=["middleware:summarize"])
 
     # Prepare kwargs
     kwargs = {