dify - 💡(How to fix) Fix Phoenix tracing is lost after resuming HITL workflows [1 pull requests]

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Dify version

main branch, observed on commit c7d30bf09a after Phoenix workflow tracing support.

Cloud or Self Hosted

Self Hosted (Source)

Steps to reproduce

1. Configure the Arize/Phoenix tracing provider for a workflow or advanced-chat app.
2. Create a workflow that contains a Human Input / HITL node and can complete successfully after the submitted form resumes execution.
3. Run the workflow until it pauses at the HITL node.
4. Submit the HITL form so the workflow resumes and reaches a terminal state.
5. Check Phoenix traces and backend logs.

Observed log context includes:

Human Input node suspended workflow for form
Task resume_app_execution ... received
Unhandled event type: NodeRunHumanInputFormFilledEvent
Task resume_app_execution ... succeeded

✔️ Expected Behavior

After a paused HITL workflow or advanced-chat flow resumes and later succeeds, fails, or stops, Dify should enqueue the existing terminal workflow trace task so Phoenix receives the final workflow trace.

Pause itself does not need to emit a checkpoint trace.

❌ Actual Behavior

Phoenix receives no workflow trace for the resumed execution.

The resumed generate entity is loaded from persisted pause state, but trace_manager is excluded from serialization. After resume, terminal workflow events still reach the persistence layer, but _enqueue_trace_task() returns early because there is no TraceQueueManager.