flask: Context Detach Failure in Streaming Responses

[fatelei]

Describe your environment

OS: (e.g, Ubuntu)
Python version: 3.9.10
Package version: 0.48b0

What happened?

langgenius/dify#25673

2025-09-14 13:36:34.608 ERROR [Dummy-16] [__init__.py:156] - Failed to detach context
Traceback (most recent call last):
  File "/app/api/.venv/lib/python3.12/site-packages/opentelemetry/context/__init__.py", line 154, in detach
    _RUNTIME_CONTEXT.detach(token)
  File "/app/api/.venv/lib/python3.12/site-packages/opentelemetry/context/contextvars_context.py", line 50, in detach
    self._current_context.reset(token)  # type: ignore
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
RuntimeError: <Token used var=<ContextVar name='current_context' default={} at 0x7f1507563470> at 0x7f1505b11b40> has already been used once

Steps to Reproduce

1. Create an advanced chat application with a workflow in Dify
2. Run Workflow In Console
3. Check the application logs for OpenTelemetry errors

Expected Result

no error

Actual Result

raise runtime error

Additional context

No response

Would you like to implement a fix?

None

Tip

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[aabmass]

Have you seen open-telemetry/opentelemetry-python#2606? This is usually caused by a generator or async generator not being closed at the expected time, which can be fixed by adding contextlib.closing/contextlib.aclosing.

Logfire (which wraps OTel) has some great docs on this https://logfire.pydantic.dev/docs/reference/advanced/generators/