Content review - The output did not replace the preset_response

[zzl0924]

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Dify version

v0.8.3-fix1

Cloud or Self Hosted

Self Hosted (Source)

Steps to reproduce

When Chatflow has "Review output content" enabled and the API extension returns violations and a preset_response, the original content is not replaced with the preset response in the preview.

but only "Review input content" enabled is ok.

✔️ Expected Behavior

"Review output content" enabled support

❌ Actual Behavior

No response

[dosubot]

Hi @zzl0924! I'm Dosu and I’m helping the dify team.

This is a known issue caused by a race condition in Dify's output moderation pipeline. There are existing bug reports tracking this: #29033 and #29334.

Why input moderation works but output doesn't:

• Input moderation uses exception-based control flow — it directly raises a ModerationError exception with the preset_response, which guarantees immediate delivery
• Output moderation uses event-based flow — it publishes a QueueMessageReplaceEvent, but the queue listener is stopped immediately after QueueMessageEndEvent, so the replacement event is never processed

As of now, no fix has been merged. The suggested solution involves adding synchronization to delay queue termination until moderation threads complete.

To reply, just mention @dosu.

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