fix(web): clear responding state when annotation reply ends without workflow events

[leslie2046]

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fixes #37362

Summary

This PR fixes a UI state issue where the response may remain in the responding state after an Annotation Reply finishes.

The issue affected both:

• shared/web chat
• console debug/preview

Root Cause

In the annotation reply fast path, the SSE stream may end with message_end without ever starting a workflow.

Previously, the frontend mainly relied on workflow lifecycle events to clear the responding state, so the UI could keep showing "Stop responding" even though the response had already finished.

Fix

• treat message_end as a terminal signal when the current response never entered workflow state
• keep the existing behavior unchanged for normal workflow runs that do emit workflow events

Tests

Added targeted test coverage for:

• app/components/base/chat/chat/__tests__/hooks.spec.tsx
• app/components/workflow/panel/debug-and-preview/__tests__/hooks/sse-callbacks.spec.ts

Not run locally.

From gpt-5.5 codex

Screenshots

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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods