[NayukiChiba]

Modifications / 改动点

• 为 back_queue 引入关闭事件，put_back_queue 方法在写入前检查队列有效性，避免向已关闭队列入队
• WebChat 消息事件在推送响应时对 put_back_queue 返回值进行判断，队列关闭后提前终止消息链处理
• chat_service 捕获客户端断开异常，主动调用 active_event_registry 停止对应 agent，并在 finally 块中清理 back_queue
  closes [Bug] 模型思考时刷新 ChatUI，之后发的消息被卡在队列永远得不到回复 #9253, [Bug] ChatUI 模型思考时刷新页面，回复丢失 #9249

• This is NOT a breaking change. / 这不是一个破坏性变更。

Screenshots or Test Results / 运行截图或测试结果

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Checklist / 检查清单

• 😊 If there are new features added in the PR, I have discussed it with the authors through issues/emails, etc.
  / 如果 PR 中有新加入的功能，已经通过 Issue / 邮件等方式和作者讨论过。

• 👀 My changes have been well-tested, and "Verification Steps" and "Screenshots" have been provided above.
  / 我的更改经过了良好的测试，并已在上方提供了“验证步骤”和“运行截图”。

• 🤓 I have ensured that no new dependencies are introduced, OR if new dependencies are introduced, they have been added to the appropriate locations in requirements.txt and pyproject.toml.
  / 我确保没有引入新依赖库，或者引入了新依赖库的同时将其添加到 requirements.txt 和 pyproject.toml 文件相应位置。

• 😮 My changes do not introduce malicious code.
  / 我的更改没有引入恶意代码。

Summary by Sourcery

Improve WebChat SSE stream robustness by adding back-queue lifecycle control, stopping agents and clearing queues when clients disconnect, and updating message sending to avoid writing into closed response queues.

Bug Fixes:

• Prevent WebChat message sending from enqueuing responses into closed back queues after SSE disconnects.
• Ensure WebChat agents are requested to stop when clients disconnect or close streams, and clean up associated back queues.

Enhancements:

• Introduce lifecycle management for WebChat back queues with close events to coordinate senders and cleanup.
• Update WebChat streaming and message sending to use a guarded back-queue write API that respects queue closure.

Tests:

• Add tests covering WebChat back-queue lifecycle, including blocked senders and queue removal behaviour.
• Add tests verifying that WebChat chat streams request agent stop on client disconnect and stream closure.
• Adapt existing WebChat attachment tests to the new back-queue write API.

[sourcery-ai]

Hey - I've left some high level feedback:

• The new put_back_queue implementation is quite complex; consider extracting the queue-write-and-close-race logic into a small internal helper or adding inline comments to clarify why asyncio.wait with two tasks is needed and how cancellation is handled to make future maintenance easier.
• The new tests that use object.__new__(ChatService) bypass ChatService.__init__, which can make them fragile if the constructor gains required state in the future; it would be more robust to instantiate ChatService normally or provide a lightweight test-specific constructor/factory.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The new `put_back_queue` implementation is quite complex; consider extracting the queue-write-and-close-race logic into a small internal helper or adding inline comments to clarify why `asyncio.wait` with two tasks is needed and how cancellation is handled to make future maintenance easier.
- The new tests that use `object.__new__(ChatService)` bypass `ChatService.__init__`, which can make them fragile if the constructor gains required state in the future; it would be more robust to instantiate `ChatService` normally or provide a lightweight test-specific constructor/factory.

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[gemini-code-assist]

Code Review

This pull request refactors the webchat queue management system to gracefully handle client disconnections by introducing a new put_back_queue method and managing queue close events. Feedback on these changes suggests checking the return value of put_back_queue in send_streaming to stop generator iteration early, and wrapping the database persistence call flush_pending_bot_message() in asyncio.shield within the finally block to ensure pending messages are saved even if the task is cancelled.

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[gemini-code-assist]

在 send_streaming 中处理 audio_chunk 时，未对 put_back_queue 的返回值进行判断。如果客户端已断开连接且队列已关闭，我们应该停止迭代生成器并提前返回，以避免不必要的后台处理和资源浪费。

Suggested change

	await webchat_queue_mgr.put_back_queue(request_id, payload)
	accepted = await webchat_queue_mgr.put_back_queue(request_id, payload)
	if not accepted:
	return

[gemini-code-assist]

当 SSE 流任务被取消（例如由于客户端断开连接）时，在 finally 块中直接 await flush_pending_bot_message() 会立即抛出 CancelledError，从而可能导致最后一条机器人消息无法成功持久化。使用 asyncio.shield 包裹它可以确保即使在任务取消时，挂起的消息也能成功保存到数据库中。

Suggested change

	await flush_pending_bot_message()
	await asyncio.shield(flush_pending_bot_message())

[Soulter]

#9259 fixed