App appears unresponsive (no agent reply) while window stays interactive — not frozen

**Mood:** 😞
**Category:** Bug

The Copilot app stopped responding to chat messages for an extended period (several minutes) while the window stayed fully interactive — it was **not** frozen. I could type in the composer, switch between sessions, and click UI controls, but the agent never produced a response to messages I'd sent. Follow-up messages (e.g. "are you there?") also got no reply until a restart of app, with no error, no spinner, and no "working" indicator to signal whether the turn was still in flight or had silently stalled. After restart, those messages disappeared.

**Expected:** when a turn is in flight, the app should show a clear working/streaming indicator; if the turn stalls or errors, it should surface that instead of silently appearing hung while the rest of the window stays responsive.

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| Field | Value |
| --- | --- |
| App version | 1.0.64-1 |
| OS | Windows 10.0.26200 |
| Theme | Dark |
| Path | /chat |

从 /chat 入口开始，在 Windows 10 上使用应用版本 1.0.64-1 进行复现，同时发送一个聊天轮次和后续消息。跟踪该轮次的生命周期及其可见状态处理；当进行中的轮次具有明确的工作中/流式传输状态，并且停滞或错误会被显示出来，而不是悄无声息地看起来像卡住时，即表示完成。

由索引模型根据 Issue 内容生成。