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.

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

Begin at the /chat entry point and reproduce on Windows 10 with app version 1.0.64-1 while sending a chat turn and follow-up. Trace the turn lifecycle and its visible status handling; done means an in-flight turn has a clear working/streaming state and stalls or errors are surfaced instead of silently appearing hung.

索引モデルが issue の本文から書いたものです。