[Bugs] Feature Request: PR state awareness in active sessions

**Mood:** 😔
**Category:** Bugs

Feature Request: PR state awareness in active sessions

When working in a project session, the agent has no awareness of GitHub events (PR merges, reviews, comment activity) on the PR it just created — even when the merge happens from within the Copilot app itself using the merge button in the top nav. The agent only knows the PR state if the user explicitly tells it or it queries via CLI.

What I'd expect: if I merge a PR from inside the Copilot app while in the session that created it, the agent should be notified — similar to how it gets notified when a background agent completes. At minimum, the session's tracked PR status should refresh so the agent knows it's merged without me having to tell it.

Why it matters: it breaks the conversational flow — the agent is still talking about a PR being "ready for review" after I've already merged it from the same app window.

---
| Field | Value |
| --- | --- |
| App version | 1.0.10 |
| OS | macOS 26.5.1 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Week 4 |

/chat セッションフローから開始し、セッションが作成した PR をどのように追跡しているかをたどってから、top-nav の merge-button フローおよび既存の CLI ベースのステータスチェックと比較します。セッションがアプリ内からの PR のマージを反映し、エージェントがマージ済みの PR をレビュー可能として報告しなくなれば完了です。

索引モデルが issue の本文から書いたものです。