[Bugs] Describe the bug

**Mood:** 😊
**Category:** Bugs

Describe the bug

When a new agent definition file is added to ~/.copilot/agents/ (the user-scoped agent directory), the GitHub Copilot App UI does not pick it up even after opening a new project session. A full app restart is required.

In contrast, the CLI (copilot command) correctly discovers the new agent immediately without needing a restart.

Steps to reproduce

Add a new .md agent file to ~/.copilot/agents/
Open a new project session in the App UI
Click "Default agent" dropdown — the new agent does not appear
Run copilot CLI in terminal and type /agent — the new agent appears correctly
Expected behavior

The App UI should discover user-scoped agents from ~/.copilot/agents/ when a new project session is opened, consistent with how the CLI behaves.

Actual behavior

The agent is not visible in the App UI until the entire app is quit and relaunched.

Environment

GitHub Copilot App version: 1.0.66
CLI version: 1.0.65
OS: macOS

---
| Field | Value |
| --- | --- |
| App version | 1.0.12 |
| OS | macOS 15.4.0 |
| Theme | Fox |
| Path | /chat |
| Tenure | Day 1 |

从 App UI 的新项目会话流程和“Default agent”下拉菜单开始，然后将它发现 ~/.copilot/agents/ 中文件的方式与 CLI 的 /agent 入口点进行比较。确认在打开会话前添加新的 .md agent 后，它会在无需重启应用的情况下出现，与 CLI 的行为一致。

由索引模型根据 Issue 内容生成。