[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 |

Start with the App UI's new project session flow and the "Default agent" dropdown, then compare how it discovers files in ~/.copilot/agents/ with the CLI's /agent entry point. Confirm that adding a new .md agent before opening a session makes it appear without restarting the app, matching the CLI behavior.

索引モデルが issue の本文から書いたものです。