EMU migration issues in GitHub Copilot App

I have an organisation that migrated from non-EMU to EMU users.

The transition/migration from a GitHub Copilot App is quite bumpy:

- The old non-EMU user (which had the Copilot license) had to be complete remoted, so GitHub Copilot App would correctly log into the EMU organisation. The solution was to remove the non-EMU account, and the unsuccessful EMU account, and with no accounts, log in. An EMU Login with no accounts logged me in correctly into Copilot App.
- This has a side effect: The projects that were previously linked to the non-EMU account now displays the message "This project's account was Removed. Operations will use the default account. Reassign in project settings."

The only practical solution during an EMU migration is to delete all the sessions and projects, and resume. But there should a cleaner/smoother EMU migration for GitHub Clients in the App.

---
| Field | Value |
| --- | --- |
| App version | 1.1.6 |
| OS | macOS 26.5.2 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Week 14 |

尚未确定源文件、测试或入口点。首先在 macOS 上的 GitHub Copilot App 中复现从非 EMU 到 EMU 的迁移，包括已删除账户的项目状态；完成条件是定义一个迁移流程，在不删除会话和项目的情况下保留或妥善重新分配现有项目。

由索引模型根据 Issue 内容生成。