acp: Fix close session not found error (#54009)

Follow up to #53999

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Closes #ISSUE

Release Notes:

- N/A
ff108c89d7Bennet Bo Fenner committed on 4/16/2026, 12:11:06 PM· committed by GitHubparent36557bd
4 files changedLine totals unavailable