This PR fixes issues with subagent cancellation, prior to this we would still show a wait indicator for subagents that were cancelled from the parent thread. We also removed the `stop_by_user` workaround, that code path now uses `thread.cancel` directly Before you mark this PR as ready for review, make sure that you have: - [x] Added a solid test coverage and/or screenshots from doing manual testing - [x] Done a self-review taking into account security and performance aspects - [x] Aligned any UI changes with the [UI checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist) Release Notes: - N/A --------- Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>