fix(uninstall): spawn windows cleanup helper via cmd start trampoline

[BlackHole1]

On Windows, oo uninstall left the running executable behind. The post-exit cleanup helper was launched with Bun.spawn({ detached: true })

• unref(), but on Windows Bun places spawned children in a kill-on-close job object and detached (UV_PROCESS_DETACHED) does not break the child out of it. The helper was killed the instant the main process exited — before it could unlink the running image — leaving oo.exe on disk.

Launch the helper through a cmd /c start "" /b trampoline instead, which creates it as a process that breaks away from the job object and outlives the parent. Await the bootstrap cmd (rather than detached + unref) so start has launched the helper before we exit, closing the race where the job could close and kill cmd before start ran. The generated self-delete script is unchanged.

Update the Windows unit assertion for the new command shape, and add a real (non-mock) win32 integration test: a child process runs performSelfUninstall, exits, and the deferred executable must then be removed by the helper — covering the real spawn path that was previously exercised only through a mock.

The job-object behavior reproduces on bun 1.3.14 and 1.4.0-canary.1 (the Rust rewrite), so this is a deliberate long-term workaround rather than a version-specific patch.

Repro: https://github.com/BlackHole1/bun-detached-windows-bug
Issue: oven-sh/bun#31603

[coderabbitai]

Summary by CodeRabbit

Release Notes

• Bug Fixes

  • Improved Windows uninstall process to ensure deferred cleanup completes reliably after application exit.

• Tests

  • Added integration test for Windows uninstall to verify cleanup behavior.

Walkthrough

This PR refactors the Windows self-uninstall helper spawning mechanism. The implementation in spawnWindowsCleanupHelper now uses a cmd /c start "" /b trampoline to launch the PowerShell uninstall helper, replacing the prior Bun detached: true and unref() approach. The new approach spawns cmd via Bun.spawn and awaits subprocess.exited to ensure the helper is actually spawned before returning. Unit test assertions were updated to verify the command structure includes the trampoline and powershell. A new Windows-only integration test was added that validates the deferred executable is removed by the helper after the parent process exits, using a polling waitForMissing helper function.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title follows the required format <type>(<scope>): <subject> with type 'fix', scope 'uninstall', and a clear subject describing the main change of spawning the Windows cleanup helper via cmd start trampoline.
Description check	✅ Passed	The description provides comprehensive context about the Windows uninstall bug, explains the root cause (Bun's kill-on-close job object behavior), details the solution (cmd start trampoline), and references the associated tests and upstream issue.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch fix-win-uninstall

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/application/self-update/uninstall.ts`:
- Around line 498-511: The current awaiting of the Bun.spawn trampoline uses
await subprocess.exited but doesn't check the returned exit code; capture the
resolved exit code from subprocess.exited (e.g., const exitCode = await
subprocess.exited) and if it's non-zero throw an Error with a clear message that
includes the exit code and context (referencing the subprocess variable and the
Bun.spawn call that invoked the Windows bootstrap) so failures of the `cmd /c
start ...` bootstrap fail fast instead of being treated as success.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

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Run ID: e1efa7da-433d-45be-adeb-1f4160992713

📥 Commits

Reviewing files that changed from the base of the PR and between 8d78cb4 and 43290bd.

📒 Files selected for processing (2)

• src/application/self-update/uninstall.test.ts
• src/application/self-update/uninstall.ts