Avoid signaling recycled process groups

[austinywang]

After the direct child has been reaped, stop trusting its cached numeric process-group id because the kernel may reuse it. Teardown now signals only a foreground group freshly observed through the retained PTY. Includes regression coverage for an unrelated cached group and for reaping a distinct foreground job after the leader has genuinely exited.

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Summary by cubic

Prevents teardown from signaling a recycled process group after the child is reaped. Now we only stop the foreground group read from the retained PTY, avoiding signals to unrelated jobs.

• Bug Fixes
  • Stop trusting cached process_group_id once the child is reaped; use fresh foreground_process_group_id from the PTY.
  • Switch to killProcessGroupWithTimeouts to target only the active foreground group.
  • Add regression tests for ignoring stale groups and for killing a distinct foreground job after the leader exits.

^{Written for commit bc7e9f7. Summary will update on new commits.}

Summary by CodeRabbit

• Bug Fixes
  • Improved subprocess cleanup after a process exits.
  • Prevented teardown from targeting stale process information, reducing the risk of terminating unrelated foreground processes.
  • Ensured remaining subprocesses are consistently cleaned up when their leader exits.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 3a1827d3-cefa-49ba-a7ea-763b464e6521

📥 Commits

Reviewing files that changed from the base of the PR and between f66cfbd and bc7e9f7.

📒 Files selected for processing (1)

• src/termio/Exec.zig

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📝 Walkthrough

Walkthrough

Teardown now avoids stale cached process-group IDs after child reaping. New tests verify that unrelated groups remain alive and that foreground descendants are cleaned up after synchronous leader reaping.

Changes

Process-group teardown safety

Layer / File(s)	Summary
Foreground process-group teardown src/termio/Exec.zig	Teardown uses the foreground process group from the retained PTY when the process is externally absent.
Reaping and descendant cleanup tests src/termio/Exec.zig	Tests cover stale cached groups and synchronous reaping before teardown. The distinct foreground-group test removes its concurrent reaper thread.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• manaflow-ai/ghostty#192: Both changes update src/termio/Exec.zig teardown and process-reaping tests.

Suggested reviewers: mitchellh, rockorager

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch issue-9573-pgid-reuse-safety

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