fix(cli): forward termination signals to relaunched child process

[ixchio]

This one's been bugging me — when you kill the parent process, the child just... keeps running.

The problem

relaunchAppInChildProcess spawns a child but never forwards SIGTERM, SIGHUP, or SIGINT. So if a process manager (or just kill <pid>) sends a signal to the parent, the child becomes an orphan. Pretty annoying in containers and ACP setups.

What I did

• Added signal forwarder handlers right after spawn() for SIGTERM, SIGHUP, and SIGINT
• Each handler checks child.killed before forwarding (no point sending signals to a dead process)
• Forwarders get cleaned up on both close and error events
• Wrapped child.send() in try/catch — if the IPC channel is already dead when we try to send admin settings, we don't want that to leak the signal handlers

Why not PR #25605?

That PR had a couple issues the reviewers flagged:

• Conditional !process.stdin.isTTY check that re-introduces the leak for programmatic kill -INT
• Inaccurate comments about Ctrl+C behavior
• Potential listener leak if child.send() throws before promise setup

This PR forwards unconditionally and handles the cleanup properly.

Tests

Added 4 tests:

• SIGTERM gets forwarded to child
• Signal forwarders get registered on spawn
• Forwarders get removed after child closes
• Signals are skipped when child is already killed

Test Files  1 passed (1)
     Tests  12 passed (12)

Fixes #25590

cc @scidomino @jacob314 would love your eyes on this

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses an issue where child processes spawned by the CLI become orphaned when the parent process is terminated. By explicitly forwarding termination signals and ensuring proper cleanup of event listeners, the changes ensure that the child process lifecycle is correctly tied to the parent, improving stability in containerized and automated environments.

Highlights

• Signal Forwarding: Implemented signal forwarding for SIGTERM, SIGHUP, and SIGINT from the parent process to the child process to prevent orphaned processes.
• Resource Cleanup: Added automatic cleanup of signal listeners upon child process termination or error to prevent memory leaks.
• IPC Robustness: Wrapped IPC communication in try/catch blocks to ensure signal handlers are correctly managed even if the IPC channel is closed.

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[gemini-code-assist]

Code Review

This pull request implements signal forwarding from the parent process to the child process in relaunchAppInChildProcess to prevent orphaned processes, including listener cleanup and improved IPC error handling. Feedback suggests removing the !child.killed guard to allow for signal escalation (e.g., sending SIGTERM after SIGINT) and reordering the message listener registration to ensure it is active before the initial child.send() call. The test suite should also be updated to reflect these logic improvements.