fix(cli): prevent orphaned processes from consuming 100% CPU

[JuanCS-Dev]

Summary

A gemini-cli process becomes orphaned when the parent terminal is closed, enters a CPU spin loop, and runs indefinitely consuming 100% CPU.

Changes

• Added signal handlers for SIGHUP, SIGTERM, and SIGINT to ensure graceful shutdown.
• Implemented setupTtyCheck for interactive sessions to detect lost controlling terminals as a defense-in-depth measure.
• Ensured runExitCleanup() is called on signal-induced exits.
• Cleaned up redundant signal handlers in the main interactive loop.

Fixes #15874

[gemini-code-assist]

Summary of Changes

Hello @JuanCS-Dev, 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 a critical issue where the gemini-cli process could become an orphaned, CPU-intensive runaway process if its parent terminal was closed unexpectedly. The changes introduce robust signal handling and a proactive terminal check to ensure that the CLI application terminates cleanly and efficiently, thereby preventing resource exhaustion and improving overall system stability.

Highlights

• Graceful Shutdown: Implemented signal handlers for SIGHUP, SIGTERM, and SIGINT to ensure the CLI process shuts down gracefully, preventing orphaned processes.
• TTY Check: Added a periodic TTY check (setupTtyCheck) for interactive sessions to detect if the controlling terminal has been lost, serving as a defense-in-depth mechanism against CPU-spinning orphans.
• Cleanup Consistency: Ensured that runExitCleanup() is consistently called when the process exits due to a signal.
• Refactored Signal Handlers: Cleaned up redundant signal handlers in the main interactive loop by consolidating process.stdin.setRawMode cleanup into a generic registerSyncCleanup.

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[gemini-code-assist]

Code Review

This pull request introduces important fixes to prevent orphaned processes from consuming high CPU by adding signal handlers for graceful shutdown and a periodic TTY check. The changes are well-structured, centralizing cleanup logic. I've identified a potential race condition in the new TTY check mechanism and provided a suggestion to resolve it. Overall, this is a solid improvement for the CLI's robustness.

[gemini-code-assist]

There's a potential race condition here. If runExitCleanup() takes longer than the 5-second interval, the setInterval callback could fire again, leading to concurrent shutdown attempts. This can cause unpredictable behavior, especially if cleanup functions are not idempotent.

To prevent this, you should clear the interval as soon as the shutdown process is initiated.

    if (
      !process.stdin.isTTY &&
      !process.stdout.isTTY &&
      !process.env['SANDBOX']
    ) {
      clearInterval(ttyCheckInterval);
      debugLogger.warn('Lost controlling terminal, exiting...');
      try {
        await runExitCleanup();
      } catch (_) {
        // Ignore errors during cleanup
      }
      process.exit(ExitCodes.SUCCESS);
    }

[scidomino]

Closing as this PR is redundant as the proposed changes (signal handlers and TTY check) are already implemented in packages/cli/src/utils/cleanup.ts