fix: handle SIGHUP/SIGTERM/SIGPIPE to prevent orphaned processes

[kevinWangSheng]

Issue for this PR

Closes #14504

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds signal handlers for SIGHUP, SIGTERM, and SIGPIPE that call process.exit(1). Without these, when a terminal dies (SSH disconnect, tmux pane close), opencode processes become orphaned because cli.parse() never resolves and process.exit() in the finally block never runs. Each orphan leaks ~4.7 GB of RAM.

How did you verify your code works?

Reviewed the 3-line change. process.on(sig, () => process.exit(1)) triggers the existing finally-block cleanup. All CI checks pass.

Screenshots / recordings

N/A - no UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate PRs Found

Several related PRs exist that address similar orphaned process issues:

1. PR fix(tui): add signal handlers to prevent orphaned processes on terminal close #13848 - fix(tui): add signal handlers to prevent orphaned processes on terminal close - Directly related, handles signal handlers for the same issue

2. PR fix: resolve memory leaks and zombie processes from missing cleanup handlers #13186 - fix: resolve memory leaks and zombie processes from missing cleanup handlers - Addresses cleanup handler issues that prevent zombie processes

3. PR fix: add signal handlers to prevent orphaned processes #12877 - fix: add signal handlers to prevent orphaned processes - Similar signal handler approach

4. PR fix(cli): handle SIGHUP to prevent orphaned processes on terminal close #12718 - fix(cli): handle SIGHUP to prevent orphaned processes on terminal close - Specifically handles SIGHUP for terminal close scenarios

5. PR fix(tui): graceful exit on Ctrl+C and resolve multiline paste corruption #14440 - fix(tui): graceful exit on Ctrl+C and resolve multiline paste corruption - Related to signal handling and graceful exit

Recommendation: Check if any of these existing PRs (especially #13848, #13186, or #12877) already implement similar signal handler logic. PR #14548 may be duplicating work if these weren't merged or completely address the same issue.

[github-actions]

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