fix(cli): handle SIGHUP to prevent orphaned processes on terminal close

[shjeong92]

What does this PR do?

Fixes #10563, relates to #11225, #11527

When a terminal tab/window is closed, the OS sends SIGHUP to the process group. OpenCode has no SIGHUP handler, so the process ignores it and stays alive as an orphan under launchd (PPID=1), consuming memory indefinitely.

This adds SIGHUP and SIGTERM handlers to all long-running entry points:

• index.ts: Safety net with 3s timeout fallback (covers all commands)
• thread.ts: Graceful worker shutdown before exit (TUI mode)
• worker.ts: Shutdown + ppid polling to detect parent death (safety net for SIGKILL)
• attach.ts: Exit on signal (opencode attach mode)
• serve.ts: Exit on signal (opencode serve mode)

The layered approach works like this: command-specific handlers do graceful cleanup and exit immediately, while the index.ts safety net force-exits after 3s if a command-specific handler hangs.

How did you verify your code works?

• All 897 existing tests pass, 0 regressions
• tsc --noEmit passes with no type errors
• Added signal handling tests that spawn actual opencode serve, send SIGHUP/SIGTERM, and verify graceful exit (exit code 0 vs 129 without fix)
• Manual test: start opencode, note PID, send kill -HUP <pid>, confirm process exits

[github-actions]

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

Based on my search, here are the related PRs that might be duplicates or closely related:

Potentially Related PRs

1. fix: prevent orphaned worker process when killed #11603 - fix: prevent orphaned worker process when killed

   • fix: prevent orphaned worker process when killed #11603
   • Directly addresses orphaned worker processes, similar issue scope

2. fix: force kill MCP server processes on dispose to prevent orphan processes #7424 - fix: force kill MCP server processes on dispose to prevent orphan processes

   • fix: force kill MCP server processes on dispose to prevent orphan processes #7424
   • Handles orphaned process prevention through proper cleanup

3. fix(pty): use proper process tree cleanup on disposal #5876 - fix(pty): use proper process tree cleanup on disposal

   • fix(pty): use proper process tree cleanup on disposal #5876
   • Related to process cleanup and signal handling

Note: PR #12718 (the current PR) appears to be a comprehensive solution addressing the same orphaned process issue that previous PRs have attempted to fix. Check if #11603 and #7424 are closed/merged and whether this PR supersedes them or if there's overlapping work.

[luisrudge]

yeah I was just hit with this issue as well.

You have 68 opencode processes running, most dating back to Jan 28 - Feb 1. This happens when you close terminal windows without explicitly exiting opencode (Ctrl+C or /exit) - the processes keep running in the background.
These are consuming:

• ~10-15% total CPU (even while idle)
• ~8GB+ RAM combined
  To clean them up, you can kill all except the current session:

Kill all opencode processes except the current one (PID 76275)

ps aux | grep opencode | grep -v grep | grep -v 76275 | awk '{print $2}' | xargs kill