fix(opencode): run tui worker shutdown on signal/terminal-exit paths

[s2bomb]

Fixes #14237

What does this PR do?

Ensures the TUI command routes process-exit signals through the existing worker
shutdown path, instead of only cleaning up during normal UI exit.

Why this change

thread.ts calls client.call("shutdown") only inside onExit. There are no
handlers for SIGINT, SIGTERM, or SIGHUP, so signal-based exits skip worker
cleanup and child resources can survive.

worker.ts already has the canonical cleanup (Instance.disposeAll() with timeout

• server.stop(true)). This patch reliably invokes that existing logic from all
  exit paths.

Changes

packages/opencode/src/cli/cmd/tui/thread.ts — one idempotent shutdown wrapper
with a 5s timeout, signal handlers for SIGINT/SIGTERM/SIGHUP, and onExit
routed through the same path. Mirrors signal-driven shutdown already used in other
command entrypoints. No new cleanup semantics introduced.

How did you verify your code works?

Reproduced leak before fix using a deterministic harness (local fake MCP server
under script -q -c), then verified clean exit after fix:

# start TUI under pseudo-terminal host
script -q -c "opencode /tmp/repro-project" /tmp/tui.log &
# send SIGHUP to TUI process
kill -HUP "$(pgrep -f 'opencode /tmp/repro-project')"
# confirm clean exit (exit code 0, no surviving children)

Full test suite: bun test --timeout 30000 in packages/opencode — 1095 pass,
5 skip, 0 fail.

[github-actions]

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[github-actions]

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[github-actions]

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

Potential Duplicate PRs Found

Based on the search results, here are related PRs that may be addressing similar issues:

1. 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: Adds signal handlers to TUI to prevent orphaned processes, which is very similar to the current PR's goal of handling SIGINT/SIGTERM/SIGHUP

2. fix(cli): handle SIGHUP to prevent orphaned processes on terminal close #12718 - fix(cli): handle SIGHUP to prevent orphaned processes on terminal close

   • Related: Specifically handles SIGHUP in CLI to prevent orphaned processes, overlaps with signal handling approach in current PR

3. fix: resolve memory leaks and zombie processes from missing cleanup handlers #13186 - fix: resolve memory leaks and zombie processes from missing cleanup handlers

   • Related: Addresses the same problem of missing cleanup handlers causing zombie processes and resource leaks

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

   • Related: Directly addresses preventing orphaned worker processes

Recommendation: Check PR #13848 first, as it appears to be the most directly related to TUI signal handling. Verify if it already covers the current PR's scope or if this PR addresses remaining gaps.

[s2bomb]

Closing — this duplicates #13848 (and partially #12718), which I discovered after submission. Will comment there instead.