fix(core): stop the bash tool from hanging forever when a child holds the pipe - #349

Problem

executeShellCommand only settled its promise inside the child's 'close' event. 'close' fires when the process and its stdio pipes are done, so a backgrounded descendant keeps it from ever firing:

• cmd &, nohup ... & — the & backgrounds the whole && list, and the detached subshell inherits this tool call's stdout/stderr pipes.
• The shell exits, the descendant keeps the pipes open, 'close' never arrives.
• The timeout path called killProcessTree(pid) only, which is a no-op once the shell pid is gone (taskkill /PID <pid> /T /F exits 128), and it did not settle the promise either.

Net effect: resolve() never ran, so the tool call never returned and the whole CLI session wedged permanently. Observed 2026-09-13 23:44; the machine had to be hard-powered-off.

A safe-looking command is enough to trigger it:

cd repo && rm -f out.txt && nohup sh run.sh >/dev/null 2>&1 & sleep 25; echo progress

Fix

• Settle unconditionally 2s after the timeout kill, and 2s after the child's 'exit' event (a new 'exit' handler), destroying the stdout/stderr pipes on the way out. 'exit' fires when the process is gone, before/without 'close'.
• Ignore a late 'close' once settled, and keep the timeout status instead of letting a late 'exit' report exitCode: 0 for a command that was actually killed.
• Append a note to the output telling the model to use run_in_background: true for detached work, so the next call does not repeat the pattern.

Detached work is unaffected: only the tool call settles early; the background process keeps running.

Tests

packages/core/src/tests/tool-handlers.test.ts — new case "Bash settles when a background descendant keeps the output pipe open":

sleep 5 & printf 'hi\n'

sleep 5 & inherits the pipes and outlives the shell. With a 60s configured timeout the call must still return in a few seconds, report ok, include the note, and emit exactly one onProcessExit.

node --import tsx --test --test-concurrency=1 packages/core/src/tests/tool-handlers.test.ts
→ 4 tests / 4 pass
(held-pipe case settles in ~2.1s; existing timeout + background cases unchanged)

tsc --noEmit is clean.