core: shell commands run by Git Bash keep running after timeout on Windows #57311

Description

On Windows, a timed out (or aborted) shell command is killed with taskkill /pid <shell> /T /F, which walks the Windows parent/child tree. With Git Bash (MSYS2/Cygwin) that tree is broken: bash starts commands with fork + exec, and on Windows the exec'd program is a new process whose parent (the forked child) exits right away. The program ends up with a dead parent PID, outside the tree, so taskkill reports success and the program keeps running.

Only commands bash forks are affected: anything before ;, pipelines, subshells, background jobs, scripts. The last command of the -c string is exec'd by bash without a fork and still gets killed, so cd x && npm run dev is fine but npm i; npm run dev or npm run dev | tee log is not. Leftovers keep ports and file locks. Might be what #37007 sees on Windows.

The orphans are still in bash's msys process group (checked with msys ps -l), so killing that group with the msys kill -9 -<pgid> before the taskkill would catch them; a Job Object would too.

Plugins

none

OpenCode version

current dev

Steps to reproduce

import { spawn, execSync } from "child_process"
const p = spawn("C:/Program Files/Git/bin/bash.exe", ["-c", "sleep 300; echo done"], { stdio: "ignore" })
setTimeout(() => {
  execSync(`taskkill /pid ${p.pid} /T /F`) // what OpenCode does on timeout
  setTimeout(() => console.log(execSync('tasklist /fi "imagename eq sleep.exe"').toString()), 1000)
}, 1000)
// sleep.exe is still listed; with "sleep 300" alone it is gone

Process tree while it runs:

node
└─ Git\bin\bash.exe
   └─ Git\usr\bin\bash.exe
sleep.exe 300            <- parent PID belongs to an already exited process

Operating System

Windows 11 (22621), Git for Windows 2.52.0

Terminal

n/a (shell tool)