[bug] Bash tool on Windows: TOCTOU race in taskkill /T /F process tree cleanup (orphan leak) #33071

Description

The Bash tool (packages/core/src/tool/bash.ts) creates child processes with detached: process.platform !== "win32" (L163). On Windows, detached is false, so no separate process group is created.

The kill path (packages/core/src/process/cross-spawn-spawner.ts) already has a killGroup function (L292-L312) that uses taskkill /pid ${proc.pid} /T /F on Windows to attempt tree-wide cleanup. However, a TOCTOU (time-of-check-time-of-use) race condition exists: when the shell command (e.g., cmd /c start /b ping -t localhost) spawns a child process, that child may become its own process group leader before taskkill /T enumerates the tree. The /T flag only kills processes that are direct descendants at the moment of execution. If a grandchild process is spawned during the window between shell start and timeout execution, it can escape cleanup.

Additionally, cmd /c combined with start /b creates sibling processes (not children of cmd.exe), which taskkill /T /F may miss because they exist outside the PID-rooted tree.

Steps to reproduce

1. On Windows, ask the model to run: start /b ping -t localhost
2. Wait for the Bash tool timeout (~30s default)
3. The shell process is killed via taskkill /pid <cmd_pid> /T /F, but ping.exe may survive because it was created as a sibling rather than a child of cmd.exe
4. Repeat — multiple orphan ping.exe processes accumulate in Task Manager

Expected behavior

Replace taskkill /T /F with Windows Job Objects (CreateJobObject/AssignProcessToJobObject) to guarantee tree-wide termination regardless of process group topology. Job objects cannot be escaped by child processes and survive across all race conditions.

Code location

• https://github.com/anomalyco/opencode/blob/dev/packages/core/src/tool/bash.ts#L163 (detached flag)
• https://github.com/anomalyco/opencode/blob/dev/packages/core/src/process/cross-spawn-spawner.ts#L292-L312 (killGroup function)

Environment

OpenCode Desktop 1.17.8, Windows 11

About the duplicate flag: The referenced issues cover related Windows process-lifecycle bugs but with different focuses:

• allowed-tools: Bash(agent-browser:*) 衍生的 Chrome 子进程在会话中断后变成孤儿进程 #29856 (orphan child process leak when sessions are interrupted) — similar symptom but the root cause is session interruption, not TOCTOU during timeout-based cleanup
• bash tool hangs when command spawns background child processes #20902 (bash tool hangs when commands spawn background child processes) — about stdout/stderr pipe blocking, not orphan processes
• Bash tool hangs until timeout on Windows when spawned process keeps a stdout/stderr pipe open (dev servers, daemons) #32504 (Windows-specific hang until timeout) — about pipe blocking, same as bash tool hangs when command spawns background child processes #20902

This issue specifically identifies a TOCTOU race in the taskkill /T /F approach and proposes Windows Job Objects as the fix, which is a distinct root cause and solution from the other issues.