## Why
Terminating a Windows execution session must also stop child processes, while a
normal root-process exit must continue to allow background descendants to run.
## What changed
- Assign Windows pipe, ConPTY, and sandbox processes to job objects and terminate
the job when a session is cancelled, times out, or is explicitly stopped.
- Preserve descendants when the root process exits normally.
- Attach ConPTY and sandbox processes to their jobs atomically at creation; keep
root-process termination as a fallback where job setup is unavailable.
## Testing
Added Windows coverage for descendant termination and preservation across pipe,
ConPTY, capture, cancellation, and legacy sandbox execution paths.
GitOrigin-RevId: 8f831f2fc4caaa7b79ce842a3ed7192bd02dd3b4
iceweasel-oai
9b33613db6