windows: contain local ConPTY sessions

[anp-oai]

Intent

Local Windows ConPTY sessions must end the entire process tree when the root shell exits, the session is terminated, or the session handle is dropped. Descendants must not keep the session alive or escape after its reported completion.

Implementation

• Create and configure the Job Object before CreateProcessW.
• Spawn the ConPTY root suspended, assign it to the job, and only then resume its primary thread.
• Make WinChild own JobProcess while cloned killers retain only the shared job controller.
• Close the job before returning the root exit status and terminate the job for explicit kill paths.
• Add focused exit-code, termination, natural-root-exit, and session-drop coverage.

Manual validation

• Cross-compiled the codex-utils-pty Windows test target with cargo +1.95.0 check --target x86_64-pc-windows-msvc -p codex-utils-pty --tests.

Stack

1. job primitives → 2. local ConPTY → 3. restricted sessions → 4. elevated runner → 5. command preparation → 6. raw pipe launcher → 7. command parity