windows: contain elevated unified exec sessions

[anp-oai]

Intent

Elevated unified-exec sessions must terminate their child tree when the parent requests termination, a timeout fires, or the parent IPC transport disappears. SpawnReady must never describe an uncontained process.

Implementation

• Remove the runner-local best-effort Job Object helper and ignored late assignment.
• Receive an already-assigned JobProcess from both elevated pipe and ConPTY spawn paths.
• Emit SpawnReady only after assignment and resume have succeeded.
• Terminate the shared job on Terminate, timeout, named-pipe EOF, or control read failure.
• Close the job before output-reader joins on normal root exit while preserving the root exit code.
• Add elevated pipe/TTY lifecycle coverage and a real control-transport EOF test.

Manual validation

• Built codex-windows-sandbox and codex-command-runner for Windows gnullvm with Bazel.

Stack

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