Honor planned restart continuation for app-started chats

[hamzamerzic]

Summary

• honor Continue after planned restarts for app-started chats
• preserve the initiating app on the resumed run unless newer owner input has taken control
• keep provider-limit retries and newly queued app work on their existing manual path

Why

This follows the authenticated planned-restart boundary introduced in #157, the independent default-on restart policy from #168, and the exact handoff recovery expanded in #304. Those changes retained an older app-attribution exclusion, so an app-started chat could show restart continuation as enabled yet still stop after a planned restart.

This follow-up removes only that stale exception. It does not turn provider-limit retries into background app work or absorb app messages queued after the parked run.

Safety

Automatic continuation still requires the latest exact restart park, the current boot's supervisor-authenticated nonce, the per-chat restart policy, and no unanswered question. The resumed turn uses the existing pending-message attribution path. A newer owner message becomes the next run's actor; later app work stays manual.

Testing

• complete backend suite before the final upstream refresh: 3,469 passed, 1 skipped
• focused restart, app-chat, writer, transcript, and proxy suites after the final rebase: 202 passed
• Python compilation and diff checks passed