Delay pending cleanup until task aborts

[aibrahim-oai]

Summary

• move interrupted-turn cleanup so running tasks are aborted before pending approvals are cleared
• keep unified exec shutdown behavior unchanged

Why this fixes the flake

The interrupted-turn path could clear pending approvals before the in-flight task had observed cancellation. On slower runners that let an approval wait resolve in between those steps, tests would sometimes surface a model-visible rejection instead of the expected TurnAborted flow. Draining the active turn first and only then clearing pending approval state makes the abort ordering deterministic.