#460 Windows deferred bash wait test: wait for the deferral itself, not a startup deadline

Accepted agent delivery; branch-keyed search descriptor included.

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Summary by cubic

Fixes the Windows deferred bash wait test so it waits for the deferred wait to actually enter instead of racing shell startup deadlines.

• Replaces the 10-second startup budget and separate 3-second startup check with a single 120-second hang cap, applied only in this test; no product timeouts change.
• Panics if the bash command completes before the wait enters, and rejects tasks already terminal before lock contention, so the held-lock observation is always exercised.
• Adds a benchmark descriptor for the land-deferred-wait-causal slice.

Confidence Score: 5/5

The PR appears safe to merge.

Summary

Updates the deferred Bash wait test to allow slow Windows shell startup without relaxing its frame-loop check.

• The Bash wait test measures responsiveness only after the wait enters.

_{Reviews (1) · Last reviewed commit: "landing: describe deferred-wait-causal" · Reviewed by Greptile}