#236 test: bound fs-lock contender cleanup

Summary

Post-merge follow-up to #235 after independent review found that its timeout branch still performed an unbounded worker join.

This tightens the test lifecycle without changing production locking:

• wait for an explicit contender-start handshake before beginning the result watchdog
• distinguish worker disconnection from a real result timeout
• keep the owner live throughout the bounded result window
• after timeout, drop the owner only for cleanup and use a second bounded wait; a persistently stuck worker is detached instead of hanging the test process
• tolerate sender teardown on timeout paths

Verification

• cargo +1.93.0 fmt --all -- --check
• cargo +1.93.0 test -p agent-file-tools --lib fs_lock::tests — 21 passed
• focused test repeated 100 times with a 20-second outer process timeout — 100 passed

The commit is SSH-signed and based on current main at 24744afe.

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Summary by cubic

Bounds fs-lock test cleanup to avoid unbounded joins when a contender blocks. The old test could hang on timeout; the new test uses handshakes and bounded waits without changing production lock behavior.

• Adds a contender-start handshake (5s) before the watchdog and a bounded result wait (2s); distinguishes disconnection from timeout with clear panics.
• On timeout, keeps the owner live during the wait, then drops it only for cleanup, performs one more bounded wait (1s), and does not join a stuck worker to prevent hanging the test process.

Greptile Summary

This PR bounds cleanup in the filesystem-lock contention test so a stuck worker cannot hang the test process.

• Adds an explicit handshake before starting the result timeout.
• Distinguishes worker disconnection from timeout.
• Releases the owner only during cleanup and bounds the second wait before detaching a persistently stuck worker.

Confidence Score: 5/5

The PR appears safe to merge because the changed test cleanup is bounded and does not alter production lock behavior.

The contender-start handshake preserves the intended live-owner test window, disconnection is handled separately, and both timeout waits are bounded so the regression test cannot hang indefinitely during worker cleanup.

Important Files Changed

Filename	Overview
crates/aft/src/fs_lock.rs	Tightens test-only thread synchronization and timeout cleanup without changing production locking behavior; no actionable defect was identified.

_{Reviews (1): Last reviewed commit: "test: bound fs-lock contender cleanup" | Re-trigger Greptile}