audit F47 [quality]: worker_cache test uses std::thread::sleep — flake risk

[intendednull]

File: crates/client/src/worker_cache.rs:176
Severity: quality
Obvious? yes

evict_stale_removes_expired test sleeps 10ms after setting a 1ms TTL. CLAUDE.md's condition-based-waiting skill explicitly flags this as flakey on slow CI.

Fix: inject a clock or expose a cutoff_override for the test to remove the timing dependency entirely.

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Filed by /general-audit @ b901575 (2026-05-02). master: #513.