Worker-ready wait reused Bun's 5s default per-test timeout as its floor, so a slow cold-start under --isolate + high CI concurrency was aborted at 5s. The catch then terminate()s a still-initializing Bun worker -- the documented SIGILL/SIGTRAP crash trigger -- crashing the whole test file and intermittently failing unrelated PRs.
Introduce WORKER_INIT_TIMEOUT_MS=15s as a fixed infrastructure floor (independent of, still dominated by, a larger per-cell timeout) and set a 20s file-local setDefaultTimeout in js-executor/js-workflow-helpers tests so cold starts complete instead of being torn down.