flaky: two order/timing-dependent tests can fail the CI gate on unmodified trees

[kjgbot]

Two tests intermittently fail on trees that pass 967-973/973 on rerun, both reproduced on unmodified bases (2026-08-25):

1. src/__tests__/workflow-runner.test.ts > should not double release the worker when the owner fails after worker completion — order-dependent and environment-sensitive; paired control on ci: gate pull requests on tests and typecheck #42 showed 1 failed | 75 passed on unmodified base 475e25e vs 76 passed with the branch. Leaked agent-relay-broker processes are the leading suspect (11 alive during the failing run).
2. src/__tests__/completion-pipeline.test.ts > happy-path lead-worker workflow proof > should still complete when WORKER_DONE lands after the lead checks the work — failed (expected 'failed' to be 'completed') on feat(core): add explicit terminal-success exits #39's merge head 8213297 in CI run 32849908822, passed on rerun of the identical tree.

Now that PRs are CI-gated (#42), an intermittently-red gate trains people to merge past red. Both tests need to be made hermetic (broker process isolation / deterministic completion-signal ordering) or quarantined with a tracking note.