test/hand-decider.test.ts throws no unhandled error: every run of the file ends with each test named #5700

For: the check reported test/hand-decider.test.ts > let the decider answer a hand-over > (unnamed) on pull #5628, which only moved one sentence between two files. That label means an error escaped the tests, from a hook, a timer or an unawaited promise, and it fails pulls that never touched the decider.

Done:

• [ ] Find what escapes: bun test --rerun-each 30 test/hand-decider.test.ts reproduces it, or the pull says it didn't, with the counts. Fix the cause: await the promise, close what the file opens in afterAll, clear the timer, or fix src/ if the product throws.
• [ ] 30 runs in a row pass with no (unnamed) failure.
• [ ] Nothing the tests promise is weakened: no retries, no skipped cases, no longer timeouts.

Files: test/hand-decider.test.ts and the module the cause is in. See #5667 and #5695 for the same failure in two other files; if the cause is shared (a helper in test/helpers/), fix it once and say so on all three.

Planner: the same (unnamed) failure now also appears in test/pull-merge-box.test.ts (#5719). Four files in all: #5667, #5695, #5700, #5719. Check for one shared cause, such as a helper in test/helpers/ or a server that outlives its file, before fixing this file alone.