test/pull-merge-box.test.ts throws no unhandled error: every run of the file ends with each test named #5719

For: the check reported test/pull-merge-box.test.ts > (unnamed) on pull #5716, which only moved two sentences. An error escaped the tests, from a hook, a timer or an unawaited promise, and it fails pulls that never touched the merge box.

Done:

• [ ] Find what escapes: bun test --rerun-each 30 test/pull-merge-box.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.

Files: test/pull-merge-box.test.ts and the module the cause is in. The same failure is open in three other files: #5667 (explore-rank), #5695 (tui-sentinel), #5700 (hand-decider). Look for one shared cause first, such as a helper in test/helpers/ or a server that outlives its file. If you find it, fix it once and say so on all four.