test/explore-rank.test.ts throws no unhandled error: every run of the file ends with each test named, pass or fail #5667

For: the check reported test/explore-rank.test.ts > (unnamed) twice in a row on pulls that never touched explore (#5633, #5640). That label means an error escaped every test, from a hook, a timer or an unawaited promise. It fails unrelated pulls, and no named test says why.

Done:

• [ ] Find what escapes: bun test --rerun-each 30 test/explore-rank.test.ts reproduces it, or the pull says it didn't, with the run counts. Then fix the cause: await the promise, close the server or database in afterAll, clear the timer, or fix the product if the error is thrown by src/.
• [ ] 30 runs in a row pass with no (unnamed) failure.
• [ ] Nothing the tests promise is weakened: no retries, no skipped or deleted cases, no longer timeouts.

Files: test/explore-rank.test.ts and the module the cause is in. Why now: two pulls closed on it.

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.