test/checks.test.ts runs under 10 s #3494

Measured 2026-10-20 in a builder sandbox: bun test test/checks.test.ts takes 25.5 s for 37 tests, over the 10 s a file the owner set (#1242).

Done:

• [ ] The pull names the five slowest tests with their times before and after.
• [ ] Each slow test waits on an event or calls the step directly in place of sleeping or polling a tick; no assertion is weakened or removed.
• [ ] The file runs under 10 s locally; if it can only by splitting, the new file is picked up by the gate's discovery and the pull says so.

Files: test/checks.test.ts (and a split file if needed). Change src/ only for a test seam, named in the pull.