test(coding-agent): bounded streaming-abort verdict drains by wall time

- The 400 zero-delay setImmediate drains starved under parallel CI load:
  the guard's verdict needs real wall time (2MB target disk read plus
  Bun.sleep(0) slice timers), and an immediate-only spin burns its whole
  tick budget in under a millisecond without firing either.
- Poll the verdict with a deadline-bounded 1ms sleep instead, mirroring
  the collab settle-loop fix in a4dbcda37a.