fleet-write: apply write-pace rule 5 on the runner for a batched stroke

The executor announces ONE rule-5 batch before the first write when a
stroke carries DEFAULT_BATCH_THRESHOLD or more content-creating actions,
so those writes leave DEFAULT_BATCH_GAP_MS apart instead of rule 1's 3 s.
The content-creating set is read off the op table (createsContent), the
pacing has one spelling (strokePacing) shared by the packer, the
run-poller and the executor; a stroke whose pacing the relay job cannot
hold is refused at the packer and again at the executor with zero writes,
naming the per-op doors; the seat waits for a batched run as long as the
runner is told to pause.

Claude-Session: https://claude.ai/code/session_01HEdP5tPhqQfzwRmKDxwn85
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude