- One run per host: start_run claims every host it touches (addresses read from the inventory Steward wrote; a source's own inventory file is claimed as that file) before it takes a run slot. The claim is all-or-nothing. A run waiting on a host shows queued and names the run it waits for, honours a cancel, and fails after HOST_WAIT_SECONDS (1 h) with which host and run. - A due schedule whose previous run is still queued or running skips the firing: last_run_at moves on, last_run_id still names the run going, and last_error says "Skipped: the previous run was still going". The Schedules page shows that beside the run (muted), and a launch error in red. - An alert rule that fires while the action run from an earlier firing is still going starts no new run; the event says so and names the run. An in-process set closes the gap between the check and the run being linked. - docs/core/ansible.md: queued/cancelled statuses and the overlap rules. Tests: tests/core/test_ansible_overlap.py (claim keys, waiting, all-or-nothing, cancel, deadline) and tests/integration/test_ansible_overlap.py (two real runs on one host take turns; schedule skip then fire; alert action skip then start). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>