High-frequency marker.matches shared the single project notification queue with topology events (node.*/link.*), causing head-of-line blocking. Add a separate marker channel: Notification.project_marker_queue/marker_emit, dispatch routes marker.* off the main project queue, plus a new WS /{project_id}/notifications/markers/ws endpoint. Fully migrated (the main project WS no longer carries marker.match); marker listeners are independent of project auto_close. Compute side unchanged.
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