Implementing what you describe sounds to me way more "clever" and less robust than the canary page approach described above.
Specifically - I wouldn't fancy writing the "consistently anticipates their adversaries sneaking behind a wall" heuristic you describe but the earlier post describes the API that already exposes the "has read canary page" functionality.
Specifically - I wouldn't fancy writing the "consistently anticipates their adversaries sneaking behind a wall" heuristic you describe but the earlier post describes the API that already exposes the "has read canary page" functionality.