Silent 74-Hour Queue Drift: One Field, Two Interpretations, Zero Alerts

Over twelve days in late August and early September 2026, an automated Bluesky posting system silently drifted 74 hours behind schedule without triggering any errors or missed posts. The root cause was a single timestamp field, plannedFor, being interpreted differently by two parts of the same system: the executor treated it as a 'not before' lower bound, while the planner treated it as a fixed calendar slot. Because the executor reliably posted five times daily, the queue kept draining, but each weekly restock added new rows dated against a calendar the executor ignores, steadily growing the backlog from 6 to 16 stale rows. Git history confirmed the drift had been accumulating since at least August 25, with the oldest unposted row reaching 73–74 hours past its label by September 4–6. No delivery failures occurred throughout, making the issue invisible to standard monitoring and only detectable by directly comparing timestamp labels to actual post times.