The most expensive agent bug isn't hallucination — it's "claimed done"
kushagra_zryth · reddit · 2026-10-30
From building production agents (clinic voice booking, outreach, flour-mill automation), the author argues the costliest failure mode is agents claiming success when writes silently failed — "appointment booked" when the calendar write never landed.
His playbook:
- Read back after every write: don't trust the tool call's success message; fetch the record and verify
- Separate "claimed" from "verified" in logs: two states; most dashboards only show the first
- Confirm to humans only after verification: a short "one sec, confirming" beats a fast wrong "you're booked"
- Turn every failure into a task, not a silent retry: failed bookings become human callbacks with context
- Idempotency keys on anything that sends or books: retries happen; double bookings shouldn't
It's maybe 20% of the code, but it decides whether the business keeps the agent after week two.
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