Tool success is not evidence: the quiet agent failure mode nobody checks
Key-Register-1969 · reddit · 2026-11-03
The author argues that while most agent failure discussions focus on bad reasoning, the quieter failure is bad evidence: a tool returns "success" (meaning accepted/queued/no error), the agent reports done, and nobody verifies the system that owns the result. Partial writes, async queues, and silent default substitution all pass tool-level checks while leaving the destination state wrong.
The proposed pattern: treat every consequential write as unverified until a separate read from the system of record confirms the expected state under the expected ID. If the read can't run yet, the task is deferred, not done, with a recheck time and owner.
Two named failure modes: reading back through the same wrapper that wrote the data proves nothing (use a different path); and existence-only read-backs pass on partial writes — check the fields that matter or at least sample them. Open question: should every write get a read-back, or only irreversible/externally visible ones?
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