A new utility skill that grades a finished session on three axes —
cost & efficiency, toolchain health, agent effectiveness — from the
session's own Claude Code flight recorder (the JSONL transcript plus
one sidechain log per dispatched subagent).
The heavy lifting lives in scripts/postmortem.py, a stdlib-only,
read-only aggregator. It handles the two accounting traps the raw log
sets: usage is repeated per streamed assistant line under a shared
requestId (deduped max-per-field, then summed across requests), and
the transcript carries no costUSD/durationMs (both null) — so cost is
derived from tokens x an overridable list-price table and labelled an
estimate, wall-clock from timestamp deltas. Subagent spend is billed
separately from its own usage objects and graded by terminal status.
Single-session by design: defaults to the newest transcript in the
project's log dir (flagged active if still live), or --session <id>
for a finished run. Secret files are out of bounds in both the Iron
Law and the Red Flags.
Verified end-to-end against a real 15-subagent session.
