The extraction pipeline stops re-reading whole sessions: coverage is a
per-chat covered-fingerprint ledger at MESSAGE granularity (tool call and
result never separated — they share a message; quiz events not special —
they ride re-opened messages normally), uncovered content is derived at
read time (never dual-tracked), the trigger becomes uncovered tokens >= a
chunk budget (fixing quiz-less sessions that never extract), and runs
checkpoint coverage incrementally per merged batch — abort/error loses
at most one in-flight batch. Manual extract-the-rest falls out of the
diff. Pointer line under vision.md 'Construction'.
