Two defects with one root, found by the fold-checkpoint work's first
integration gate. (1) THE RACE: restore() never quiesced the generation
store, so a background flush could write into _system/ while the swap was
removing it — observed as ENOTEMPTY mid-swap when a checkpoint stamp landed
between readdir and rmdir. The swap now runs inside the store's exclusive
section (runStateReplacement): flush timer disarmed, pending tier and
checkpoint accumulator discarded BEFORE any directory moves. (2) THE
INHERITED ASSERTION: a snapshot carries its source brain's clean-shutdown
marker and fold checkpoint, but the restored files were bulk-copied without
per-file fsync — the inherited stamps would suppress exactly the recovery
fold that cures a post-restore power cut. reopenAfterRestore now deletes
both stamps before reopening: the open treats the store as uncleanly shut,
folds the restored log into canonical, barrier-syncs what it re-applied,
and stamps fresh — the restored state is durably founded at restore time
instead of borrowing assertions about bytes this disk never synced.
Pinned: restore under in-flight traffic completes; the pre-restore stamp
does not survive; the post-restore stamp is the reopen fold's own, at the
restored watermark.
The fold checkpoint (_system/fold-checkpoint.json) is stamped strictly after
a canonical-sync barrier over every live entity touched since the last stamp
(syncEntityCanonical: ids → canonical paths → fsync; an absent file fsyncs
its parent directory so deletes are as durable as writes). An unclean open
under log authority now folds only (checkpoint, head]; the chain bootstraps
at an empty brain's adoption (three-phase hooks around adoptLogAuthority) or
at a brain's first whole-log fold — existing brains converge at their first
crash with zero regression. Rollback restores sync immediately; abort paths
feed the barrier; a failed barrier retains the old bound (bigger fold later,
never a lost write). Five structural pins including boundedness itself.
Also: the production-shaped write-flow gate leg (mixed traffic racing
flushes, crash mid-traffic, every ack survives — from a consumer-reported
gate miss), and two release-ceremony cures (tag-first push so the publish
never queues behind the release commit's CI run; raw-curl npmjs shasum
probe with propagation grace instead of a one-shot false divergence).
