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xarmian 0accca7a40 test(events,docs): pin the detection chain a colliding repair actually relies on (BUG-2740, codex round 5)
The repair seeds from wall-clock seconds, which is above any COUNTED history
and is not a monotonicity guarantee. Corrupt the key twice inside one second
and both repairs seed the same value, so two genuinely different id spaces
carry the identical epoch — and an equal epoch means 'same space' by design,
so neither epoch_change nor epoch_regressed fires.

It is still not silent, and the reason is worth pinning because it is not the
one the epoch mechanism suggests: a merge needs ids REUSED at a receiver,
reuse needs the sequence to go BACKWARDS, and backwards is detected whatever
the epoch says. counter_backward drops the affected buffers and refuses
cursors below the discarded high-water mark.

That was folklore until it was measured. The test drives the whole sequence —
two repairs seeding the same value, a sequence reset between them — and
asserts its own premise first (the two spaces really do share an epoch), that
no epoch-based reason fires, that counter_backward does, and that the old
cursor is refused rather than replayed the new space's events.
Mutation-verified: stop reporting counter_backward and it fails.

The docs carry the chain as a quoted rule, plus the two cases that look like
it and are not — a counter set FORWARD is a jump inside one space with no
reuse, and a receiver that never held the colliding range experiences a gap,
which is BUG-2735's pre-existing class rather than anything this introduces.

Lead re-ruled on the probed fact: residual ACCEPTED because it is detected,
attribution corrected from epoch_regressed to counter_backward.

Claude-Session: https://claude.ai/code/session_01JVDBKbgn3Xt7ndW1YoYd8X
2026-08-23 16:05:44 +00:00
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