Codex final-gate found the boundary<watermark advanced signal made
sidecar_advanced_past_watermark globally true, so a stale ts>watermark suffix
row appearing in state.db BEFORE the edited checkpoint bypassed the skip and
resurrected. Gate the bypass on state_replay_idx >= len(sidecar_visible_sequence)
(checkpoint consumed); apply the same gate to the same-second CORE-B exception.
Regression test added + proven non-vacuous. All legit cases (state-only reply
after checkpoint, CORE-B same-second) still pass.
Co-authored-by: AlexeyDsov <alexeydsov@gmail.com>
Final-gate Codex repro found a non-empty-sidecar drop: when the post-edit USER
turn is checkpointed into the sidecar (ts == advanced watermark) but its
ASSISTANT reply exists only in state.db (ts > watermark), the
sidecar_advanced_past_watermark guard was False (max_sidecar_timestamp ==
watermark, not >), so the 'timestamp > watermark' skip dropped the legitimate
reply. GET /api/session returned ['first','first reply','edited prompt'] and
omitted the assistant.
Fix: treat truncation_boundary < watermark (genuinely advanced) as advanced too,
so post-watermark state-only rows merge through even when the sidecar tail only
EQUALS the watermark. Conservative skip preserved for boundary None / == watermark.
Hoisted the loop-invariant boundary check out of the per-message loop. Regression
test added + proven non-vacuous.
Co-authored-by: AlexeyDsov <alexeydsov@gmail.com>
Opus deep-gate found a latent data-loss the Codex harnesses missed: the
empty-sidecar branch kept at_or_after (ts>=watermark) UNCONDITIONALLY, which is
only valid once the watermark was ADVANCED strictly past the original cutoff
(a new turn committed -> boundary < watermark). In the not-advanced states the
content above the watermark is the deleted suffix, so it got resurrected — the
same data-loss class this fix exists to kill. Reachable via crash/cold-load
metadata-vs-sidecar divergence.
- Keep at_or_after ONLY when boundary < watermark (genuinely advanced).
- boundary == watermark (just truncated) OR boundary is None (legacy: a positive
watermark always meant 'frozen at cutoff' pre-#4767) -> conservative ts<=watermark
filter; never resurrects.
- Replaced the backward-scan heuristic with the provable boundary guard.
- Removed the now-dead 'or (not sidecar_messages and watermark>0)' clause in the
non-empty-sidecar path (unreachable; empty sidecar returns earlier).
- Added 2 regression tests (boundary==watermark, legacy None-boundary), both proven
non-vacuous; updated 2 contributor tests that assumed advanced-watermark-without-boundary
(an unreachable state) to pass the boundary the real persistence path always writes.
Co-authored-by: AlexeyDsov <alexeydsov@gmail.com>
