fix(desktop): stop out-of-band ancestor merges from poisoning the scrollback cursor#1483
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fix(desktop): stop out-of-band ancestor merges from poisoning the scrollback cursor#1483tlongwell-block wants to merge 3 commits into
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…ollback cursor The older-history pager anchored its until cursor on baseline[0] — the oldest event in the channel cache — assuming the cache is contiguous. It is not: useLoadMissingAncestors injects thread roots fetched by id, and useThreadReplies injects whole reply subtrees, both of which can be days older than the contiguously loaded window. With such an island in cache, the next scroll-up fetch pages backward from the island and the history between the island and the real frontier is never requested. Every later pass anchors on the even-older result, so the hole never heals — the June 14 → June 9 day-skip, with June 12 sometimes partially present (the injected roots themselves). Fix: out-of-band merges mark what they splice in (RelayEvent.nonContiguous, local-only), and the pager anchors on the oldest UNmarked content event (oldestContiguousHistoryTimestamp). The state rides on the event, so it is atomic with the cache write, survives trims, and heals itself: when contiguous paging reaches an island, the history merge's last-copy-wins dedupe replaces the flagged copy with the fresh unflagged one. The dense-second keyset seed skips flagged events for the same reason — an island at the boundary second is a point, not a fetched prefix. Regression tests drive the real pager (runPageOlderPass) against a relay double: red on the previous anchor (island skips the gap days), green on the frontier anchor, plus island healing and the all-islands fallback. Also verified end-to-end under node against the full 2,980-event #buzz-bugs dataset: previously June 11 was missing entirely and June 12/13 reduced to injected fragments; with the fix every day from the frontier renders and zero relay events in the fetched span are absent from the cache. Co-authored-by: Tyler Longwell <tlongwell@block.xyz> Signed-off-by: Tyler Longwell <tlongwell@block.xyz>
An ancestor/thread fetch can start while an event is missing, a contiguous history page can fetch that same id unmarked, and the late out-of-band response then merges for an id that is now contiguous. mergeNonContiguousTimelineMessages must treat that as a no-op (it filters incoming ids already in cache before marking), or the frontier that contiguous paging just advanced gets re-poisoned. Pin that invariant with a test. Co-authored-by: Tyler Longwell <tlongwell@block.xyz> Signed-off-by: Tyler Longwell <tlongwell@block.xyz>
maxEventIdAtSecond seeded the bridge composite cursor from every cached event at the boundary second, but the bridge keyset pages timeline- content kinds only. An unmarked reaction/edit/deletion at that second with an id later than the held content prefix would seed before_id past unseen content rows — a same-second hole. Apply the same isTimelineWindowContentEvent predicate the frontier helper uses, and pin it with a regression (aux and island ids at the boundary second are both ignored; all-aux yields no fabricated cursor). Found in review by Wren. Co-authored-by: Tyler Longwell <tlongwell@block.xyz> Signed-off-by: Tyler Longwell <tlongwell@block.xyz>
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Review verdict at eb94f83: CLEAN. Independently reproduced the partial-June-12 ancestor-island failure against the 2,980-event dataset, audited all channel cache writers/cursor transitions, and verified the event-carried frontier invariants. Review found and this head closes: content-only frontier selection, no downgrade on late ancestor/thread responses, marked-island exclusion from dense-second keyset seeds, and auxiliary-event exclusion from those seeds. Focused pager regressions pass; combined #1473 + #1483 + #1478 desktop suite passes 1502/1502; combined typecheck and focused Biome checks pass. Minimalness 9/10, elegance 9/10, correctness 9/10. User confirmation across reload/channel switching remains required before merge per the freeze. (GitHub will not accept an approval because this agent resolves to the PR owner account.)
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Problem
Tyler's June 14 → June 9 scrollback skip in #buzz-bugs (reported in #buzz-gui-performance; screenshot shows June 12 mostly missing). Root-caused deterministically against the real 2,980-event dataset: ancestor-island cursor poisoning, on main long before #1473.
useLoadMissingAncestors(by-id) anduseThreadReplies(subtree) merge events days older than the contiguously loaded window into the channel cache — isolated "islands".runPageOlderPassanchored itsuntilcursor onbaseline[0].created_at, assuming contiguity. With a June 9 island in cache, the scroll-up fetch pages backward from June 9 — June 13/12/11/10 are never requested.Fix
Out-of-band state rides on the events themselves:
RelayEvent.nonContiguous(local-only) — set by the newmergeNonContiguousTimelineMessages, used by both out-of-band writers. Already-cached copies are never downgraded.oldestContiguousHistoryTimestamp— the oldest unmarked content event.Validation
runPageOlderPassagainst a relay double: red on the old anchor, green on the frontier anchor; plus island-healing and all-islands-fallback cases.pnpm checkclean;tsc --noEmitclean.Stacked on #1473 (
fix/timeline-cap-eviction); composes with #1478 (StrictMode-safe trim). Fixes the fetch-cursor bug; #1473/#1478 fix the eviction bugs.