[Archive] perf(message-scroller): transcript virtualization (A+B) — evaluated, deferred - #1318
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[Archive] perf(message-scroller): transcript virtualization (A+B) — evaluated, deferred#1318roxi3906 wants to merge 4 commits into
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… @tanstack/react-virtual
…ent estimates Streaming into a long transcript rebuilt per-row data with O(n) scans of conversationGraph.messages (graph node lookup, revisions collection) for every row on every 33ms presentation tick — O(rows^2) per tick. At 2000 rows this produced multi-hundred-ms long tasks per streamed chunk (p95 frame 134-172ms, 16 longtasks/~1.9s per stream). Hoist the scans into per-render indexes memoized on conversationGraph identity (graphMessageNodeById, graphRuntimeSegmentById, revisionMessagesByRootId, messageCreatedAtById, subsequentTurnCountByMessageId), making the row map O(1) per row. Also let MessageScrollerItem take a containmentEstimate and pass per-row-type contain-intrinsic-size values (user 3rem, agent 21rem, from measured row heights), cutting scrollHeight drift while offscreen rows resolve from ~8.5% to ~1%. Benchmark (2000 rows, streaming): frame p95 134-172 -> 66-68ms, longtasks 16 -> 5, longtask total ~1.9s -> ~0.5s; scroll and TTI unchanged. Adapted to the virtualized transcriptRows descriptor builder on this branch: the memoized graph indexes (graphMessageNodeById, graphRuntimeSegmentById, revisionMessagesByRootId) and the message maps are consumed inside the row-builder memo instead of the old inline render map, so the per-row O(n) graph scans are gone from the descriptor rebuild as well. containmentEstimate coexists with virtualization (applies to mounted rows only).
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Closing as archive-only: virtualization evaluated and deferred (see PR body for benchmark comparison and rationale). Branch retained on origin for reference. |
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Archived for reference — not intended for merge. Evaluation branch for transcript virtualization per the shadcn Message Scroller Virtualization recipe, combined with the indexing fix from #1210 (A+B).
Contents
ac2664f0— virtualize transcript rows past a 100-row threshold with@tanstack/react-virtual@3.14.9; app-side anchoring/follow-output engine replaces the primitive's MutationObserver-based behavior on the virtualized path.c07a45b1— cherry-pick of the per-row graph-lookup indexing fix from perf(message-scroller): transcript perf fixes + keep identity continuous across session bind #1210, adapted to consume the memoized indexes inside the virtualizedtranscriptRowsdescriptor builder.Benchmark (2000 messages, same protocol as #1210)
Why deferred
content-visibilityalready covers the 500–2000 row range; virtualization's streaming win only completes when combined with A.scrollToMessagereturns false for unmounted rows, and find-in-page / cross-range selection / accessibility tree cover only mounted rows.Verification (final combined build)
Perf spec 2 passed; message-scroll anchor/reanchor/release e2e 3 passed; 189 related unit tests pass unmodified; tsc (web+node) and eslint clean (one informational
react-hooks/incompatible-librarywarning foruseVirtualizer).