Bryan's report after the last change read no worse in the numbers -- medians
unchanged, worst stall halved -- but scrolling felt bumpier while messages
loaded, and instrumenting the split paths found the feeling's likely source:
work the counters never saw.
The live reply's block split (BlockedMarkdown) recomputed on the composing
thread at every delta -- a whole-message parse of the growing text, 815 of
them and 2.9 seconds inside one streamed reply, a few milliseconds per delta
on the thread that draws, plus a cache entry per partial text that nothing
reads again. It now works the way parsedMarkdown already did one file over:
first split inline so the row has its height, every later one off-thread,
drawing one split behind, cached nowhere. Emulator, same streamed fixture:
anim p90 7.3 -> 3.4ms, p99 9.3 -> 4.7ms.
The settle moment had the same shape: nothing warms live deltas, so the
just-finished reply's split parse ran inside the flatten, uncounted, in a
frame. The flatten now splits a reply only when ParsedReplies.splitReady
says warm() has made its parses; the session screen warms the one cold row
off-thread and re-flattens (warmedTick), so the whole-to-blocks swap always
composes against ready parses. Readiness is an explicit mark set by warm()
rather than a peek into the blocks cache, because a message with memory
notes is warmed as its parts -- inferred readiness left it unsplittable
forever and re-warmed on every fold.
Also: user slices shrink to ~1000 chars (about one viewport, so a slice
composing mid-fling costs a few milliseconds, not sixty), and the split and
flatten paths are all timed -- "units flattened", "markdown split into
blocks", "message cut into parts", "user message cut into slices", "blocks
split while streaming" -- so the next "it feels bumpier" report names its
cause instead of hiding it in anim.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
irisandClaude Fable 5
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