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Warm a fence's highlighting like a parse, and page the restore by rows

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Two things the measurements for the previous commit turned up.

Highlighting a fence cost 174ms for a two-hundred-line Kotlin block, and
the lazy list charged it again every time that block scrolled back into
composition -- six times in one bench run, with the scroll's draw phase at
1.29ms per frame. So it is warmed and cached where parses already are:
`highlight` is a plain function taking no colour from the theme, `warm`
fills `ParsedReplies.highlighted` from `fences(parse)` off the drawing
thread, and `fenceContent` extracts the code here rather than through the
library's composable, so the string warmed is the string drawn.

And the anchor restore asked for a span counted in events, which goes
negative when the anchor's row is the oldest half-row and was coerced to
one -- a request per delta, six hundred round trips walking one reply back
a word at a time with the spinner up. It asks for a page of rows now.

Clean pairs, fresh sessions each side, same gestures. Fence scroll
(transcript-bench.sh): draw phase 0.74ms per frame before highlighting
existed, 0.77ms after, no lexing in the window either side. Streaming
forty linked items (stream-bench.sh): 2412ms of reparsing before, 674ms
after; mean 5.0ms to 1.4ms, worst 8.9ms to 7.9ms. Bullet glyphs, fence
colours, the image links and the reference link checked on the emulator;
lint clean on AGP 9.4.0.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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irisandClaude Opus 5 committed 2026-09-03 18:50:29 -04:00
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TRANSCRIPT_RENDERING.md
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@@ -162,92 +162,153 @@ and are the reason several tempting simplifications were rejected.
## Session of 2026-09-03: the list above, worked through
Items 1-5 of the previous list are implemented and build; the AGP bump from
item 7 is in. What is *not* done is in "What is next" below, and the state
of each measurement is stated honestly here so nothing has to be re-derived.
Items 1-5 of the previous list are done and checked on the emulator, and so
is the AGP bump from item 7. Two things were found while measuring them: a
174ms stall this work introduced and then removed, and a restore bug that
predates it. Both are described below with their numbers.
**1. Styled markers per depth -- done, unverified on screen.**
`MarkdownListItem`'s `Marker` draws `•`, `◦`, `▪` by depth (cycling) in
`listMarkerColor` (Theme.kt, Lavender: the scheme's secondary accent, which
nothing else used, so it now means "structure"). Ordered numbers take the
same colour. Still to check on the emulator: that `◦` and `▪` are in the
system fonts rather than drawing as boxes -- the comment on `BULLETS` claims
they were checked, and that check is what the next session owes it.
**1. Styled markers per depth.** `MarkdownListItem`'s `Marker` draws `•`,
`◦`, `▪` by depth, cycling past the third, in `listMarkerColor` (Theme.kt,
Lavender -- the scheme's secondary accent, which nothing else used, so it
now means "structure"). Ordered numbers take the same colour. All three
glyphs were checked on screen at four depths: they render from the system
fonts, no missing-glyph boxes. The colour is the same at every depth on
purpose -- depth is said by the glyph and the indent, and a colour per depth
would make a difference in degree look like one in kind.
**2. Syntax highlighting inside fences -- done, measured before only.**
`CodeFence.kt` holds `highlighted` (moved out of `ToolInput.kt`, timed as
`code highlighted`), the `fenceLanguage` alias table (extension or name to
the highlights lexer; unknown words stay plain on purpose), and `CodeFence`
/ `CodeBlock`, registered as the component table's `codeFence`/`codeBlock`.
The library's `MarkdownCodeFence` still finds the code inside the node; the
drawing is ours (same background, corner, padding and sideways scroll, minus
the shadow, border and empty pointer handler). Baseline `transcript-bench.sh`
on the fixture below, before the change: draw phase 0.72ms/frame, transcript
0.36ms, the 200-line kotlin fence one 10,700px block. The after run has not
been taken.
**2. Syntax highlighting inside fences.** `CodeFence.kt` holds it:
`highlight` (moved out of `ToolInput.kt`, so a reply's code and a tool
call's command are the same colours), the `fenceLanguage` alias table
(extension or name to the highlights lexer; a word not in it stays plain,
because a fence coloured by the wrong language's rules looks highlighted and
is wrong in a way the reader cannot see), `fenceContent`, and the
`codeFence`/`codeBlock` entries of the component table.
The measurement is the reason there is a cache. Highlighted naively, with
the answer held by a `remember` inside the fence, a two-hundred-line Kotlin
fence cost **174ms to lex** and the lazy list charged it again every time
the block scrolled back into composition -- six times in one bench run,
1043ms of lexing, and the scroll's draw phase up at 1.29ms per frame. So
highlighting is now warmed and cached exactly as parsing is
(`ParsedReplies.highlighted`, filled by `warm` from `fences(parse)`), and
`highlight` is a plain function taking no colour from the theme, which is
what lets it run off the drawing thread.
Because the warming has to ask for the same string the drawing does,
`fenceContent` extracts the code and the language word itself -- the rule
copied from the library's `MarkdownCodeFence`, which is a composable and so
cannot be called from `warm`. Two extractions would be two keys, and the
warmed answer would be missed at every fence with nothing saying so.
Clean pair, two fresh sessions of the same 200-line Kotlin fence, no saved
anchor, same gestures (`transcript-bench.sh`):
| | before (no highlighting) | after (warmed) |
|---|---|---|
| draw phase per frame | 0.74ms | 0.77ms |
| the transcript's share | 0.33ms | 0.33ms |
| lexing during the scroll | none | none |
**3. `MarkdownRoot` no longer calls the library's `Markdown()`.** It
provides the eight locals itself (`LocalReferenceLinkHandler` from the
parse, padding, dimens, colours, typography, a no-op image transformer,
animations, components).
provides the locals itself -- reference links from the parse, padding,
dimens, colours, typography, a no-op image transformer, animations,
components. Nothing between a piece and the screen is the library's now
except the leaf composables named in the component table.
**4. Paragraphs with images -- done differently from the plan.** The plan
said draw the image as its own piece; the app has no image loader and the
renderer's transformer was the no-op one, so an image in a reply drew as
*nothing*. An `IMAGE` node is now appended by `appendPlainLink` as a link
carrying its alt text (the address when there is none), and with no image to
place the `hasImage` branch and the renderer's `MarkdownText` are gone:
every paragraph is the platform `BasicText`.
said draw the image as its own piece; measuring first showed the app has no
image loader and the renderer's transformer was the no-op one, so an image
in a reply drew as *nothing at all*. An `IMAGE` node is now appended by
`appendPlainLink` as a link carrying its alt text (the address when there is
none), which says what was there and opens it. With no image to place, the
`hasImage` branch and the renderer's `MarkdownText` are gone: every
paragraph is the platform `BasicText`.
**5. Per-item units for a streaming list -- done, before measured, after
not.** `LiveParse.advanceTo` cuts at the last item of a multi-item list
(`openPiece`), provided that item has content beyond its marker (a bare `-`
may still become a paragraph line); the cut is at the start of the item's
line so indentation survives the reparse. `Segment.continues` marks a tail
that carries on a list, and `MarkdownPiece`'s `continuesList`/`listContinues`
keep the padding of an inner item at the seam so nothing moves when it
does. Measured with the new `app/stream-bench.sh` streaming
`/tmp/longlist.md` (forty bullet items with a link each) on the old build:
`markdown reparsed while streaming: 483, 3.9ms mean, 11.6ms worst`,
`record: one block` worst 1.6ms. The same run on the new build printed an
empty report -- the first thing to look at (the screen showed the list
drawn with `•` markers, so the build runs; the report tap or the idle wait
may have misfired).
**5. Per-item units for a streaming list.** `LiveParse.advanceTo` now cuts
at the last item of a multi-item list (`openPiece`), provided that item has
content beyond its marker -- a bare `-` is an empty item now and the first
character of a paragraph line once `-x` arrives, so cutting on it would draw
that line as a new item. The cut is at the start of the item's line, so the
indentation the reparse reads its nesting from survives.
`Segment.continues` marks a tail that carries on a list, and
`MarkdownPiece`'s `continuesList`/`listContinues` keep an inner item's
padding at the seam, so nothing moves when the seam does.
Clean pair, two fresh sessions, forty linked bullet items streamed word at a
time (`stream-bench.sh /tmp/longlist.md`):
| | before | after |
|---|---|---|
| reparses while streaming | 482 | 483 |
| total time in them | 2412ms | 674ms |
| mean / worst | 5.0ms / 8.9ms | 1.4ms / 7.9ms |
| `record: one block` worst | 1.8ms | 0.7ms |
The worst case moves least, which is the shape to expect: the first reparse
of a tail still covers whatever has arrived, and the last item can be long.
What changes is that every reparse after it covers one item instead of the
whole list.
**The restore walked back one event per request.** Found while benching, and
older than this work. `savedAnchor`'s loop asked for
`oldestSeq - anchor.seq + RESTORE_PAGE_CUSHION` events; when the anchor's row
is already loaded but is the oldest half-row (which `anchorRow` refuses,
correctly -- it grows when the page behind it lands), that span is negative
and was coerced to 1. So the restore fetched one event, then one more, at a
round trip each: six hundred requests walking a long reply back a word at a
time, with the screen on its spinner the whole way and the sandbox log
printing `limit=1` once a second. It now asks for a page counted in rows,
which is the only kind that can promise to reach the row behind the anchor.
**Harness.** `app/stream-bench.sh [-k] FILE` is `transcript-bench.sh` for a
reply still arriving: opens the first session, resets the report, sends
FILE through `ui-sandbox.sh send`, waits for idle, prints the report.
Fixtures used this session, all in `/tmp` (regenerate from the shapes
named): `fixture.md` (lists three deep, ordered and nested, fences in
reply still arriving: opens the first session, taps the app's own "Jump to
latest" so the list is pinned to the newest end, resets the report, sends
FILE, waits for the transcript to stop growing, prints the report. Both of
those last two are corrections to a first version that measured nothing:
a transcript parked further back never redraws while a reply streams into it
(the list must not move under a reader), and a session is idle at *both*
ends of a turn, so polling for idle answers before the turn has started.
Fixtures live in `/tmp` and are regenerated from the shapes named here:
`fixture.md` (lists four deep, ordered and nested, fences in
kotlin/rust/sh/none, a table with a link, a quote with a list, an inline and
a standalone image, a reference link), `longfence.md` (200-line kotlin
fence), `longlist.md` (40 linked items), `numlist.md`.
a standalone image, a reference link), `longfence.md` (200-line Kotlin
fence), `longlist.md` (40 linked items).
**Seen and not chased: a reconnect loop.** On the *old* build, restarting
the app onto the fixture session with a saved anchor mid-transcript while a
600-delta reply was streaming left the screen on a spinner, reconnecting
every 1.5s (`RECONNECT_DELAY_MS`) with `session screen recomposed: 26` and
the fence message re-warmed each time, until the sandbox server was
restarted. `events?after=N` more than `CATCH_UP_LIMIT` (200) behind answers
`reset` plus the newest 200 *raw* deltas, i.e. a window starting
mid-message; the restore loop and that reset clearing `items` look like the
two halves. Reproduce with `stream-bench.sh` (restart form) after a
`transcript-bench.sh` run has left an anchor mid-fence.
**Two traps in the emulator loop**, both of which cost a bench run here.
`adb shell pm clear` removes the enrolment and the notification permission
along with the saved anchors, so the next run measures a permission dialog;
re-enrol with the command `ui-sandbox.sh` prints and
`pm grant … POST_NOTIFICATIONS`. And a saved anchor is per session id, so
the only way two builds start a scroll from the same place is a *fresh
session for each*.
## What is next, in order
1. **Look at the fixture on the emulator** (session `fixture2` in the
sandbox holds only `fixture.md`): bullet glyphs at three depths, fence
colours, the image drawn as a link, the reference link at the foot.
2. **Take the after measurements**: `transcript-bench.sh` for the fence,
`stream-bench.sh /tmp/longlist.md` for the list, and put both pairs in
the commit message. Find out why the after run's report was empty.
3. **Lint** (`./gradlew :androidApp:lint`) on AGP 9.4.0; the bump is in
`libs.versions.toml` and the build passed, lint has not been run.
4. **The reconnect loop above.**
5. **File the highlights range bug upstream** -- no `gh` in this VM and no
GitHub credential, so it needs Bryan or a token. One-line repro: lexing
`x '*/a/*'` as `SyntaxLanguage.SHELL` in highlights 1.1.0 returns a
highlight whose `location.end` precedes its `location.start`.
6. Everything from the earlier list that still stands: regression runs
before and after any change to these files, pasted into the commit.
1. **A fence still arriving is lexed per delta.** `warm` covers settled
messages; the live tail's fence is highlighted on the composing thread by
`ParsedReplies.highlighted`'s inline miss, once per delta, and at 174ms
for a long one that is the stall above wearing a different hat. The tail
is short while it is being written, so this may already be cheap -- but
it is unmeasured, and `stream-bench.sh /tmp/longfence.md` is the run that
says. Cheapest fix if it bites: highlight the live tail only when it is
under some length, or move the miss off-thread the way `LiveParse` moved
parsing, keeping the plain text until the answer lands.
2. **The reconnect loop.** Restarting the app onto a session with a saved
anchor while a long reply was streaming left it reconnecting every 1.5s
(`RECONNECT_DELAY_MS`), spinner up, until the server was restarted.
`events?after=N` more than `CATCH_UP_LIMIT` (200) behind answers `reset`
plus the newest 200 *raw* deltas -- a window starting mid-message -- and
the reset clears `items`, which is the state the restore loop then pages
against. The one-event-per-request bug above was part of what made it so
visible; whether it survives that fix is the first thing to find out.
3. **File the highlights range bug upstream.** There is no `gh` and no
GitHub credential in this VM, so it needs Bryan or a token. One-line
repro: lexing `x '*/a/*'` as `SyntaxLanguage.SHELL` in highlights 1.1.0
returns a highlight whose `location.end` precedes its `location.start`.
Until then `highlight` drops such spans, which is why the shell fence in
`fixture.md` -- whose command contains `'*/.git/*'` -- draws plain while
an ordinary shell fence colours.
4. **Regression runs.** `transcript-bench.sh` and `stream-bench.sh` before
and after any change to the files above, with the report in the commit.
The numbers to watch are the worst `record: one block`, the reparse mean
while streaming, and the draw phase's accounting line.