Three faults, all in how the outer bound behaved, and all of them mine.
**It was a destination.** Rows were stood up towards it a couple at a time
until the window was the full sixteen screens, whether or not anybody was
going to read them. Two rows is not a bounded amount of work -- a row here
runs to twenty-five screens of markdown -- so the transcript was laying
text out continuously in the background, and that is what the 70ms
measurements were. The bound is now a limit: the window grows because the
reader moved, and never speculatively. `standUpSome`, `growing` and the
frame loop that drove them are gone.
**It moved in two-screen steps**, which is the boundary that could be felt.
Crossing one moved the limit two screens at once and cut a chunk off the
trailing edge in a single frame; coming back the other way needed all of it
again, so oscillating around a boundary rebuilt the same rows repeatedly --
measured in the last report as twenty-two rows dropped and immediately
wanted back, which is also where the flicker was coming from. Recomputed
every time, the trailing edge retreats a row at a time and there is no
boundary left. The step existed because this used to be a scan of every
row; it has been a binary search since the last commit.
**It was measured against the viewport as it is now**, so the IME animation
shrank it on every one of its thirty frames -- trimming the far edge,
disposing rows and recomposing the list, thirty times, for a keyboard. How
much to keep alive is not a question the keyboard has any business
changing: it is about how far the reader might scroll, and they can scroll
just as far with it open. It is sized against the tallest the viewport has
been.
The bound also came down from eight screens to five. Eight was chosen when
keeping a row alive was believed to be free; the report now says plainly
that it is not -- three quarters of the draw phase is framework bookkeeping
that grows with live nodes rather than with what is on screen.
Measured on the emulator, eighty swipes oscillating across what used to be
a boundary: measurements of the transcript went from 51 at 8.3ms mean and
70.3ms worst to 11 at 2.3ms mean and 4.3ms worst, and rows composed from
270 to 10. Three keyboard cycles leave the transcript at 0.36ms of the
frame's draw phase. Three open/scroll/close cycles report nothing unbuilt.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
irisandClaude Opus 5
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