Holding every row alive turned two per-row callbacks from a cost paid by
whatever was on screen into a cost paid by everything ever loaded, which
is why loading one more page of history made the whole transcript lag
and each page after made it worse. Both fire for every registered node
on every layout pass:
- an `onGloballyPositioned` per row, kept so a tap could be told which
half of the row it landed in
- an `onGloballyPositioned` per clickable inside a row, for the same
reason, so a tool group paid several
Neither is needed. One gesture detector on the whole list records where
a touch went down in the content's own coordinates, and the row's own
start is added up from heights when somebody actually taps -- so the
transcript keeps a height per row, which changes when the row does, in
place of a position per row, which is wrong the moment anything scrolls.
Positions for the saved-scroll anchor come from the same sum, and the
anchor is applied once per layout from the content rather than once per
row.
The reply cap is gone at Iris's request; she wasn't seeing it and does
not want it for now. It was doing measurable work -- p50 rises from 16ms
to 20ms on the emulator with it removed -- so it is worth knowing where
to look if long history feels heavy.
That 4ms is the only figure here I trust. This emulator's own noise
between identical repeats is larger than the difference the callback
change makes (identical builds measured 3.5% and 9.3% of frames over
budget), and its p50 of 16ms is already past a 120Hz budget, so it
cannot rank any of this the way the phone will. The callbacks are gone
because they are O(rows) per frame by construction and the list no
longer bounds how many rows there are -- not because a number here says
so.
Checked on the emulator against a real 1,200-event transcript: tapping a
collapsed row expands it with its top edge held exactly still, and a
scroll position comes back pixel-identical after leaving the session and
returning.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
irisandClaude Opus 5
f22c96abe2