The bottom row of the grid was often blank, at a scroll position the user
could sit at indefinitely. Two numbers decided when the loaded window follows
the view, they lived in different languages, and they disagreed.
The grid loaded three screenfuls and Rust held the window still until the
first visible cell was three quarters of the way through them. Three quarters
of three screenfuls is 2.25, and the view itself is one screenful tall — so
the bottom of the screen had already travelled a quarter of a screenful past
the last loaded cell before anything moved. Those rows are not in the model,
so nothing is drawn for them.
The same margin was wrong upward, and exactly so. The window is placed a
quarter of itself behind the view, and the margin then declared the view too
close to the top at precisely that distance: every single row scrolled upward
re-read the catalog, rebuilt all 360 cells and re-queried their badges and
ratings, and so did the row after it.
So the grid now reports what it shows — a screenful, counting the row the
scroll position has cut in half, which `visible-rows` alone undercounts and
which is exactly the row reported missing — and Rust owns the rest: four
screenfuls loaded, placed a quarter back, and moved once the view comes within
half a screenful of an edge of them. One decision in one place, and the test
now walks the view the length of the library and asserts the window covers it
at every step.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
dtourolleandClaude Opus 5
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