logan 3479ae8d39 feat(ui): warm album art ahead of the scroll ...

Scrolling the albums grid pops art in: the cards already draw the
smallest adequate tier and are already lazy, so what was left is *when*
the request happens. The grids are virtualized, so the `<img>` — and
therefore the fetch — does not exist until the virtualizer renders its
card, which is about 1000px past the viewport, or two screens on the
reference device.

The issue asks for a larger overscan and that is not available:
`_overhang` is a hard-coded `protected` field on `BaseLayout` with no
configuration surface. So the request is issued ahead of the element
instead. `utils/image-prefetch.ts` warms a bounded window either side
of the rendered range, from `rangeChanged` rather than
`visibilityChanged` — the two report different ranges, and a window
measured from what is *visible* is spent on cards that already exist.

Cover and artist URLs are served under `Cache-Control: immutable`
(content-hashed filenames), so a prefetched image is a cache hit by the
time its card is drawn. The bytes are the browser's; what this holds is
the set of URLs asked for, capped and reported to `__yjCacheStats()`.

Measured on the bulk seed (4 988 albums), ten 2 400px jumps, covers in
the viewport with `naturalWidth === 0`: 254 of 258 blank one frame
after the jump and 214 two frames after, against 117 and 77 with the
prefetch.

Closes #65

2026-08-25 13:55:43 -04:00

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