MediaCache::enforce_budget never evicts the original of the photo on screen (set_on_screen), but it still
counted it. A 64 MP original (Sony A7R VI: 9984×6656 linear float, 760 MiB) nearly fills the default cache
share (768 MiB) alone, so the loop evicted everything else instead: the photo's preview and thumbnail sources,
the rendered previews and the prefetched neighbours. Every edit at 1:1 (the whole-frame render and the
thumbnail), every zoom out and every step to the next photo then decoded the raw again.
The pinned original is now left out of what is compared with the budget. The rest still fits the share; the
original sits over it, as the first commit of this PR already allowed.
Co-Authored-By: Claude <noreply@anthropic.com>
