Two background fills start inside open() with no caller input, through the
shared pools (#45) at background priority, so on-demand work always preempts
them. Thumbnails: every file newest first until all are on disk, sharing the
pool with thumbnails.ensure. Originals: the pinned set — favorites, then the
latest-week window ending at the newest file — through the content pool. The
pinned set is the eviction predicate (#47): a pinned original is never evicted,
and a file that leaves the set (favorite removed, or window moved on a later
refresh) becomes an ordinary evictable original. Each refresh re-kicks the
fills to pick up new files and retry failures. Progress via open() onProgress
and status().
Model: opus-4-8
sneak