The "All" feed stuttered because every row appearing ran markSeen, which did a
disk save(), an O(n) contains over a @Query'd SeenStory array, and triggered a
full feed re-render on each insert. Now markSeen does an O(1) insert into a
non-observed reference Set, no per-row save (the container autosaves), and
SeenStory is no longer @Query'd by the view. cacheStories also does one fetch +
an in-memory index instead of a query per story.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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