Follow-up to windowed particle pagination: adapt the stream UI now that the
loaded set is a window rather than the whole stream.
Progress indicator: drop the absolute "{n} / {total}" counter (the true count
is unknown when paginated) in favour of a streaming, count-free scrubber. It
renders a sliding window of segments around the current position (newest on
the right); the edge stubs page through the loaded window and pull in older
history via onLoadOlder when scrubbing past the oldest loaded segment.
Stream list sidebar: auto-fetch older particles via an IntersectionObserver
sentinel as the user scrolls toward the top, with viewport scroll-anchoring so
prepended history doesn't jolt the view. Auto-scroll-to-current is now gated on
genuine selection changes (not index shifts from prepends). Header count gains
a "+" while more history exists, and a spinner shows while paging.
ScrollArea gains an optional `viewportRef` to expose the scroll viewport for
anchoring and observers.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V8gsmdVd7R8PJtn4UFnC4J
Claude
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