The card face's in-place expansion (03-board-ui.md § Card face): a card
with attachments, as the sole selection, grows a paged media band below
its title; every other state stays compact behind the quiet paperclip.
- CardCarousel owns the pure rules: the sole-selection predicate decides
by identity (a sole-selected lane matches no face, no snapshot walk),
and expansion is suppressed outside the animation key while a rubber
band is active — a band names a set in progress, so carousels neither
flicker nor animate under it.
- QuickLook thumbnails generate off-main into a per-window cache keyed to
survive reselection, with the Finder-icon fallback while loading and
for non-previewable types; pages ride the platform paging behavior,
dots (glass underlay, solid under Reduce Transparency) click to page,
and a local wheel monitor turns a discrete tick into one clamped page —
precise trackpad pans fall through untouched.
- The expansion animates under Motion's new carouselExpansion transaction
keyed narrowly on the sole-selected card; Reduce Motion goes instant.
Drop-slot math and the marquee read the expanded height for free — both
re-register on every size change.
928 unit tests (24 new). m5-interactions complete.
Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY
