Port V1's collage and slideshow InstantPage blocks into the V2 renderer
(previously grey-box placeholders).
- Collage: layoutCollage computes the mosaic (MosaicLayout, the grouped-message
engine) over inner image/video sizes and flattens it into existing top-level
.mediaImage/.mediaVideo items + a caption, so gallery / reveal-cost / registry
/ hidden-media all handle the cells with no collage-specific code. Right-edge
cells bleed 4pt for the bubble's rounded clip.
- Slideshow: a new .slideshow laid-out item + InstantPageV2SlideshowView, an
eager paged carousel (UIScrollView + PageControlNode) of InstantPageImageNode
pages, wired through frame/offsetBy/collectMedias/stableId/reuse/makeItemView
and the reveal-cost non-text list.
- Gallery transitions generalized onto InstantPageItemView via
instantPageTransitionNode(for:)/instantPageUpdateHiddenMedia(_:) (default
nil/no-op; explicit per-class witnesses on the 4 static media views, the
slideshow forwards to its live pages) so the multi-media slideshow can
participate alongside single-media views.
Docs: document both in docs/instantpage-richtext.md.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
