Two adjacent swipe-time defects, one diagnosis each:
1. Height differed between current and neighbouring slides during a
swipe but matched when the arrow buttons advanced the carousel.
Cause: neighbour slides wrap their image in a div with extra `px-2`
horizontal padding while the current slide does not. `object-contain`
then sees a narrower container on neighbours, so wide images cap on
width first and render shorter than the same image at the current
position. Removed the padding so both slots share the same container
geometry. Arrow-button navigation looked fine because it never
showed the neighbour layout side-by-side.
2. The image flashed black for ~100–400 ms each time a swipe committed
to the next slide. Cause: the 3-slide track has no React keys, so
React reconciled slides by position. After commit the photo at every
position changed (`prev → current → next` shifts left), every slot's
`<AuthenticatedImage>` saw a new `src` prop, and its fetch effect
restarted from the placeholder state — including the slot that was
the user's "next" slide a moment ago and held a fully-loaded image.
Added a stable `key` derived from `photo.id` so React MOVES existing
DOM nodes across slots instead of refetching. 2-photo galleries are
a key-collision edge case (`prev === next`), so they fall back to
slot-prefixed keys to keep siblings unique; behaviour there is no
worse than today.
Paul Nothaft
d2d55098d6