fix(Lightbox): a single photo's caption sits on the caption's backing

.changeset/lightbox-gallery-caption-row.md

@@ -0,0 +1,9 @@
+---
+'@astryxdesign/core': patch
+---
+
+[feat] A Lightbox gallery's caption sits in a band two lines tall under every photo, so the photo keeps one size and place from item to item. A photo with no caption keeps the band's space without its backing. A longer caption shows two lines, the second ending in an inline "more" link, which opens the whole caption over the photo. The whole caption is always the viewer's accessible description.
+
+The viewer is a media surface: its controls, caption and counter take the theme's dark surface tokens through `MediaTheme`. The caption is body `Text` whose lines start at one edge, "more" and "less" are `Link`'s button form in the caption's own type, and the band clears the screen's bottom edge and its safe area. A gallery's caption sits on a backing that keeps it at 4.5:1 over any photo. A tap that opens the viewer paints no focus ring on its first control, and paging from a focused "more" or "less" keeps focus in the viewer.
+
+@vjeux

.changeset/lightbox-gallery-paging.md

@@ -4,7 +4,7 @@
 
 [feat] A Lightbox gallery now pages the way the iOS Photos viewer does. On a phone or tablet, drag or flick between items: the row follows your finger, and the release lands on the next or previous item, one at most. A gap of 40 px separates the items while they move. A zoomed photo pans with your finger until it reaches its edge; a new drag from that edge moves to the next item. A photo you leave zoomed returns to its fitted size once the gallery rests. Under a finger, the previous and next buttons and the arrow keys slide to the item instead of swapping it in place.
 
-Each item's caption moves with its item, right under its photo. `onIndexChange` also reports a swipe.
+Each item's caption moves with its item, in a caption band the gallery's photos share. `onIndexChange` also reports a swipe.
 
 Lightbox now loads its touch code with it, as Toast and Slider do. Its import grows from 51.4 KB to 99.6 KB gzip with the zoom and paging beneath, mostly shared touch modules that a page loads once; Lightbox's own code adds 14.1 KB minified.
 

.changeset/lightbox-single-caption-backing.md

@@ -0,0 +1,7 @@
+---
+'@astryxdesign/core': patch
+---
+
+[fix] A single photo's caption in a `Lightbox` now shows as a gallery's does. It sits in the band at the bottom of the viewer, on the caption's backing, which keeps 4.5:1 over any page behind it. The photo centres above it. A caption longer than two lines ends in "more", which opens it in full over the photo. A single photo with no caption shows no band.
+
+@vjeux

apps/storybook/stories/Lightbox.stories.tsx

@@ -128,7 +128,7 @@ export const WithZoom: Story = {
   },
 };
 
-/** Zoom on a photo with a caption, which sits under the fitted photo. */
+/** Zoom on a photo with a caption, in the caption band a gallery's pages use. */
 export const ZoomWithCaption: Story = {
   render: () => {
     const [isOpen, setIsOpen] = useState(false);
@@ -176,8 +176,9 @@ export const GalleryWithZoom: Story = {
 };
 
 /**
- * A gallery whose captions differ in length: the photo keeps one box
- * whichever pages, and so whichever captions, are rendered.
+ * A gallery whose captions differ in length. The first runs long, so two
+ * lines cut it short and "more" shows it all. The next runs about two lines,
+ * one has none, and the last is short. The photo keeps one box on every page.
  */
 export const GalleryWithCaptions: Story = {
   render: () => {
@@ -194,9 +195,13 @@ export const GalleryWithCaptions: Story = {
             {
               ...GALLERY_MEDIA[0],
               caption:
-                'A winding path through the forest, past the old mill and down to the river, where the trail turns back toward the village',
+                'A winding path through the forest, past the old mill and down to the river, where the trail turns back toward the village. In autumn the beeches along it turn copper, and on a clear morning you can see the church spire from the bridge before the path climbs the last hill home.',
+            },
+            {
+              ...GALLERY_MEDIA[1],
+              caption:
+                'Morning fog lifting off the lake, seen from the old stone bridge',
             },
-            GALLERY_MEDIA[1],
             GALLERY_MEDIA[3],
             {...GALLERY_MEDIA[2], caption: 'Golden hour'},
           ]}
@@ -233,6 +238,33 @@ export const GalleryKeepsIndex: Story = {
   },
 };
 
+/**
+ * A single photo whose caption runs long. As on a gallery's page, two lines
+ * cut it short and "more" shows it all.
+ */
+export const SingleWithLongCaption: Story = {
+  render: () => {
+    const [isOpen, setIsOpen] = useState(false);
+    return (
+      <>
+        <button onClick={() => setIsOpen(true)}>
+          Open single photo with a long caption
+        </button>
+        <Lightbox
+          isOpen={isOpen}
+          onOpenChange={setIsOpen}
+          media={{
+            ...GALLERY_MEDIA[0],
+            caption:
+              'A winding path through the forest, past the old mill and down to the river, where the trail turns back toward the village. In autumn the beeches along it turn copper, and on a clear morning you can see the church spire from the bridge before the path climbs the last hill home.',
+          }}
+          hasZoom
+        />
+      </>
+    );
+  },
+};
+
 export const WithCaption: Story = {
   render: () => {
     const [isOpen, setIsOpen] = useState(false);

docs/specs/AST-038-layer-text-boundary/spec.md

@@ -298,7 +298,7 @@ and ownership guards MUST remain component-owned when that equivalence is absent
 | [useLayer](../../../packages/core/src/Layer/useLayer.tsx) base typography                                                                              | Existing body family/size/leading are the one equivalent baseline moved into the private shared reset by the text-only implementation. No token/value or precedence change for those three declarations is intended.                                                                                              |
 | [Tooltip](../../../packages/core/src/Tooltip/useTooltip.tsx) painted surface                                                                           | Explicit body type, inverted colors, and content `wordBreak: break-word` are deliberate. Keep them; moving inner declarations outward can change supported overrides even where values match.                                                                                                                     |
 | [Toast](../../../packages/core/src/Toast/Toast.tsx)                                                                                                    | Uses body **defaults** for size/leading, surface inversion, and content `overflowWrap: anywhere`. This is not equivalent to replacing them with inherited live body variables. Keep them.                                                                                                                         |
-| [Lightbox](../../../packages/core/src/Lightbox/Lightbox.tsx), menu rows, keyboard hints, chart/radial tooltips                                         | Centered large captions, menu label/supporting type and start alignment, smaller nowrap keyboard hints, and compact chart wrapping remain intentional local presentation. Do not delete them as redundant resets.                                                                                                 |
+| [Lightbox](../../../packages/core/src/Lightbox/Lightbox.tsx), menu rows, keyboard hints, chart/radial tooltips                                         | Lightbox's caption renders through Text under MediaTheme (`component:Lightbox`). Menu label/supporting type and start alignment, smaller nowrap keyboard hints, and compact chart wrapping remain intentional local presentation. Do not delete them as redundant resets.                                         |
 | [useLayer portal writing context](../../../packages/core/src/Layer/useLayer.tsx), [padding reset](../../../packages/core/src/Layout/padding.stylex.ts) | Corrective portals preserve lost direction/writing mode without snapshotting tokens. The existing padding boundary resets its own structural variables. Preserve both; neither is a generic group or text barrier.                                                                                                |
 | Button/InputGroup end-cap rules and Collapsible/BottomSheetSwitcher context guards                                                                     | Already solve distinct membership/ownership problems. Preserve them; the text boundary does not replace sibling classification, nested presentation isolation, or sheet registration scope.                                                                                                                       |
 | `all: unset` on Item/TreeListItem/Collapsible/Stepper/Token/Thumbnail/ChatComposer controls                                                            | Local UA/control resets, not layer-root inheritance fixes. No new `all`/`unset`/`revert` layer reset is proposed. ToastViewport's `inset: unset` is geometry; menuWidth's `unset`/`revert` strings are caller-supplied width keywords routed to inline-size rather than `min()`, not a general inheritance reset. |