Prefetch artwork prev/next navigation off the critical path.

Move neighbor lookup into a dedicated service and let the viewer load adjacent artworks after first paint instead of blocking the detail request.

resources/js/lib/useNavContext.js

@@ -8,6 +8,22 @@ import { useCallback } from 'react';
 // Module-level cache for API calls
 const fallbackCache = new Map();
 
+function normalizeNavigation(data) {
+  if (!data || typeof data !== 'object') return null;
+  const hasPrev = data.prev_id == null || (data.prev_url && data.prev_slug);
+  const hasNext = data.next_id == null || (data.next_url && data.next_slug);
+  if (!hasPrev || !hasNext) return null;
+
+  return {
+    prevId: data.prev_id ?? null,
+    nextId: data.next_id ?? null,
+    prevUrl: data.prev_url ?? null,
+    nextUrl: data.next_url ?? null,
+    prevPreview: data.prev_preview ?? null,
+    nextPreview: data.next_preview ?? null,
+  };
+}
+
 async function fetchFallback(artworkId) {
   const key = String(artworkId);
   if (fallbackCache.has(key)) return fallbackCache.get(key);
@@ -16,28 +32,25 @@ async function fetchFallback(artworkId) {
     const res = await fetch(`/api/artworks/navigation/${artworkId}`, {
       headers: { Accept: 'application/json' },
     });
-    if (!res.ok) return { prevId: null, nextId: null, prevUrl: null, nextUrl: null };
+    if (!res.ok) return { prevId: null, nextId: null, prevUrl: null, nextUrl: null, prevPreview: null, nextPreview: null };
     const data = await res.json();
-    const result = {
-      prevId: data.prev_id ?? null,
-      nextId: data.next_id ?? null,
-      prevUrl: data.prev_url ?? null,
-      nextUrl: data.next_url ?? null,
-    };
+    const result = normalizeNavigation(data) || { prevId: null, nextId: null, prevUrl: null, nextUrl: null, prevPreview: null, nextPreview: null };
     fallbackCache.set(key, result);
     return result;
   } catch {
-    return { prevId: null, nextId: null, prevUrl: null, nextUrl: null };
+    return { prevId: null, nextId: null, prevUrl: null, nextUrl: null, prevPreview: null, nextPreview: null };
   }
 }
 
-export function useNavContext(currentArtworkId) {
+export function useNavContext(currentArtworkId, embeddedNavigation = null) {
   /**
    * Always resolve via API to guarantee same-user navigation.
    */
   const getNeighbors = useCallback(async () => {
+    const embedded = normalizeNavigation(embeddedNavigation);
+    if (embedded) return embedded;
     return fetchFallback(currentArtworkId);
-  }, [currentArtworkId]);
+  }, [currentArtworkId, embeddedNavigation]);
 
   return { getNeighbors };
 }