fix(showcase): don't exhaust on all-dupe batches; retry up to 8x

/api/showcase returns a random sample; after enough scrolling, an
unlucky 3-item batch can be entirely in the `seen` Set, which was
flipping `exhausted=true` and surfacing "End." mid-scroll. The
showcase is endless by intent — only a genuinely empty API response
(library has 0 images) should mark it exhausted. Tiny-library
fallback: cap retries at 8 to avoid spinning forever.

frontend/src/stores/showcase.js

@@ -19,6 +19,16 @@ import { useApi } from '../composables/useApi.js'
 const PAGE = 3
 const INITIAL_BATCHES = 20
 const APPEND_DELAY_MS = 80  // ≈ the MasonryGrid stagger animation (70 ms)
+// Operator-flagged 2026-06-01: scrolling the showcase eventually hit a
+// premature "End." because /api/showcase returns a *random sample* and
+// after enough scrolling the `seen` Set accumulated enough to fully
+// collide with a 3-item batch. The showcase is supposed to be endless;
+// only a genuinely empty API response (library has zero images) should
+// mark it exhausted. Retry up to FETCH_RETRY_CAP times on all-dupe
+// batches; only flip `exhausted` when the API returns 0 items OR every
+// retry came back dupe-only (graceful fallback for tiny libraries
+// where retries will keep returning the same handful of items).
+const FETCH_RETRY_CAP = 8
 
 
 function _sleep(ms) { return new Promise(r => setTimeout(r, ms)) }
@@ -48,17 +58,32 @@ export const useShowcaseStore = defineStore('showcase', () => {
     }
   }
 
-  // Single batch — used by infinite-scroll appends. Trickles its 5 items
-  // in for the same one-at-a-time cadence as the initial load.
+  // Single batch — used by infinite-scroll appends. Trickles its items
+  // in for the same one-at-a-time cadence as the initial load. Retries
+  // up to FETCH_RETRY_CAP times when the API's random sample comes back
+  // all-duplicates (the showcase is endless by design; only a genuinely
+  // empty API response should mark it exhausted, not an unlucky sample).
   async function fetchPage() {
     if (loading.value) return
     loading.value = true
     error.value = null
     try {
-      const body = await api.get('/api/showcase', { params: { limit: PAGE } })
-      const fresh = (body.images || []).filter(i => !seen.has(i.id))
-      if (fresh.length === 0) { exhausted.value = true; return }
-      await _trickleAppend(fresh, _seq)
+      for (let attempt = 0; attempt < FETCH_RETRY_CAP; attempt++) {
+        const body = await api.get('/api/showcase', { params: { limit: PAGE } })
+        const items = body.images || []
+        // API genuinely empty → library is empty / endpoint exhausted.
+        if (items.length === 0) { exhausted.value = true; return }
+        const fresh = items.filter(i => !seen.has(i.id))
+        if (fresh.length > 0) {
+          await _trickleAppend(fresh, _seq)
+          return
+        }
+        // All-dupes batch — keep trying. Showcase is endless by intent.
+      }
+      // Retry cap hit with zero fresh items: library is probably much
+      // smaller than the running `seen` set, fall back to exhausted so
+      // the UI stops trying. Operator can shuffle to reset `seen`.
+      exhausted.value = true
     } catch (e) {
       error.value = e.message || String(e)
     } finally {