frontend/src/components/discovery/MasonryGrid.vue

@@ -6,7 +6,6 @@
           v-for="item in col" :key="item.id"
           class="fc-masonry__item"
           :class="{ 'fc-masonry__item--anim': shouldAnimate(item) }"
-          :style="itemStyle(item)"
           type="button"
           @click="$emit('open', item.id)"
         >
@@ -66,12 +65,6 @@ function shouldAnimate(item) {
   return idx !== undefined && idx >= props.animateFromIndex
 }
 
-function itemStyle(item) {
-  if (!shouldAnimate(item)) return {}
-  const idx = idxById.value.get(item.id) - props.animateFromIndex
-  return { '--stagger-index': idx }
-}
-
 function aspectStyle(item) {
   const w = Number(item.width)
   const h = Number(item.height)
@@ -117,12 +110,15 @@ useInfiniteScroll(sentinelEl, () => {
 .fc-masonry__end { text-align: center; padding: 32px 0; }
 
 /* Cascade entry: each tile flips up out of a backward tilt and settles
-   into place, one at a time — more pronounced than a plain fade so the
-   showcase reads as an "experience" (operator-flagged 2026-05-28). The
-   `both` fill holds the hidden/tilted 0% state until each tile's staggered
-   turn; the cubic-bezier overshoots slightly past flat then settles.
-   Honors prefers-reduced-motion. Tunables: tilt (-28deg), stagger (70ms),
-   duration (0.6s). */
+   into place — more pronounced than a plain fade so the showcase reads as an
+   "experience" (operator-flagged 2026-05-28). The reveal is paced entirely by
+   the store, which pushes one fully-decoded item at a time (showcase.js); each
+   tile therefore animates the instant it mounts, with NO per-index CSS delay —
+   the old `animation-delay: index×70ms` compounded on top of the insert
+   cadence and made the cascade drag and desync as it grew (operator-flagged
+   2026-06-04). The `both` fill holds the hidden/tilted 0% state until mount;
+   the cubic-bezier overshoots slightly past flat then settles. Honors
+   prefers-reduced-motion. Tunables: tilt (-28deg), duration (0.6s). */
 @keyframes fc-masonry-item-in {
   0% {
     opacity: 0;
@@ -138,7 +134,6 @@ useInfiniteScroll(sentinelEl, () => {
   transform-origin: center top;
   backface-visibility: hidden;
   animation: fc-masonry-item-in 0.6s cubic-bezier(0.34, 1.45, 0.64, 1) both;
-  animation-delay: calc(var(--stagger-index, 0) * 70ms);
 }
 @media (prefers-reduced-motion: reduce) {
   .fc-masonry__item--anim {

frontend/src/stores/showcase.js

@@ -1,6 +1,7 @@
 import { defineStore } from 'pinia'
 import { ref, computed } from 'vue'
 import { useApi } from '../composables/useApi.js'
+import { preloadImage } from '../utils/preloadImage.js'
 
 // Buffered producer/consumer so the cascade cadence is decoupled from fetch
 // latency (operator-flagged 2026-06-04). The OLD pipeline trickled each batch
@@ -9,15 +10,21 @@ import { useApi } from '../composables/useApi.js'
 // sometimes-cold blocks; RTT jitter) the animation starved and the view
 // "burped" out a clump of images. Now:
 //   - PRODUCER (_fill): races ahead fetching batches into `queue` up to a
-//     target depth, refilling whenever the queue dips below BUFFER_MIN.
-//   - CONSUMER (_drain): pops ONE item every CADENCE_MS, independent of when
-//     fetches land. It only waits if the buffer genuinely starves.
-// As long as fetches keep up on average (a 3-row fetch is usually well under
-// the BUFFER_MIN×CADENCE runway), images appear at a perfectly even pace.
-// The very first image still waits on the first fetch (a cold TABLESAMPLE is a
-// separate, query-side concern); everything after it is buffer-smoothed.
+//     target depth, refilling whenever the queue dips below BUFFER_MIN. It
+//     also kicks off the image PRELOAD for each queued item so decoding
+//     pipelines ahead of the reveal.
+//   - CONSUMER (_drain): pops ONE item, WAITS for its thumbnail to be fully
+//     decoded, then reveals it — at most one per CADENCE_MS. Because the
+//     producer preloads ahead, the decode-wait is usually already satisfied,
+//     so the reveal stays evenly paced without idling the network.
+// The decode-gate is what makes the showcase's signature cascade land each
+// tile fully-loaded (the flip-in animates a real image, never a gray
+// placeholder); the single-item reveal keeps it strictly one-at-a-time
+// (operator-flagged 2026-06-04). The very first image still waits on the first
+// fetch + decode (a cold TABLESAMPLE is a separate, query-side concern);
+// everything after it is buffer-smoothed.
 const PAGE = 3
-const CADENCE_MS = 80          // ≈ the MasonryGrid 70ms stagger animation
+const CADENCE_MS = 80          // floor between fully-loaded reveals
 const PRIME = 6                // items buffered before the drain starts
 const BUFFER_TARGET = 30       // producer tops the queue up to this
 const BUFFER_MIN = 12          // ...and refills once the queue dips below this
@@ -42,12 +49,21 @@ export const useShowcaseStore = defineStore('showcase', () => {
   // Internal buffer (not reactive — the consumer is what feeds the UI via
   // images.value).
   let queue = []
+  // id -> Promise that settles when the thumbnail is paint-ready. Started by
+  // the producer so decoding runs ahead of the reveal; awaited by the consumer
+  // so no tile is shown before its image is loaded.
+  let _preloads = new Map()
   // Sequence token: shuffle / re-mount bumps it so in-flight producers and
   // the drain bail instead of interleaving two runs into one images list.
   let _seq = 0
   let _filling = false
   let _draining = false
 
+  function _preload(item) {
+    if (!_preloads.has(item.id)) _preloads.set(item.id, preloadImage(item.thumbnail_url))
+    return _preloads.get(item.id)
+  }
+
   // One batch, retried while the random sample comes back all-duplicates.
   // Returns the fresh items, or null when the API is genuinely empty.
   async function _fetchFresh(mySeq) {
@@ -79,6 +95,7 @@ export const useShowcaseStore = defineStore('showcase', () => {
         if (mySeq !== _seq) return
         if (batch === null) { exhausted.value = true; return }
         queue.push(...batch)
+        batch.forEach(_preload)  // pipeline decoding ahead of the reveal
       }
     } finally {
       _filling = false
@@ -104,7 +121,10 @@ export const useShowcaseStore = defineStore('showcase', () => {
         }
         if (mySeq !== _seq) return
         if (queue.length === 0) return  // exhausted + empty
-        images.value.push(queue.shift())
+        const item = queue.shift()
+        await _preload(item)  // reveal only once the thumbnail is fully decoded
+        if (mySeq !== _seq) return
+        images.value.push(item)
         await _sleep(CADENCE_MS)
       }
     } finally {
@@ -120,6 +140,7 @@ export const useShowcaseStore = defineStore('showcase', () => {
     const mySeq = _seq
     images.value = []
     queue = []
+    _preloads = new Map()
     seen.clear()
     exhausted.value = false
     error.value = null

frontend/src/utils/preloadImage.js

@@ -0,0 +1,21 @@
+// Resolve once the image at `url` is fully loaded AND decoded (paint-ready),
+// or after `timeoutMs` as a safety net so a broken/slow image never stalls a
+// cascade. Never rejects — the caller only cares that it's safe to reveal.
+//
+// Used by the showcase cascade to gate each tile's entry animation on the
+// thumbnail actually being ready, so the flip-in plays on a real image rather
+// than on a gray placeholder (operator-flagged 2026-06-04).
+export function preloadImage (url, timeoutMs = 4000) {
+  return new Promise((resolve) => {
+    let done = false
+    const finish = () => { if (!done) { done = true; resolve() } }
+    const img = new Image()
+    img.onload = finish
+    img.onerror = finish
+    img.src = url
+    // decode() resolves at paint-ready (a beat after onload); prefer it when
+    // available, but onload/onerror/timeout all still settle the promise.
+    if (typeof img.decode === 'function') img.decode().then(finish).catch(() => {})
+    setTimeout(finish, timeoutMs)
+  })
+}

frontend/test/showcase.spec.js

@@ -1,5 +1,13 @@
 import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest'
 import { setActivePinia, createPinia } from 'pinia'
+
+// Mock the decode-gate so the cascade is paced purely by the store's cadence
+// in tests (no real <img> load events in happy-dom). Individual tests can
+// override per-call to exercise the gating itself.
+vi.mock('../src/utils/preloadImage.js', () => ({
+  preloadImage: vi.fn(() => Promise.resolve()),
+}))
+import { preloadImage } from '../src/utils/preloadImage.js'
 import { useShowcaseStore } from '../src/stores/showcase.js'
 
 let nextId
@@ -25,6 +33,8 @@ describe('showcase store: buffered cascade', () => {
   beforeEach(() => {
     setActivePinia(createPinia())
     nextId = 1
+    preloadImage.mockReset()
+    preloadImage.mockImplementation(() => Promise.resolve())
     vi.useFakeTimers()
   })
   afterEach(() => {
@@ -60,6 +70,21 @@ describe('showcase store: buffered cascade', () => {
     expect(s.images.length).toBe(60)
   })
 
+  it('does not reveal a tile until its image has decoded', async () => {
+    stubShowcase()
+    let release
+    // The first tile's preload hangs until we release it; all others resolve.
+    preloadImage.mockImplementationOnce(() => new Promise((r) => { release = r }))
+    const s = useShowcaseStore()
+    const p = s.loadInitial()
+    await vi.advanceTimersByTimeAsync(1000)
+    expect(s.images.length).toBe(0)   // gated on the un-decoded first image
+    release()
+    await vi.advanceTimersByTimeAsync(6000)
+    await p
+    expect(s.images.length).toBe(60)  // cascade proceeds once it decodes
+  })
+
   it('flags an empty library without starting the cascade', async () => {
     stubShowcase({ empty: true })
     const s = useShowcaseStore()