Hold the full painted backdrop until incoming hero art is ready

data/tv-spec/spec.md

@@ -73,7 +73,7 @@ Home heroes and shelves, Library rows, Discover hero/lanes, title headers, episo
 | Horizontal / vertical focus-follow scroll | 160 ms ease / 180 ms ease-out | Existing scroll geometry |
 | Discover pager | 180 ms, ease-out, retargeting current width and opacity | Buttons and pager remain outside the copy transition; reduced motion snaps width and caps opacity fades at 80 ms |
 
-Row reveals are grouped rather than the browser prototype's per-card staging: the armv7 frame budget permits one animated layer per shelf, not one per card. Tabs have no full-screen transition layer. The upper Home hero blend is bounded to **1920×820 px**, Discover to **1920×740 px**; the lower backdrop changes without an animated screen-sized layer. Hero copy is a separate bounded block with stationary action controls. Ordinary image reveal uses Coil's painter; hero-controlled requests bypass that independent fade so only the token-backed hero blend owns the transition. Existing poster-only blur is static.
+Row reveals are grouped rather than the browser prototype's per-card staging: the armv7 frame budget permits one animated layer per shelf, not one per card. Tabs have no full-screen transition layer. The upper Home hero blend is bounded to **1920×820 px**, Discover to **1920×740 px**; the entire painted backdrop stays static while incoming artwork loads, and the lower backdrop changes only when artwork or its final fallback is ready, without an animated screen-sized layer. Hero copy is a separate bounded block with stationary action controls. Ordinary image reveal uses Coil's painter; hero-controlled requests bypass that independent fade so only the token-backed hero blend owns the transition. Existing poster-only blur is static.
 
 The title page's scroll dim is a draw-only colour overlay, not an alpha-animated full-screen layer. Discover scrolls its backdrop through placement offsets rather than a full-screen translation layer. Initial loading animated layers are Home **2**, Library **up to 3** lazy rows, Discover **2**, title header **1**, person **2**; pending title episode/cast shelves add **1 each**, and each pending Discover lane owns **1**. Deep Home loading is bounded to **4** visible shelf layers. These are animated layers, not independent pulse clocks or every static display-list node: one shared pulse clock drives the loading screen without adding a layer. An ordinary hero hand-off animates **3** bounded owners (outgoing art and two copy blocks) above an opaque artwork base. Interruptions retain the painted composite without resetting alpha; each outgoing owner keeps its own original 320 ms artwork / 200 ms copy lifetime rather than restarting with later presses. Focus changes can animate **2** card transforms, **1** caption and at most **2** rating plates; ordinary artwork fades are painter draws without additional compositing layers. Late title metadata adds at most **4** bounded alpha layers: title ratings, play-target ratings, genres and overview. No animated owner is full-screen.
 

wolfskin-design/src/main/java/org/justinvisser/wolfskin/design/HeroMotion.kt

@@ -78,7 +78,7 @@ fun <T> HeroArtCrossfade(identity: Any, target: T, height: Dp, modifier: Modifie
         layers.forEach { if (it !== selected) it.outgoing = true }
     }
     Box(modifier) {
-        layers.forEachIndexed { index, layer -> key(layer) {
+        layers.forEach { layer -> key(layer) {
             SideEffect { if (layer.identity == identity) layer.target = target }
             LaunchedEffect(layer.outgoing, reduced) {
                 if (layer.outgoing) {
@@ -86,7 +86,7 @@ fun <T> HeroArtCrossfade(identity: Any, target: T, height: Dp, modifier: Modifie
                     layers.remove(layer)
                 }
             }
-            val outgoing = index != 0
+            val outgoing = layer.outgoing
             val onReady = remember(layer) { { layer.ready = true } }
             val bounds = if (outgoing) Modifier.requiredSize(WolfskinTokens.Shell.stageWidth, height) else Modifier
             Box(bounds.graphicsLayer { alpha = layer.alpha.value; clip = outgoing }

wolfskin-design/src/test/java/org/justinvisser/wolfskin/design/DiscoverHeroSequenceTest.kt

@@ -46,6 +46,7 @@ class DiscoverHeroSequenceTest {
     private val artAvailable = mutableStateOf(true)
     private val reduced = mutableStateOf(false)
     private var previousPixel: Int? = null
+    private var lowerPixel = 0
     private var largestJump = 0
     private var previousLayers = emptyMap<String, Pair<Float, Float>>()
     private val previousDotWidths = mutableMapOf<Int, Float>()
@@ -99,9 +100,14 @@ class DiscoverHeroSequenceTest {
         launch("slow")
         sample("settled", 0)
         val original = previousPixel
+        val originalLower = lowerPixel
         rule.runOnIdle { artAvailable.value = false }
         press(Key.DirectionRight)
-        frames("pending", 24)
+        repeat(24) { frame ->
+            rule.mainClock.advanceTimeBy(16)
+            sample("pending", frame)
+            assertEquals("Pending art cannot expose a placeholder beneath the hero", originalLower, lowerPixel)
+        }
         assertEquals("Pending art must not replace the painted backdrop", original, previousPixel)
         assertEquals(state.heroes.first().key, copyIdentities().single())
         rule.runOnIdle { artAvailable.value = true }
@@ -169,7 +175,10 @@ class DiscoverHeroSequenceTest {
         val file = File(directory, "$phase-${index.toString().padStart(2, '0')}.png")
         rule.onRoot().captureRoboImage(file.absolutePath)
         val bitmap = BitmapFactory.decodeFile(file.absolutePath)
-        val pixel = try { bitmap.getPixel(1600, 200) } finally { bitmap.recycle() }
+        val pixel = try {
+            lowerPixel = bitmap.getPixel(1600, 800)
+            bitmap.getPixel(1600, 200)
+        } finally { bitmap.recycle() }
         val channels = channels(pixel)
         previousPixel?.let { old -> largestJump = maxOf(largestJump, channels.zip(channels(old)).maxOf { (a, b) -> kotlin.math.abs(a - b) }) }
         previousPixel = pixel
@@ -197,7 +206,7 @@ class DiscoverHeroSequenceTest {
         } }
         previousSelection = state.slide
         samples.put(JSONObject().put("phase", phase).put("frame", index).put("timeMs", rule.mainClock.currentTime)
-            .put("selection", state.slide).put("rgb", JSONArray(channels)).put("copy", copy).put("layers", layers).put("dots", dots).put("navFocused", shell.navFocused))
+            .put("selection", state.slide).put("rgb", JSONArray(channels)).put("lowerRgb", JSONArray(channels(lowerPixel))).put("copy", copy).put("layers", layers).put("dots", dots).put("navFocused", shell.navFocused))
     }
 
     private fun layerSamples(): JSONArray {

wolfskin-design/src/test/java/org/justinvisser/wolfskin/design/HeroMotionTest.kt

@@ -62,16 +62,22 @@ class HeroMotionTest {
             val probe = BitmapFactory.decodeFile(probeFile.absolutePath)
             try {
                 for (y in listOf(380, 400, 420, 600, 800)) {
-                    assertEquals("The outgoing hero must stop at its 400px boundary: y=$y",
+                    assertEquals("Pending artwork cannot replace any part of the painted backdrop: y=$y",
-                        (if (y < 400) Color.Red else Color.Blue).toArgb(), probe.getPixel(100, y))
+                        Color.Red.toArgb(), probe.getPixel(100, y))
                 }
-                assertEquals(400f, rule.onNodeWithTag("hero-outgoing").fetchSemanticsNode().boundsInRoot.height, .01f)
             } finally { probe.recycle() }
             update { ready.value = true }
             rule.mainClock.advanceTimeBy(176)
             val mixed = pixel(directory, 100)
             assertNotEquals(Color.Red.toArgb(), mixed)
             assertNotEquals(Color.Blue.toArgb(), mixed)
+            val blendedProbe = BitmapFactory.decodeFile(probeFile.absolutePath)
+            try {
+                assertEquals("Only the outgoing blend is clipped at its 400px boundary",
+                    400f, rule.onNodeWithTag("hero-outgoing").fetchSemanticsNode().boundsInRoot.height, .01f)
+                assertEquals(Color.Blue.toArgb(), blendedProbe.getPixel(100, 400))
+                assertEquals(Color.Blue.toArgb(), blendedProbe.getPixel(100, 800))
+            } finally { blendedProbe.recycle() }
             rule.mainClock.advanceTimeBy(400)
             assertEquals(Color.Blue.toArgb(), pixel(directory, 100))
             update { selected.value = "green"; ready.value = false }