scripts: bridge-emulator.sh (host) + image prefetching

Perf work for the TV FPS complaint: every page that loads from the API
also warms Coil's disk/memory caches (video thumbnails at the same
480x270 the card renders, channel banners/avatars) so rows scroll
without popping in over the network. Prefetch keys match render keys
exactly so cache hits are guaranteed.

bridge-emulator.sh runs OUTSIDE the container on the emulator host:
boots jtubesc if needed (ADB_VENDOR_KEYS whitelists the host adb key),
installs/starts JTube TV and binds :5557 -> adbd 5601 so the container
and LAN can drive it. Run it once in your rutherford shell.

app/src/main/java/net/jeena/jtubetv/JTubeApp.kt

@@ -13,8 +13,11 @@ object AppGraph {
         private set
     lateinit var tokenStore: TokenStore
         private set
+    var appContext: android.content.Context? = null
+        private set
 
     fun init(context: Application) {
+        appContext = context
         tokenStore = TokenStore(context)
         repository = PeerTubeRepository(tokenStore, PeerTubeNetwork(tokenStore))
     }

app/src/main/java/net/jeena/jtubetv/ui/list/ImagePrefetcher.kt

@@ -0,0 +1,53 @@
+package net.jeena.jtubetv.ui.list
+
+import android.content.Context
+import coil.imageLoader
+import coil.request.ImageRequest
+import net.jeena.jtubetv.AppGraph
+import net.jeena.jtubetv.data.api.Avatar
+import net.jeena.jtubetv.data.api.VideoChannelDto
+import net.jeena.jtubetv.data.api.VideoDto
+
+/**
+ * Warms Coil's caches for images that are already loaded from the API but not yet
+ * visible further down a row/list, so they pop in instantly instead of popping in
+ * over the network while scrolling.
+ *
+ * Uses the same request shape (size) as the visible [VideoCard]/[ChannelCard]
+ * renderers so the memory cache keys match exactly.
+ */
+object ImagePrefetcher {
+
+    private val enqueued = HashSet<String>()
+
+    fun videoThumbnails(videos: List<VideoDto>, context: Context = AppGraph.appContext!!) {
+        for (video in videos) {
+            val path = video.thumbnailPath?.takeIf { it.isNotBlank() } ?: continue
+            enqueue(context, AppGraph.repository.absoluteUrl(path), 480, 270)
+        }
+    }
+
+    fun channelArt(channels: List<VideoChannelDto>, context: Context = AppGraph.appContext!!) {
+        for (channel in channels) {
+            val banner = channel.banners.maxByOrNull { it.width }
+            if (banner != null) enqueue(context, absolute(banner), 480, 270)
+            val avatar = channel.avatars.maxByOrNull { it.width }
+            if (avatar != null) enqueue(context, absolute(avatar), 80, 80)
+        }
+    }
+
+    private fun absolute(a: Avatar): String =
+        (a.fileUrl ?: a.path).let {
+            if (it.startsWith("http")) it
+            else (AppGraph.tokenStore.baseUrl ?: "") + (if (it.startsWith("/")) "" else "/") + it
+        }
+
+    private fun enqueue(context: Context, url: String, width: Int, height: Int) {
+        if (!enqueued.add(url)) return
+        val request = ImageRequest.Builder(context)
+            .data(url)
+            .size(width, height)
+            .build()
+        context.imageLoader.enqueue(request)
+    }
+}

app/src/main/java/net/jeena/jtubetv/ui/list/PagedListViewModel.kt

@@ -27,6 +27,9 @@ abstract class PagedListViewModel<T> : ViewModel() {
 
     protected abstract suspend fun fetch(start: Long, count: Int): Result<List<T>>
 
+    /** Warm image caches for just-loaded rows so later scrolls don't fetch from network. */
+    protected open fun onChunkLoaded(chunk: List<T>) {}
+
     fun loadMore(force: Boolean = false) {
         if (inFlight || (!force && exhausted)) return
         inFlight = true
@@ -39,6 +42,7 @@ abstract class PagedListViewModel<T> : ViewModel() {
                         exhausted = chunk.size < pageSize
                         items = items + chunk
                         loadingInitial = false
+                        onChunkLoaded(chunk)
                     },
                     onFailure = { e ->
                         if (items.isEmpty()) {

app/src/main/java/net/jeena/jtubetv/ui/list/VideoListViewModel.kt

@@ -30,6 +30,17 @@ class VideoListViewModel(
     val query = MutableStateFlow("")
     private var activeSearch: String? = null
 
+    override fun onChunkLoaded(chunk: List<VideoListItem>) {
+        ImagePrefetcher.videoThumbnails(
+            chunk.mapNotNull {
+                when (it) {
+                    is VideoListItem.Video -> it.video
+                    is VideoListItem.HistoryEntry -> it.history.video
+                }
+            }
+        )
+    }
+
     override suspend fun fetch(start: Long, count: Int): Result<List<VideoListItem>> {
         return when (val s = source) {
             is ListSource.LocalVideos ->

app/src/main/java/net/jeena/jtubetv/ui/screens/ChannelsScreen.kt

@@ -109,6 +109,7 @@ class ChannelsViewModel(private val store: TokenStore) : ViewModel() {
                 userChannels = (userChannels + mine).distinctBy { it.name to it.host }
                 localChannels = rest.filter { it.host == host }.sortedBy { it.displayName }
                 followedChannels = rest.filter { it.host != host }.sortedBy { it.displayName }
+                net.jeena.jtubetv.ui.list.ImagePrefetcher.channelArt(all)
             } catch (e: Exception) {
                 error = e.message ?: "Could not load channels"
             } finally {

app/src/main/java/net/jeena/jtubetv/ui/screens/HomeRows.kt

@@ -65,7 +65,9 @@ class HomeRowsViewModel(private val repository: PeerTubeRepository) : ViewModel(
 
     private fun fetchSubs() {
         viewModelScope.launch {
-            subItems = repository.subscriptionVideos(0, 12).getOrNull()?.data ?: emptyList()
+            val subs = repository.subscriptionVideos(0, 12).getOrNull()?.data ?: emptyList()
+            subItems = subs
+            net.jeena.jtubetv.ui.list.ImagePrefetcher.videoThumbnails(subs)
         }
     }
 
@@ -108,6 +110,7 @@ class HomeRowsViewModel(private val repository: PeerTubeRepository) : ViewModel(
             }.awaitAll()
             continueItems = items
             continueLoading = false
+            net.jeena.jtubetv.ui.list.ImagePrefetcher.videoThumbnails(items.map { it.video })
         }
     }
 
@@ -122,6 +125,10 @@ class HomeRowsViewModel(private val repository: PeerTubeRepository) : ViewModel(
 
 /** Paged "New videos" row content. */
 class RecentVideosViewModel(private val repository: PeerTubeRepository) : PagedListViewModel<VideoDto>() {
+    override fun onChunkLoaded(chunk: List<VideoDto>) {
+        net.jeena.jtubetv.ui.list.ImagePrefetcher.videoThumbnails(chunk)
+    }
+
     override suspend fun fetch(start: Long, count: Int): Result<List<VideoDto>> =
         repository.localVideos(start, count).map { it.data }