Apply thumbnail fallback everywhere a single URL was rendered

The previous fix rebuilt the quality chain when converting persisted
models back to videos, but many consumers discarded it again by
rendering bestThumbnail (usually a maxresdefault.jpg that 404s for
older videos) as a single URL with no fallback.

Extract the retry logic from VideoThumbnailView into FallbackLazyImage
and use it at every in-app site that can iterate: player thumbnails
(mini bar, expanded sheet loaders, autoplay previews, tvOS audio-mode
artwork - previously a silent black screen), video info card and tvOS
header, and the tvOS playlist cover.

Sites that fetch or send exactly one URL are rewritten to the
always-available hqdefault variant via Thumbnail.reliableURL (exposed
as Video.reliableThumbnailURL): Now Playing artwork, Top Shelf
snapshots, remote control state, the frozen transition thumbnail,
blurred info background, navigation covers, and playlist covers
derived from a video's first thumbnail in Invidious/Yattee Server
responses.

Also invert RecentPlaylist's upgrade helper, which rewrote covers *to*
maxresdefault, walk the quality chain when caching download thumbnails
for offline artwork instead of giving up after one 404, and expand the
remaining single-thumbnail Piped conversions into full chains.

Yattee/Views/Player/ExpandedPlayerSheet+Autoplay.swift

@@ -44,8 +44,9 @@ extension ExpandedPlayerSheet {
 
         // Clear loaded image so next video gets fresh thumbnail
         displayedThumbnailImage = nil
-        // Immediately switch to next video's thumbnail to prevent old thumbnail flash
-        displayedThumbnailURL = nextQueuedVideo?.video.bestThumbnail?.url
+        // Immediately switch to next video's thumbnail to prevent old thumbnail flash.
+        // Reliable variant: the frozen URL is loaded without fallback.
+        displayedThumbnailURL = nextQueuedVideo?.video.reliableThumbnailURL
         isThumbnailFrozen = true
 
         Task {
@@ -200,7 +201,7 @@ extension ExpandedPlayerSheet {
     func videoPreviewCard(video: Video) -> some View {
         HStack(spacing: 12) {
             // Thumbnail
-            LazyImage(url: video.bestThumbnail?.url) { state in
+            FallbackLazyImage(urls: video.thumbnailURLsByQuality) { state in
                 if let image = state.image {
                     image
                         .resizable()

Yattee/Views/Player/ExpandedPlayerSheet+Layouts.swift

@@ -691,11 +691,11 @@ extension ExpandedPlayerSheet {
                     let isBufferReady = playerState?.isBufferReady ?? false
                     let isAudioOnly = playerState?.currentStream?.isAudioOnly == true
                     let showThumbnail = !info.hasBackend || !isFirstFrameReady || !isBufferReady || isAudioOnly
-                    // Use frozen URL during transition, otherwise current video's thumbnail
-                    let thumbnailURL = isThumbnailFrozen ? displayedThumbnailURL : video.bestThumbnail?.url
+                    // Use frozen URL during transition, otherwise current video's thumbnail chain
+                    let thumbnailURLs = isThumbnailFrozen ? [displayedThumbnailURL].compactMap { $0 } : video.thumbnailURLsByQuality
 
                     // Hidden loader - loads image into @State (invisible)
-                    LazyImage(url: thumbnailURL) { state in
+                    FallbackLazyImage(urls: thumbnailURLs) { state in
                         Color.clear
                             .onChange(of: state.image) { _, newImage in
                                 if let newImage { displayedThumbnailImage = newImage }
@@ -1353,11 +1353,11 @@ extension ExpandedPlayerSheet {
                         let isBufferReady = playerState?.isBufferReady ?? false
                         let isAudioOnly = playerState?.currentStream?.isAudioOnly == true
                         let showThumbnail = !info.hasBackend || !isFirstFrameReady || !isBufferReady || isAudioOnly
-                        // Use frozen URL during transition, otherwise current video's thumbnail
-                        let thumbnailURL = isThumbnailFrozen ? displayedThumbnailURL : video.bestThumbnail?.url
+                        // Use frozen URL during transition, otherwise current video's thumbnail chain
+                        let thumbnailURLs = isThumbnailFrozen ? [displayedThumbnailURL].compactMap { $0 } : video.thumbnailURLsByQuality
 
                         // Hidden loader - loads image into @State (invisible)
-                        LazyImage(url: thumbnailURL) { state in
+                        FallbackLazyImage(urls: thumbnailURLs) { state in
                             Color.clear
                                 .onChange(of: state.image) { _, newImage in
                                     if let newImage { displayedThumbnailImage = newImage }

Yattee/Views/Player/ExpandedPlayerSheet.swift

@@ -840,8 +840,10 @@ private struct PlayerEventHandlersModifier: ViewModifier {
 
         // Clear loaded image so new video gets fresh thumbnail
         displayedThumbnailImage = nil
-        // Capture thumbnail URL immediately and freeze to prevent flash during details load
-        displayedThumbnailURL = playerState?.currentVideo?.bestThumbnail?.url
+        // Capture thumbnail URL immediately and freeze to prevent flash during details load.
+        // Use the reliable (hqdefault) variant: the frozen URL is loaded without fallback,
+        // and the best advertised variant often 404s for older videos.
+        displayedThumbnailURL = playerState?.currentVideo?.reliableThumbnailURL
         isThumbnailFrozen = true
     }
 

Yattee/Views/Player/MiniPlayerView.swift

@@ -67,12 +67,11 @@ struct MiniPlayerView: View {
         return currentVideo?.title ?? String(localized: "player.notPlaying")
     }
 
-    /// The thumbnail URL to display, preferring DeArrow thumbnail if available.
-    private var displayThumbnailURL: URL? {
-        if let video = currentVideo, let deArrowThumbnail = deArrowProvider?.thumbnailURL(for: video) {
-            return deArrowThumbnail
-        }
-        return currentVideo?.bestThumbnail?.url
+    /// Thumbnail URLs to try in order, preferring DeArrow, then the quality chain.
+    private var displayThumbnailURLs: [URL] {
+        guard let video = currentVideo else { return [] }
+        let deArrowThumbnail = deArrowProvider?.thumbnailURL(for: video)
+        return [deArrowThumbnail].compactMap { $0 } + video.thumbnailURLsByQuality
     }
 
     // MARK: - Actions
@@ -406,7 +405,7 @@ struct MiniPlayerView: View {
 
     @ViewBuilder
     private var thumbnailView: some View {
-        LazyImage(url: displayThumbnailURL) { state in
+        FallbackLazyImage(urls: displayThumbnailURLs) { state in
             if let image = state.image {
                 image
                     .resizable()

Yattee/Views/Player/tvOS/TVAutoplayCountdownView.swift

@@ -62,7 +62,7 @@ struct TVAutoplayCountdownView: View {
     private var nextVideoCard: some View {
         HStack(spacing: 20) {
             // Thumbnail
-            LazyImage(url: nextVideo.video.bestThumbnail?.url) { state in
+            FallbackLazyImage(urls: nextVideo.video.thumbnailURLsByQuality) { state in
                 if let image = state.image {
                     image
                         .resizable()

Yattee/Views/Player/tvOS/TVPlayerView.swift

@@ -6,6 +6,7 @@
 //
 
 #if os(tvOS)
+import NukeUI
 import SwiftUI
 
 /// Focus targets for tvOS player controls navigation.
@@ -644,13 +645,15 @@ struct TVPlayerView: View {
             // Thumbnail for audio-only playback and the pre-backend loading state
             if isAudioOnly || !hasBackend,
                let video = playerState?.currentVideo,
-               let thumbnailURL = video.bestThumbnail?.url {
-                AsyncImage(url: thumbnailURL) { image in
-                    image
-                        .resizable()
-                        .aspectRatio(contentMode: .fit)
-                } placeholder: {
-                    Color.black
+               !video.thumbnailURLsByQuality.isEmpty {
+                FallbackLazyImage(urls: video.thumbnailURLsByQuality) { state in
+                    if let image = state.image {
+                        image
+                            .resizable()
+                            .aspectRatio(contentMode: .fit)
+                    } else {
+                        Color.black
+                    }
                 }
                 .allowsHitTesting(false)
             }