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/Services/API/InvidiousAPI.swift

@@ -763,7 +763,7 @@ private struct InvidiousAuthPlaylist: Decodable, Sendable {
             description: description,
             author: author.map { Author(id: "", name: $0) },
             videoCount: videoCount,
-            thumbnailURL: videos?.first?.videoThumbnails?.first?.thumbnailURL(baseURL: baseURL),
+            thumbnailURL: Thumbnail.reliableURL(for: videos?.first?.videoThumbnails?.first?.thumbnailURL(baseURL: baseURL)),
             videos: videos?.map { $0.toVideo(baseURL: baseURL) } ?? []
         )
     }
@@ -1551,7 +1551,7 @@ private struct InvidiousPlaylist: Decodable, Sendable {
             description: description,
             author: authorId.map { Author(id: $0, name: author ?? "") },
             videoCount: videoCount,
-            thumbnailURL: validVideos.first?.thumbnails.first?.url,
+            thumbnailURL: Thumbnail.reliableURL(for: validVideos.first?.thumbnails.first?.url),
             videos: validVideos
         )
     }
@@ -1683,7 +1683,7 @@ private struct InvidiousSearchPlaylist: Decodable, Sendable {
             title: title,
             author: authorId.map { Author(id: $0, name: author ?? "") },
             videoCount: videoCount,
-            thumbnailURL: thumbnailURL,
+            thumbnailURL: Thumbnail.reliableURL(for: thumbnailURL),
             videos: videos?.map { $0.toVideo(baseURL: baseURL) } ?? []
         )
     }

Yattee/Services/API/PipedAPI.swift

@@ -532,9 +532,7 @@ private struct PipedVideo: Decodable, Sendable {
             publishedText: uploadedDate,
             viewCount: views.map { Int($0) },
             likeCount: nil,
-            thumbnails: thumbnail.flatMap { URL(string: $0) }.map {
-                [Thumbnail(url: $0, quality: .high)]
-            } ?? [],
+            thumbnails: Thumbnail.fallbackChain(for: thumbnail.flatMap { URL(string: $0) }),
             isLive: duration == -1,
             isUpcoming: false,
             scheduledStartTime: nil
@@ -771,9 +769,7 @@ private struct PipedSearchItem: Decodable, Sendable {
             publishedText: uploadedDate,
             viewCount: views.map { Int($0) },
             likeCount: nil,
-            thumbnails: thumbnail.flatMap { URL(string: $0) }.map {
-                [Thumbnail(url: $0, quality: .high)]
-            } ?? [],
+            thumbnails: Thumbnail.fallbackChain(for: thumbnail.flatMap { URL(string: $0) }),
             isLive: duration == -1,
             isUpcoming: false,
             scheduledStartTime: nil

Yattee/Services/API/YatteeServerAPI.swift

@@ -1363,7 +1363,7 @@ private struct YatteePlaylist: Decodable, Sendable {
             description: description,
             author: authorId.map { Author(id: $0, name: author ?? "") },
             videoCount: videoCount,
-            thumbnailURL: validVideos.first?.thumbnails.first?.url,
+            thumbnailURL: Thumbnail.reliableURL(for: validVideos.first?.thumbnails.first?.url),
             videos: validVideos
         )
     }
@@ -1440,7 +1440,7 @@ private struct YatteeSearchPlaylist: Decodable, Sendable {
             title: title,
             author: authorId.map { Author(id: $0, name: author ?? "") },
             videoCount: videoCount,
-            thumbnailURL: thumbnailURL,
+            thumbnailURL: Thumbnail.reliableURL(for: thumbnailURL),
             videos: videos?.map { $0.toVideo() } ?? []
         )
     }

Yattee/Services/Downloads/DownloadManager+Assets.swift

@@ -346,12 +346,17 @@ extension DownloadManager {
             var thumbnailPath: String?
             var channelThumbnailPath: String?
 
-            // Download video thumbnail (best quality) - best-effort, ignore failures
+            // Download video thumbnail - best-effort, ignore failures. The stored URL
+            // is the best advertised variant (often maxresdefault, which 404s for
+            // older videos), so walk the quality chain until one succeeds.
             if let thumbnailURL = download.thumbnailURL {
-                thumbnailPath = await downloadThumbnail(
-                    from: thumbnailURL,
-                    filename: "\(videoID)_thumbnail.jpg"
-                )
+                for candidate in Thumbnail.fallbackChain(for: thumbnailURL) {
+                    thumbnailPath = await downloadThumbnail(
+                        from: candidate.url,
+                        filename: "\(videoID)_thumbnail.jpg"
+                    )
+                    if thumbnailPath != nil { break }
+                }
             }
 
             // Download channel thumbnail - best-effort, ignore failures

Yattee/Services/Player/PlayerService.swift

@@ -522,8 +522,10 @@ final class PlayerService {
                    let localThumbnailPath = download.localThumbnailPath {
                     localThumbnailURL = downloadManager.downloadsDirectory().appendingPathComponent(localThumbnailPath)
                 }
+                // Reliable (hqdefault) variant: artwork is a single fetch with no
+                // fallback, and the best advertised variant often 404s.
                 await nowPlayingService.loadArtwork(
-                    from: videoForNowPlaying.bestThumbnail?.url,
+                    from: videoForNowPlaying.reliableThumbnailURL,
                     localPath: localThumbnailURL
                 )
             }

Yattee/Services/RemoteControl/RemoteControlCoordinator.swift

@@ -466,7 +466,7 @@ final class RemoteControlCoordinator {
         networkService.updateAdvertisement(
             videoTitle: state.currentVideo?.title,
             channelName: state.currentVideo?.author.name,
-            thumbnailURL: state.currentVideo?.bestThumbnail?.url,
+            thumbnailURL: state.currentVideo?.reliableThumbnailURL,
             isPlaying: state.playbackState == .playing
         )
     }
@@ -494,7 +494,7 @@ final class RemoteControlCoordinator {
             videoID: state.currentVideo?.id.videoID,
             videoTitle: state.currentVideo?.title,
             channelName: state.currentVideo?.author.name,
-            thumbnailURL: state.currentVideo?.bestThumbnail?.url,
+            thumbnailURL: state.currentVideo?.reliableThumbnailURL,
             currentTime: state.currentTime,
             duration: state.duration,
             isPlaying: state.playbackState == .playing,

Yattee/Services/TopShelfSnapshotWriter.swift

@@ -100,7 +100,7 @@ private extension TopShelfSnapshotWriter {
             title: bookmark.title,
             authorName: bookmark.authorName,
             duration: bookmark.duration,
-            thumbnailURL: bookmark.thumbnailURLString,
+            thumbnailURL: reliableThumbnailURLString(bookmark.thumbnailURLString),
             deepLinkURL: deepLink,
             progressSeconds: nil
         )
@@ -118,7 +118,7 @@ private extension TopShelfSnapshotWriter {
             title: entry.title,
             authorName: entry.authorName,
             duration: entry.duration,
-            thumbnailURL: entry.thumbnailURLString,
+            thumbnailURL: reliableThumbnailURLString(entry.thumbnailURLString),
             deepLinkURL: deepLink,
             progressSeconds: entry.watchedSeconds
         )
@@ -190,8 +190,17 @@ private extension TopShelfSnapshotWriter {
         }
     }
 
+    /// The Top Shelf extension sets a single image URL with no failure fallback,
+    /// so rewrite to the always-available `hqdefault` variant: the best advertised
+    /// variant is often `maxresdefault`, which 404s for many older videos and
+    /// would leave an empty tile.
     static func bestThumbnailURL(from thumbnails: [Thumbnail]) -> String? {
-        thumbnails.max(by: { $0.quality < $1.quality })?.url.absoluteString
+        Thumbnail.reliableURL(for: thumbnails.max(by: { $0.quality < $1.quality })?.url)?.absoluteString
+    }
+
+    static func reliableThumbnailURLString(_ urlString: String?) -> String? {
+        guard let urlString else { return nil }
+        return Thumbnail.reliableURL(for: URL(string: urlString))?.absoluteString ?? urlString
     }
 }
 #endif