Track the active chapter in PlayerState instead of per-tick time reads

Chapter lists highlighted the active row by reading currentTime in the
view body, re-rendering every row many times per second during
playback. PlayerState now stores a change-guarded activeChapterID
updated when time or chapters change, so views observe only chapter
transitions.

Yattee/Services/Player/PlayerState.swift

@@ -226,7 +226,9 @@ final class PlayerState {
     // MARK: - Time & Progress
 
     /// Current playback time in seconds.
-    var currentTime: TimeInterval = 0
+    var currentTime: TimeInterval = 0 {
+        didSet { updateActiveChapter() }
+    }
 
     /// Total duration in seconds.
     var duration: TimeInterval = 0
@@ -356,11 +358,27 @@ final class PlayerState {
     // MARK: - Chapters
 
     /// Video chapters if available.
-    var chapters: [VideoChapter] = []
+    var chapters: [VideoChapter] = [] {
+        didSet { updateActiveChapter() }
+    }
+
+    /// ID of the chapter containing the current playback time. Stored and
+    /// change-guarded so views highlighting the active chapter observe only
+    /// chapter transitions, not every time-pos tick — reading `currentTime`
+    /// from a panel body re-renders it many times per second during playback.
+    private(set) var activeChapterID: UUID?
 
     /// Current chapter based on playback time.
     var currentChapter: VideoChapter? {
-        chapters.last { $0.startTime <= currentTime }
+        guard let activeChapterID else { return nil }
+        return chapters.first { $0.id == activeChapterID }
+    }
+
+    private func updateActiveChapter() {
+        let id = chapters.last { $0.startTime <= currentTime }?.id
+        if activeChapterID != id {
+            activeChapterID = id
+        }
     }
 
     // MARK: - Storyboards

Yattee/Views/Player/Panels/ChaptersPanelPage.swift

@@ -19,7 +19,6 @@ struct ChaptersPanelPage: View {
     private var playerState: PlayerState? { playerService?.state }
 
     private var chapters: [VideoChapter] { playerState?.chapters ?? [] }
-    private var currentTime: TimeInterval { playerState?.currentTime ?? 0 }
     private var storyboard: Storyboard? { playerState?.preferredStoryboard }
 
     var body: some View {
@@ -50,9 +49,8 @@ struct ChaptersPanelPage: View {
     }
 
     private func isChapterActive(_ chapter: VideoChapter) -> Bool {
-        let nextChapter = chapters.first { $0.startTime > chapter.startTime }
-        let endTime = nextChapter?.startTime ?? .infinity
-        return currentTime >= chapter.startTime && currentTime < endTime
+        // Observes only chapter transitions, not per-tick currentTime updates.
+        playerState?.activeChapterID == chapter.id
     }
 
     private func preloadChapterSheets() async {

Yattee/Views/Player/Panels/InfoPanelPage.swift

@@ -230,7 +230,6 @@ struct InfoPanelPage: View {
     // MARK: - Inline Sections (prototype)
 
     private var chapters: [VideoChapter] { playerState?.chapters ?? [] }
-    private var currentTime: TimeInterval { playerState?.currentTime ?? 0 }
     private var storyboard: Storyboard? { playerState?.preferredStoryboard }
     private var relatedVideos: [Video] { video.relatedVideos ?? [] }
 
@@ -308,9 +307,8 @@ struct InfoPanelPage: View {
     }
 
     private func isChapterActive(_ chapter: VideoChapter) -> Bool {
-        let nextChapter = chapters.first { $0.startTime > chapter.startTime }
-        let endTime = nextChapter?.startTime ?? .infinity
-        return currentTime >= chapter.startTime && currentTime < endTime
+        // Observes only chapter transitions, not per-tick currentTime updates.
+        playerState?.activeChapterID == chapter.id
     }
 
     private func preloadChapterSheets() async {

Yattee/Views/Player/tvOS/TVDetailsPanelPages.swift

@@ -92,7 +92,6 @@ struct TVChaptersPanelList: View {
     private var playerState: PlayerState? { playerService?.state }
 
     private var chapters: [VideoChapter] { playerState?.chapters ?? [] }
-    private var currentTime: TimeInterval { playerState?.currentTime ?? 0 }
 
     var body: some View {
         ScrollViewReader { proxy in
@@ -124,9 +123,8 @@ struct TVChaptersPanelList: View {
     }
 
     private func isChapterActive(_ chapter: VideoChapter) -> Bool {
-        let nextChapter = chapters.first { $0.startTime > chapter.startTime }
-        let endTime = nextChapter?.startTime ?? .infinity
-        return currentTime >= chapter.startTime && currentTime < endTime
+        // Observes only chapter transitions, not per-tick currentTime updates.
+        playerState?.activeChapterID == chapter.id
     }
 }