regenerate something when the sentences changed

ios/OralTrainer/Views/CatalogView.swift

@@ -45,6 +45,10 @@ final class CatalogViewModel: ObservableObject {
             do {
                 let document = try await SentenceBoundaryAPI.fetch(videoHash: video.videoHash)
                 boundaryDocuments[document.videoHash] = document
+                SentenceExplanationStore.shared.sync(
+                    mediaId: document.videoHash,
+                    sentences: document.sentences
+                )
                 updatedVideos[index] = video.copy(
                     durationMs: document.durationMs,
                     sentenceCount: document.sentences.count
@@ -75,6 +79,10 @@ final class CatalogViewModel: ObservableObject {
             return
         }
         if let document = boundaryDocuments[video.videoHash] {
+            SentenceExplanationStore.shared.sync(
+                mediaId: document.videoHash,
+                sentences: document.sentences
+            )
             let item = TrainingMediaItem(
                 id: video.videoHash,
                 title: video.title,
@@ -98,6 +106,10 @@ final class CatalogViewModel: ObservableObject {
                     return
                 }
                 boundaryDocuments[document.videoHash] = document
+                SentenceExplanationStore.shared.sync(
+                    mediaId: document.videoHash,
+                    sentences: document.sentences
+                )
                 controller.updateBoundaries(document.sentences)
                 controller.boundaryState = .loaded(count: document.sentences.count)
                 controller.showTransientMessage("课程已就绪：\(document.sentences.count) 句")
@@ -142,6 +154,10 @@ final class CatalogViewModel: ObservableObject {
                 guard activeVideoHash == hash else {
                     return
                 }
+                SentenceExplanationStore.shared.sync(
+                    mediaId: document.videoHash,
+                    sentences: document.sentences
+                )
                 controller.updateBoundaries(document.sentences)
                 controller.boundaryState = .loaded(count: document.sentences.count)
                 controller.showTransientMessage("句子边界已加载：\(document.sentences.count) 句")

ios/OralTrainer/Views/FullscreenPlayerView.swift

@@ -29,7 +29,8 @@ struct FullscreenPlayerView: View {
             SentenceExplanationSheet(
                 mediaId: controller.currentItem?.id ?? "",
                 courseTitle: controller.currentItem?.title ?? "口语训练课程",
-                sentence: sentence
+                sentence: sentence,
+                sentences: controller.currentItem?.sentences ?? []
             )
         }
     }

ios/OralTrainer/Views/PlayerSectionView.swift

@@ -27,7 +27,8 @@ struct PlayerSectionView: View {
             SentenceExplanationSheet(
                 mediaId: controller.currentItem?.id ?? "",
                 courseTitle: controller.currentItem?.title ?? "口语训练课程",
-                sentence: sentence
+                sentence: sentence,
+                sentences: controller.currentItem?.sentences ?? []
             )
         }
     }
@@ -273,6 +274,7 @@ struct SentenceExplanationSheet: View {
     let mediaId: String
     let courseTitle: String
     let sentence: SentenceBoundary
+    var sentences: [SentenceBoundary] = []
 
     @Environment(\.dismiss) private var dismiss
     @State private var explanation = ""
@@ -327,6 +329,7 @@ struct SentenceExplanationSheet: View {
             }
         }
         .task {
+            SentenceExplanationStore.shared.sync(mediaId: mediaId, sentences: sentences)
             if let cached = SentenceExplanationStore.shared.load(
                 mediaId: mediaId,
                 sentenceIndex: sentence.index