fix(overlay): poll cheap playback state in the open subtitle sidebar (#290)

src/types/runtime.ts

@@ -55,6 +55,7 @@ import type {
   SubtitleData,
   SubtitleMiningContext,
   SubtitlePosition,
+  SubtitleSidebarPlaybackState,
   SubtitleSidebarSnapshot,
   SubtitleRendererStyleConfig,
   SubtitleStyleConfig,
@@ -477,6 +478,7 @@ export interface ElectronAPI {
   getCurrentSubtitleRaw: () => Promise<string>;
   getCurrentSubtitleAss: () => Promise<string>;
   getSubtitleSidebarSnapshot: () => Promise<SubtitleSidebarSnapshot>;
+  getSubtitleSidebarPlaybackState: () => Promise<SubtitleSidebarPlaybackState>;
   copySubtitleSidebarSelection: (text: string) => Promise<void>;
   getSubtitleSidebarOpen: () => Promise<boolean>;
   getPlaybackPaused: () => Promise<boolean | null>;

src/types/subtitle.ts

@@ -226,15 +226,25 @@ export interface SubtitleData {
   endTime?: number | null;
 }
 
-export interface SubtitleSidebarSnapshot {
+/**
+ * Per-tick sidebar state, served from main's cached state without mpv round-trips. When
+ * `sourceKey` or `cuesRevision` differs from the last full snapshot's, the renderer fetches a
+ * new `SubtitleSidebarSnapshot`.
+ */
+export interface SubtitleSidebarPlaybackState {
   sourceKey: string | null;
-  cues: SubtitleCue[];
-  currentTimeSec?: number | null;
+  /** Bumps whenever main swaps in a different parsed cue array. */
+  cuesRevision: number;
+  currentTimeSec: number | null;
   currentSubtitle: {
     text: string;
     startTime: number | null;
     endTime: number | null;
   };
+}
+
+export interface SubtitleSidebarSnapshot extends SubtitleSidebarPlaybackState {
+  cues: SubtitleCue[];
   config: SubtitleSidebarSnapshotConfig;
 }