fix(overlay): prevent secondary subtitle duplication

- Reject decimal subtitle track IDs
- Preserve repeated short dialogue lines

src/core/services/mpv-protocol.test.ts

@@ -181,6 +181,18 @@ test('dispatchMpvProtocolMessage emits subtitle track changes', async () => {
   ]);
 });
 
+test('dispatchMpvProtocolMessage rejects decimal subtitle track IDs', async () => {
+  const { deps, state } = createDeps();
+
+  await dispatchMpvProtocolMessage({ event: 'property-change', name: 'sid', data: '4.5' }, deps);
+  await dispatchMpvProtocolMessage(
+    { event: 'property-change', name: 'secondary-sid', data: '4.5' },
+    deps,
+  );
+
+  assert.deepEqual(state.events, [{ sid: null }, { sid: null }]);
+});
+
 test('dispatchMpvProtocolMessage enforces sub-visibility hidden when overlay suppression is enabled', async () => {
   const { deps, state } = createDeps({
     isVisibleOverlayVisible: () => true,

src/core/services/mpv-protocol.ts

@@ -283,7 +283,7 @@ export async function dispatchMpvProtocolMessage(
           : typeof msg.data === 'string'
             ? Number(msg.data)
             : null;
-      deps.emitSubtitleTrackChange({ sid: sid !== null && Number.isFinite(sid) ? sid : null });
+      deps.emitSubtitleTrackChange({ sid: sid !== null && Number.isInteger(sid) ? sid : null });
     } else if (msg.name === 'secondary-sid') {
       const sid =
         typeof msg.data === 'number'
@@ -292,7 +292,7 @@ export async function dispatchMpvProtocolMessage(
             ? Number(msg.data)
             : null;
       deps.emitSecondarySubtitleTrackChange({
-        sid: sid !== null && Number.isFinite(sid) ? sid : null,
+        sid: sid !== null && Number.isInteger(sid) ? sid : null,
       });
     } else if (msg.name === 'secondary-sub-delay') {
       const delay =

src/renderer/subtitle-render.test.ts

@@ -1434,10 +1434,10 @@ test('prepareSecondarySubtitleLines collapses karaoke syllable spam into one ded
   assert.deepEqual(prepareSecondarySubtitleLines(karaoke), ['ya This no ma ups']);
 });
 
-test('prepareSecondarySubtitleLines collapses a short stack of repeated ASS layers', () => {
+test('prepareSecondarySubtitleLines preserves repeated short dialogue without layer metadata', () => {
-  const layeredSign = ['Your', 'Your', 'Your', 'Your', 'mosaic'].join('\\N');
+  const dialogue = ['Wait', 'Wait', 'Wait'];
 
-  assert.deepEqual(prepareSecondarySubtitleLines(layeredSign), ['Your mosaic']);
+  assert.deepEqual(prepareSecondarySubtitleLines(dialogue.join('\\N')), dialogue);
 });
 
 test('prepareSecondarySubtitleLines preserves short simultaneous dialogue without repeats', () => {

src/renderer/subtitle-render.ts

@@ -657,24 +657,12 @@ function renderPlainTextPreserveLineBreaks(root: ParentNode, text: string): void
 // hover-pause band into a full-screen trap.
 const KARAOKE_MIN_LINE_COUNT = 8;
 const KARAOKE_MAX_MEDIAN_LINE_LENGTH = 4;
-const LAYERED_REPEAT_MIN_LINE_COUNT = 4;
-const LAYERED_REPEAT_MIN_COUNT = 3;
 
 function isKaraokeLikeLineSet(lines: string[]): boolean {
+  if (lines.length < KARAOKE_MIN_LINE_COUNT) return false;
   const lengths = lines.map((line) => line.length).sort((a, b) => a - b);
   const median = lengths[Math.floor(lengths.length / 2)] ?? 0;
-  if (median > KARAOKE_MAX_MEDIAN_LINE_LENGTH) return false;
+  return median <= KARAOKE_MAX_MEDIAN_LINE_LENGTH;
-
-  if (lines.length >= KARAOKE_MIN_LINE_COUNT) return true;
-  if (lines.length < LAYERED_REPEAT_MIN_LINE_COUNT) return false;
-
-  const repeatCounts = new Map<string, number>();
-  for (const line of lines) {
-    const count = (repeatCounts.get(line) ?? 0) + 1;
-    if (count >= LAYERED_REPEAT_MIN_COUNT) return true;
-    repeatCounts.set(line, count);
-  }
-  return false;
 }
 
 export function prepareSecondarySubtitleLines(text: string): string[] {