fix(sync): harden episode transition compatibility

extension/episode-utils.js

@@ -4,6 +4,16 @@
  * Keep in sync with the injection block in content.js!
  */
 
+// The relay clamps episode titles to 100 UTF-16 code units. Clamp before the
+// wire and before strict comparison as well; otherwise a valid long local title
+// can never match the relay's authoritative value.
+export const EPISODE_WIRE_TITLE_LENGTH = 100;
+
+export function toEpisodeWireTitle(title) {
+    if (typeof title !== 'string' || title.length === 0) return null;
+    return title.substring(0, EPISODE_WIRE_TITLE_LENGTH);
+}
+
 export function extractEpisodeId(title) {
     if (!title || typeof title !== 'string') return null;
     const se = title.match(/S(?:eason\s*)?(\d+)[^a-zA-Z0-9]*E(?:pisode\s*)?(\d+)/i);
@@ -39,8 +49,64 @@ function episodeContext(title) {
 // it to agree so two unrelated S01E06 videos cannot cross-sync. Privacy-reduced
 // S/E-only titles still fall back to the canonical episode ID.
 export function sameEpisodeStrict(titleA, titleB) {
-    if (!sameEpisode(titleA, titleB)) return false;
-    const contextA = episodeContext(titleA);
-    const contextB = episodeContext(titleB);
-    return !contextA || !contextB || contextA === contextB;
+    const wireTitleA = toEpisodeWireTitle(titleA);
+    const wireTitleB = toEpisodeWireTitle(titleB);
+    if (!sameEpisode(wireTitleA, wireTitleB)) return false;
+    const contextA = episodeContext(wireTitleA);
+    const contextB = episodeContext(wireTitleB);
+    if (!contextA || !contextB || contextA === contextB) return true;
+    // Players disagree about whether MediaSession.title contains the series,
+    // episode title, or both. Accept a complete token-boundary subset while
+    // still rejecting unrelated contextual titles for the same S/E number.
+    const [shorter, longer] = contextA.length <= contextB.length
+        ? [contextA, contextB]
+        : [contextB, contextA];
+    return shorter.length >= 4 && ` ${longer} `.includes(` ${shorter} `);
+}
+
+export function createEpisodeWireIdentity(title) {
+    const expectedEpisodeId = extractEpisodeId(title);
+    const expectedTitle = toEpisodeWireTitle(title);
+    if (!expectedTitle || !expectedEpisodeId) return null;
+    return { expectedTitle, expectedEpisodeId };
+}
+
+export function sameEpisodeIdentity(localTitle, expectedTitle, expectedEpisodeId = null) {
+    const normalizedExpectedId = typeof expectedEpisodeId === 'string'
+        ? expectedEpisodeId.trim().toUpperCase().substring(0, 16)
+        : null;
+    if (normalizedExpectedId && extractEpisodeId(localTitle) !== normalizedExpectedId) return false;
+    return sameEpisodeStrict(localTitle, expectedTitle);
+}
+
+export function createLocalEpisodeDeadline(remainingMs, fallbackMs, now = Date.now()) {
+    const safeFallback = Number.isFinite(fallbackMs) && fallbackMs > 0 ? fallbackMs : 0;
+    const safeRemaining = Number.isFinite(remainingMs)
+        ? Math.max(0, Math.min(safeFallback, remainingMs))
+        : safeFallback;
+    return {
+        remainingMs: safeRemaining,
+        deadlineAt: now + safeRemaining
+    };
+}
+
+export function isEpisodeSyncV2StartContextCurrent(pending, current, now = Date.now()) {
+    return !!pending
+        && !!current
+        && now - pending.requestedAt >= 0
+        && now - pending.requestedAt <= 15000
+        && pending.roomId === current.roomId
+        && pending.connectionGeneration === current.connectionGeneration
+        && pending.targetGeneration === current.targetGeneration
+        && pending.tabId === current.tabId;
+}
+
+export function matchesEpisodeSyncV2StartRejection(pending, current, rejection, now = Date.now()) {
+    if (!isEpisodeSyncV2StartContextCurrent(pending, current, now)) return false;
+    const rejectionTitle = toEpisodeWireTitle(rejection?.expectedTitle);
+    const rejectionEpisodeId = typeof rejection?.expectedEpisodeId === 'string'
+        ? rejection.expectedEpisodeId.trim().toUpperCase().substring(0, 16)
+        : extractEpisodeId(rejectionTitle);
+    return rejectionTitle === pending.expectedTitle
+        && (!rejectionEpisodeId || rejectionEpisodeId === pending.expectedEpisodeId);
 }