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+# Stray pause at an episode transition (open investigation)
+
+> **Status:** Open. Root cause **not** confirmed — blocked on logs from both sides while it
+> happens. Everything below marked *verified* was read from the code; everything marked
+> *hypothesis* was not observed yet. Do not "fix" this from the hypotheses alone.
+>
+> Reported: 2026-08-15, against v3.1.0. Affected platform supports episode auto-sync
+> (parseable `SxxEyy` titles) — title *parsing* is explicitly **not** the problem here.
+
+---
+
+## Symptom
+
+Two peers watch a series together. At the end of an episode, one of them moves on to the
+next episode while the other stays **paused at the end of the previous one** and never
+recovers. Happens intermittently, not on every transition.
+
+## Reported sequence
+
+1. Peer A finishes episode 1, the player advances to episode 2.
+2. A detects the transition, opens an episode lobby and pauses itself in episode 2,
+   waiting for the others.
+3. Peer B is still a few seconds from the end of episode **1**.
+4. B receives a `PAUSE` and applies it — although that pause originates from a peer that
+   is already on episode 2, so it should have been discarded.
+5. B is now paused before its own transition, so its player never auto-advances, so B
+   never reports ready. A's lobby runs into the 60 s timeout and is cancelled.
+   From then on A and B are on different episodes and the guard (correctly) blocks
+   everything, so nothing recovers.
+
+## What the code does today (verified)
+
+**The episode guard already exists and already runs before anything is applied.**
+[`content.js:1197-1213`](../extension/content.js) is the first thing in the
+`SERVER_COMMAND` branch (after the host-control desync check). It compares the sender's
+title from the payload against the local title and skips `PLAY`/`PAUSE`/`SEEK`/
+`FORCE_SYNC_*` on mismatch.
+
+**The title is already shipped with every content-script command.** `sendContentEvent`
+attaches `mediaTitle` to play/pause/seek ([`content.js:1450-1469`](../extension/content.js)),
+and `routeToContent` forwards the payload to the content script unchanged
+([`background.js:2576`](../extension/background.js)). *Adding* the title to these events is
+therefore not an available fix — it is already there.
+
+**The guard is permissive by design.** `isDifferentEpisode`
+([`content.js:897-903`](../extension/content.js)) returns `false` — i.e. "allow" — when
+either side has no title or no parseable episode ID. This is deliberate: Netflix exposes
+no media title at all, JkAnime none, Disney+ only the series name (see
+[TESTED_SERVICES.md](TESTED_SERVICES.md)). Making the comparison mandatory would silently
+break sync on those platforms.
+
+**Titles come from `navigator.mediaSession.metadata`**
+([`content.js:863`](../extension/content.js)) — a page-level signal that is *not* coupled
+to what the `<video>` element is actually playing. It can lead, lag, or be briefly `null`
+across a source swap.
+
+**Self-inflicted pauses are suppressed by a 300 ms timer, not by a latch.**
+`_setSuppress` ([`content.js:65-70`](../extension/content.js)) self-clears after 300 ms.
+If the native `pause` event arrives later than that, the event is relayed as a normal user
+pause ([`content.js:1514-1517`](../extension/content.js)). The lobby pause
+(`PAUSE_FOR_LOBBY`, [`content.js:1291-1303`](../extension/content.js)) is issued exactly
+when the player is busy loading the next episode.
+
+**There is no `ended` listener.** Only `play`/`pause`/`seeked`/`loadeddata`/`waiting` are
+attached ([`content.js:1695`](../extension/content.js)), so a pause at the end of an
+episode is indistinguishable from a user pause.
+
+**Nothing resumes anyone after a failed lobby.** `EPISODE_LOBBY_CANCEL` only stops the
+poll ([`content.js:1284`](../extension/content.js)); `cancelEpisodeLobby`
+([`background.js:1732`](../extension/background.js)) does not resume the initiator.
+
+## Why the guard can let the pause through (hypotheses)
+
+Given that both the label and the comparison exist, the pause can only be applied if one
+of these three inputs is wrong at that instant. **Which one is unknown.**
+
+**(a) The sender's label is empty.** Players commonly clear `mediaSession.metadata` and
+re-set it across a source swap. A leaked lobby pause emitted inside that window carries
+`mediaTitle: null` → guard allows.
+
+**(b) The receiver's label is ahead.** The page may switch its metadata to episode 2
+before the `<video>` element actually advances. Then both sides read "episode 2", agree,
+and the pause is applied while B's picture is still episode 1.
+
+**(c) The guard is off on the receiver.** It only runs when `_autoSyncEnabled` is true
+([`content.js:1203`](../extension/content.js)), which is cached from `storage.local`
+([`content.js:241-243`](../extension/content.js)) — **per device, never synced between
+peers**. If "Auto-Sync next Episode" is disabled on the peer that freezes, it swallows
+every cross-episode command. This is the cheapest one to check and explains the asymmetry
+without any timing argument.
+
+(a) and (b) share a root cause: episode identity is sampled from a page-global signal that
+is not tied to the element's content.
+
+## How to confirm (do this next)
+
+Reproduce, then collect the logs from **both** peers via the *Status* tab → *Copy Logs*,
+and line them up by timestamp. Relevant strings, verbatim from the code:
+
+| Log line | Emitted by | Meaning |
+|---|---|---|
+| `Episode transition detected: "…"` | [`content.js:933`](../extension/content.js) | that peer's player advanced |
+| `Episode lobby created: "…"` | [`background.js:3582`](../extension/background.js) | that peer became the lobby initiator |
+| `Episode lobby received: waiting for "…"` | [`content.js:1276`](../extension/content.js) | the other peer entered the lobby |
+| `Episode mismatch: sender="…" vs mine="…" — skipping …` | [`content.js:1207`](../extension/content.js) | the guard fired |
+| `Local episode ready: "…"` | [`background.js:3620`](../extension/background.js) | that peer reached the expected episode |
+| `Episode lobby cancelled: …` | [`background.js:1740`](../extension/background.js) | 60 s timeout ([`constants.js:90`](../extension/shared/constants.js)) |
+
+What to read off:
+
+- A `PAUSE` from the other peer on B's side **without** an accompanying `Episode mismatch`
+  line → the guard did not fire. The `sender="…"` value in a *neighbouring* mismatch line
+  (if any) shows what A's label looked like at that moment, which separates (a) from (b).
+- No `Episode mismatch` line **anywhere** in B's log for the whole session, while episodes
+  clearly diverged → suspect (c); verify the setting directly.
+- A `PAUSE` from `You` in A's log shortly **after** `Episode lobby created` → A's own lobby
+  pause leaked past the 300 ms suppression.
+
+## Fix plan once confirmed
+
+Ordered by risk. The guiding rule is **fail open**: no change may create a state where
+nothing syncs at all — that is worse than the current symptom.
+
+1. **Never relay a pause we caused ourselves.** Replace the 300 ms stopwatch in
+   `_setSuppress` with an explicit latch that is cleared when the expected native event
+   arrives (or when the lobby ends). A programmatic pause is not a user command,
+   regardless of how long the player takes to report it.
+2. **Latch the episode identity to the element.** Derive it at `loadeddata` / source change
+   ([`content.js:1733`](../extension/content.js)) and use the latched value both for
+   labelling outgoing commands and for the local side of the comparison, instead of a live
+   `mediaSession` read. Kills (a) and (b). The building blocks (`lastKnownMediaTitle`,
+   `lastVideoSrc`) already exist.
+3. **Resume after a failed lobby.** Remember that we paused *for* the lobby and undo it on
+   cancel, so a failed auto-sync degrades to "keep watching" instead of a silent freeze.
+4. **Close the remaining title-less paths** (hygiene, not the cause of this symptom):
+   popup play/pause send `payload: {}` ([`popup.js:2251`](../extension/popup.js)), and the
+   lobby's force-sync sends `{ targetTime: 0.0 }` without a title
+   ([`background.js:1794`](../extension/background.js)) — the latter means a force-sync
+   firing while a peer is still on the old episode seeks that peer to 0.0 of the **old**
+   episode.
+
+## Rejected approaches (and why)
+
+- **"Just send the title with the pause."** Already done for this event
+  ([`content.js:1458`](../extension/content.js)) — nothing to add.
+- **"Force the comparison / refuse commands without a title."** Breaks Netflix, JkAnime and
+  Disney+ outright, plus films whose titles differ per language or provider, plus the
+  `hidden` media-title privacy mode which strips the title by design
+  ([`title-privacy.js:31-40`](../extension/title-privacy.js)). A silent "nothing syncs any
+  more" is worse than the current bug.
+- **Pinning the title at event time *alone*.** Tempting, but it would make the failure
+  *deterministic* rather than fix it: the stray pause would then always carry the old
+  episode and always be applied. Only acceptable together with items 1 and 2.
+- **Automatically resuming a stranded peer.** Reaching into someone else's playback is the
+  kind of automation that is worse than the symptom when it misfires. Only reconsider if
+  items 1-3 prove insufficient.
+
+## Code map
+
+| Concern | Location |
+|---|---|
+| Episode ID parsing / comparison | [`episode-utils.js`](../extension/episode-utils.js) (synced into `content.js` at build time) |
+| Guard on incoming commands | [`content.js:1197-1213`](../extension/content.js) |
+| Outgoing event + title sampling | [`content.js:1450-1545`](../extension/content.js) |
+| Echo suppression | [`content.js:59-77`](../extension/content.js) |
+| Transition detection | [`content.js:904-946`](../extension/content.js) |
+| Lobby (content side) | [`content.js:947-1003`](../extension/content.js), [`content.js:1264-1303`](../extension/content.js) |
+| Lobby (background side) | [`background.js:1707-1838`](../extension/background.js), [`background.js:3498-3624`](../extension/background.js) |
+| Title privacy | [`title-privacy.js`](../extension/title-privacy.js) |