fix(player): give every transcode its own play session, and stop the one it replaces

Switching bitrate mid-film stalled playback. The server served the new
playlist and then rejected its segments: 400 on hls1/main/0.ts, six times
over 25 seconds, never recovering, while the UI logged "Streaming quality
changed" as if nothing were wrong.

Jellyfin keys a transcode job by device and play session. Every stream URL
this app built carried the same hardcoded DeviceId and no PlaySessionId at
all, so the second stream for an item was indistinguishable from the first
and nothing ever stopped the old ffmpeg. Re-opening a stream is not rare —
a quality switch, a transcoded seek and an audio-track switch all do it.
Replayed against the server, a second stream opened for a live job's item
alternates per attempt between serving bytes and 400ing, which is why it
read as flaky rather than broken.

begin_video_play_session mints a session id per open and reports the one it
supersedes; the URL builder stops that job (DELETE /Videos/ActiveEncodings,
un-retried — a slow stop must not delay playback) before returning. Putting
it in the builder rather than in each caller covers every re-open path by
construction. adopt_video_play_session takes ownership of the job the server
starts itself when PlaybackInfo answers with a TranscodingUrl: without it the
first switch on a stream has nothing to stop and collides with what is
playing.

Two client faults made the same incident worse and go with it:

- The fatal-HLS-error handler added the transcode seek offset to a position
  that already included it. Past roughly the halfway mark of a film the
  doubled value cleared the "near end" threshold, so any transient network
  error was reported as end-of-stream and autoplay skipped to the next item
  — precisely when a quality switch had just made the offset large. The
  decision now lives in hlsRecovery.ts, against the absolute position.
- The HTML5 reload primitive resolved on its own canplay timeout, so a
  reload the server never served reported success. The picker showed a
  quality that was not playing and the caller had nothing to revert.

TRACES: UR-074, UR-004 | DR-177 | UT-173, UT-174, UT-175

docs/requirements.md

@@ -334,11 +334,8 @@ Internal architecture, components, and application logic.
 | DR-162 | Video streams are opened against a **bandwidth ceiling the user chose**, instead of a fixed allowance nobody could change. Every video URL carried `MaxStreamingBitrate=20000000`/`VideoBitrate=18000000`, `PlaybackInfo` negotiated at 20 Mbps, and the device profile advertised `999999999` — so on a metered or slow connection the only lever was not watching. `StreamingQuality` is a ladder of ceilings (Original, 20/10/8/4/2/1 Mbps, 720 kbps) in which a step is not a label but a bundle of transcode parameters: the total ceiling, the audio share of it, and the resolution that budget can carry. It lives in Rust because those numbers are Jellyfin encoding vocabulary — the frontend names a variant and reads labels back over `player_get_streaming_qualities`, the same arrangement as the EQ preset curves. The video bitrate is the total *minus* the audio share, so the two together honour the cap rather than overshooting it by the size of the audio track, and `MaxHeight` falls with the ladder so a small budget is not spent on pixels it cannot afford. The cap has to reach the **negotiation**, not only the transcode URL: `max_static_bitrate` in the device profile is what makes the server refuse to direct-play a source fatter than the ceiling, and without it a 30 Mbps remux is handed over untouched and every URL parameter downstream is moot — which is why it is applied at all four places that decide bandwidth (the HLS builder, `PlaybackInfo`, `open_live_stream`, and the background-audio handoff, which takes the lower of the cap and its own 384 kbps). The ceiling is process-wide rather than a field on `OnlineRepository`, mirroring `INCLUDE_CATALOG_BROWSE`: it is a preference about *this device's connection*, it must survive a repository rebuilt on re-login, and every builder plus the negotiation have to agree on it or the cap leaks. Settings owns the durable default and is the only writer to `app_settings` — persisted unlike the rest of `VideoSettings`, because a limit set for a metered connection that silently reverts to uncapped on the next launch spends the user's data with no changed setting to show for it — and it is restored at startup from the async runtime, defaulting to uncapped if the read fails so a database problem degrades to the old behaviour rather than to an arbitrary limit. The in-player menu is the per-video override: a cap is a property of the stream the server is producing, so it cannot be applied to one already in flight — `player_set_stream_quality` re-opens the stream at the new quality and resumes at the current position, reloading a native backend itself and handing HTML5 a URL for the same `reloadSource` primitive the audio-track switch uses, so no strategy branch lives in the UI. It deliberately does not persist. This gives UR-070 its resume-at-the-same-point mechanism; the server-offered per-item rendition list that requirement also asks for remains proposed | Playback | UR-074, UR-070 | Done |
 | DR-174 | Tiles of mixed shapes are laid out **justified** rather than gridded. A CSS grid gives every cell one box, so on a page holding square music covers, 16:9 library backdrops and 2:3 posters at once, everything that is not the chosen shape is cropped to it — the home shortcut strip was explicitly forcing `aspect="video"` on music libraries for exactly this reason, which lined the row up by cutting the covers down. `layoutMosaic` packs tiles into rows of a **shared height** and gives each its own width from its own aspect ratio: it adds tiles to a row until the height needed to fill the container has fallen to the target, closes the row there (so rows land at or below the target, never above), and justifies the row to the container width by absorbing the rounding remainder into its widest tile, where a pixel is least visible. The last row is deliberately *not* justified — with one tile left over, filling the width would inflate it to a banner — so it sits at the target height, left-aligned. Ratios are clamped to a band, which costs a crop on genuine outliers and stops one panorama owning a row or one very tall image shrinking to a sliver. It is a pure module with no DOM: the component supplies only the two things the DOM knows — the measured container width, and the artwork's *decoded* aspect ratio, reported by `CachedImage` so the layout uses the shape an image actually has rather than the one its item type implies. Those measurements are committed in one debounced batch rather than per image, because artwork arrives over several hundred milliseconds and re-packing on each arrival would shuffle the grid under the pointer repeatedly. Labels are drawn *over* the bottom of each tile rather than beneath it: a caption below sits outside the computed box, and one that wraps to two lines would break the row alignment the layout exists to provide | UI | UR-075 | Done |
 | DR-175 | A library knows which favourites category it belongs to, and the frontend does not work it out. The mosaic offers a favourites tile per category beside its library, which needs a collection-type → category answer; deriving it in Svelte would have re-created the exact leak `SearchScope::item_types` was extracted to close (docs/specs/scoped-search-boundary.md) — one table of Jellyfin vocabulary, differing only in which vocabulary. `SearchScope::for_collection_type` maps `movies`/`tvshows`/`music` and returns `None` for everything else, so a Live TV or books library gets no tile at all rather than one opening an unfiltered list; `All` is never derived from a library, being the cross-library entry offered beside them rather than a property of one. `Library::new` stamps the result onto every library at construction — a constructor rather than a struct literal precisely so a derived field cannot be forgotten at one of the four sites — and it rides to the frontend as an optional `favoritesScope`, absent rather than null when there is none. The UI's remaining share is presentation only: what to call the tile, where to put it, and showing a category's tile **once** however many libraries share it, since two movie libraries have one favourites list between them | UI | UR-075, UR-067 | Done |
-| DR-176 | The server is never asked to burn a subtitle into the picture. `PlaybackInfo` omitted `SubtitleStreamIndex`, which does not mean "none" — the server then honours the source's default/forced flag and picks a track itself. On a source whose default subtitle is image-based (PGS/DVD/DVB) that track cannot go out as a sidecar, so the server falls back to `SubtitleMethod=Encode` and composites it into the video. The cost lands on the *video*, not the subtitle: burn-in rules out remuxing, so an HEVC stream the device could have taken untouched is re-encoded frame by frame. Observed on an HEVC + E-AC-3 + PGSSUB episode, where only the audio actually needed transcoding: the server could not sustain the re-encode in real time, the buffer never grew past a single segment, and playback stalled every few seconds — taking seeking with it, since each seek restarted the encoder and cost seconds before the first frame. The fix is to request `SubtitleStreamIndex=-1` explicitly and to advertise every *text* format we can render (`srt`/`subrip`/`ass`/`ssa`/`vtt`) as `External`, so a subtitle can only ever arrive as a sidecar. Nothing is lost, because the app already fetches subtitle tracks itself and draws them over the video (UR-020) — the server's composited copy was always redundant. Image-based tracks are consequently not offered, which is honest rather than a regression: the renderer cannot composite a bitmap, and the previous behaviour paid for them by making the whole stream unwatchable. Both halves of that hold at the layer that can enforce them. The sentinel travels on the stream URL as well as in the negotiation, because the negotiation is not what opens most streams — a quality switch, a transcoded seek and an audio-track switch each rebuild the URL on their own, and an omitted index there lets the server pick the default track back up out of whatever session state it still holds. And "not offered" is enforced where the offer is made: each subtitle stream crosses the boundary carrying the backend's verdict on whether it can arrive as a sidecar, so the picker lists only tracks the app can draw instead of showing an entry that ticks and displays nothing. Only an explicit "no" hides a track, so a stream carrying no verdict behaves as before | Playback | UR-020, UR-004 | Done |
+| DR-176 | The server is never asked to burn a subtitle into the picture. `PlaybackInfo` omitted `SubtitleStreamIndex`, which does not mean "none" — the server then honours the source's default/forced flag and picks a track itself. On a source whose default subtitle is image-based (PGS/DVD/DVB) that track cannot go out as a sidecar, so the server falls back to `SubtitleMethod=Encode` and composites it into the video. The cost lands on the *video*, not the subtitle: burn-in rules out remuxing, so an HEVC stream the device could have taken untouched is re-encoded frame by frame. Observed on an HEVC + E-AC-3 + PGSSUB episode, where only the audio actually needed transcoding: the server could not sustain the re-encode in real time, the buffer never grew past a single segment, and playback stalled every few seconds — taking seeking with it, since each seek restarted the encoder and cost seconds before the first frame. The fix is to request `SubtitleStreamIndex=-1` explicitly and to advertise every *text* format we can render (`srt`/`subrip`/`ass`/`ssa`/`vtt`) as `External`, so a subtitle can only ever arrive as a sidecar. Nothing is lost, because the app already fetches subtitle tracks itself and draws them over the video (UR-020) — the server's composited copy was always redundant. Image-based tracks are consequently not offered, which is honest rather than a regression: the renderer cannot composite a bitmap, and the previous behaviour paid for them by making the whole stream unwatchable | Playback | UR-020, UR-004 | Done |
 | DR-177 | Each video transcode this device opens is its own server-side job, and the one it replaces is stopped. Jellyfin keys a transcode job by device **and** play session, and every stream URL the app built carried the same hardcoded `DeviceId` with no `PlaySessionId` at all — so the second stream for an item was indistinguishable from the first. Re-opening a stream is not rare: a mid-playback quality switch (UR-074), a transcoded seek and an audio-track switch all do it, each leaving the previous ffmpeg running. Observed on-device when switching bitrate mid-film: the server served the new playlist, then rejected the new job's segments with `400 hls1/main/0.ts` while the two jobs contended for one transcode path, and playback stalled — reproducible against the server, where a second stream for a live job's item alternates between serving bytes and 400ing per attempt, which is what made it read as flaky rather than broken. `begin_video_play_session` mints a session id per open and reports the one it supersedes; the URL builder stops that job (`DELETE /Videos/ActiveEncodings`, un-retried and best-effort — a slow stop must not delay playback, and the new stream no longer collides either way) before returning. Placing it in the URL builder rather than in each caller means every re-open path is covered by construction. Two client faults made the same incident worse and are fixed with it: the fatal-HLS-error handler added the transcode seek offset to a position that already included it, so past roughly the halfway mark of a film any transient network error cleared the "near end" threshold and was reported as end-of-stream — turning a recoverable stall into a skip to the next item, exactly when a quality switch had just made the offset large; and the HTML5 reload primitive resolved on its own `canplay` timeout, so a reload the server never served reported success, leaving the picker showing a quality that was not playing and the caller with nothing to revert | Playback | UR-074, UR-004 | Done |
-| DR-178 | Every position that leaves the app is read from the controller, not from a backend that may not be playing anything. `PlayerController::position()` forwards to the native backend, which is authoritative for exactly one of the three ways this app renders media. On the **webview** path — the shipping default for video on both platforms — nothing is loaded into that backend at all: the `<video>` element is the player, its ticks were re-emitted to the frontend and then dropped, and the backend answered 0 forever. During a **background-audio handoff** the base that converts the stream's relative timeline to the episode's is applied once at the native tick boundary (DR-159), so before ExoPlayer's first tick nothing has applied it and the reading is 0 there too. Both holes surfaced as the same user-visible bug through different doors: returning to the foreground while the audio-only transcode was still opening handed the frontend `0.0`, and the video reloaded at `StartTimeTicks=0` — the episode restarting from the beginning — while the `Stopped` report that followed wrote that zero to Jellyfin as the resume point. `absolute_position()` answers for all three paths: the maximum of the backend's reading, the last position webview-rendered media reported, and the handoff base. The maximum is exact rather than a heuristic, because at most one term is ever meaningful at a time and the base is a floor the stream cannot physically be behind. `duration()` gains the same fallback for the same reason. The element's reading is cleared wherever it stops being the player — teardown, a handoff taking over, a different item loading — so it can never be attributed to what plays next | Player | UR-005, UR-025, UR-040 | Done (pending device verification) |
-| DR-179 | Jellyfin is told what was played: progress while it plays, and a stop when it ends. A device trace of 35 minutes' playback requested `/Sessions/Playing/Progress` **zero** times and sent 14 `Stopped` reports, every one of them at position 0. Three faults, one subject. *Progress never left the device*: the frontend service writes it to the local DB by design, and nothing on the Rust side reported it for webview-rendered media — so the server learned a position only when the player was closed, and a crash or a swipe-away cost the session. It is now reported from the controller's own position ticks, through the 30s throttler it already owned and shares with the native audio path, which covers all three rendering paths in one place instead of adding a second frequent IPC caller. *Zero-position stops were sent*: Jellyfin stores the reported position as the resume point, so a zero does not merely fail to inform, it instructs the server to forget — and no zero was ever real, each one coming from asking a player that was not rendering the media (see DR-178). They are withheld; one landed 40s after the frontend had correctly reported 15:22 for the same episode, overwriting it. *A finished episode reported nothing at all*: Jellyfin decides "watched" from the stop report and its percentage, and in background audio-only mode nobody sends one — the webview is suspended and its element was torn down at the handoff, while the backend advances to the next episode without a word about the one that ended, so an episode listened to end-to-end on the lockscreen never counted as watched. `on_playback_ended` now reports it stopped at its **runtime** (not the last tick, which can be seconds short or, on a handoff whose ticks stopped early, nowhere near the end) before any advance, since after one the queue's current item is the next episode. Scoped to the audio-only handoff, the case the frontend provably cannot cover, so foreground playback keeps its single existing report; music ending natively remains unreported and wants its own change. The reporting seam is a `PlaybackReportSink` the controller sends to, which also collapses three copies of the spawn-a-task-and-hope block into one and is what let all of this be written as failing tests rather than found on a device a second time | Player | UR-025, UR-005, UR-040 | Done (pending device verification) |
-| DR-180 | A background-audio handoff of a **downloaded** episode starts where the video left off. The handoff prefers a local file over the audio-only stream (DR-128), but the two begin in different places and were treated alike: a stream is built with `StartTimeTicks`, so the server makes the handoff point that stream's zero and the base is the handoff position with no seek — while a file has no such parameter and begins at the episode's own zero, so basing it at the handoff position claimed minutes of audio that were about to play from the beginning. Backgrounding a downloaded episode therefore restarted it while the lockscreen scrubber, dutifully adding the base, showed the position it should have been at. `background_audio_plan` splits the two: a file gets no base and a real seek, a stream keeps the base and no seek (seeking one would skip *past* the content by the handoff position again). The same distinction settles an inbound seek — `seek_absolute` re-opens a *streamed* handoff at the requested position because a chunked length-less transcode cannot honour a seek, which is not true of local media, and `resume_stream_at` refuses a non-remote source outright, so routing a lockscreen scrub of a downloaded episode through it failed the seek rather than performing it | Player | UR-040, UR-071 | Done (pending device verification) |
 | DR-161 | Native video is the default, so picture-in-picture has a real surface. DR-160 makes PiP work on the HTML5 path, but that path can only ever shrink the *UI* into the PiP window; showing the video itself needs the SurfaceView behind the WebView, which is what `experimentalNativeVideo` gates. The flag now defaults to on when the user has never chosen, with an explicit stored choice still winning in both directions so anyone who turned it off keeps it off. This is a deliberate acceptance of risk: the flag existed because the native path was an unfinished spike, and `VideoPlayer.scrubRegression.test.ts` documents its history — a native init that flipped to HTML5 mid-lifecycle and left seeks going down one path while ExoPlayer played on another. Those tests pin the **flag-off** interim override (native response overridden to HTML5, backend stopped once), which the default no longer selects, so they now mock the flag off rather than inherit it: they still guard that path, but they no longer describe what ships. The native scrub/seek path is consequently not covered by the suite and needs device verification | UI | UR-041, UR-003 | Needs device verification |
 | DR-159 | The background-audio handoff stops leaking its relative timeline. The handoff plays the episode as a *relative* stream — the audio-only URL is built with `StartTimeTicks` = the position the screen was locked at, so ExoPlayer's zero is the handoff point — and `background_audio_base` holds the offset that turns one back into a real position. The base was a **display-only** correction, applied in exactly two places (the lockscreen scrubber and the internal truncation maths) while every other consumer worked in the relative timeline treating the number as absolute. Each crossing threw away exactly `base` seconds, which is why the jump-back distance varied with where the screen was locked and read as random. Three crossings were live: progress reporting to Jellyfin sent the relative position every 30s, so the server was told `real − base` — and since DR-155 now mirrors the server's position back and refreshes on a cache hit, that regressed value returned as the resume point (lock at 40 min, listen to 90, reopen at 50); lockscreen seeks went out absolute and came back relative, against a chunked length-less transcode that cannot honour a seek at all, so a clamped seek landed at stream zero; and media3's own `seekToDefaultPosition`/`seekBack`/`seekForward` bypassed the `ForwardingPlayer` wrapper entirely, reaching the real ExoPlayer — `Util.handlePlayButtonAction` seeking an ended player to the relative zero being the same mechanism as DR-129's truncation bug through a different door. The fix converts **once, at the boundary**: `JellyTauPlayer`'s position tick adds the base (and shifts the duration with it, since the stream's own length is only what remains) before either `nativeOnPositionUpdate` or the lockscreen sees it, so position updates, progress reports, the frontend and the truncation check all speak the episode's timeline and none needs to know a handoff happened. The base is consequently *removed* from `claim_stream_resume`, `truncated_stream_resume_position` and `player_exit_background_audio`, where adding it now double-counts, and the lockscreen's `positionOffsetMs` addition goes with it (the field remains, read-only, as the tick's input). Inbound seeks go the other way: `seek_absolute` is the new boundary for every outside seek, re-opening the stream at the requested position via `resume_stream_at` when a handoff is active — which is what `onSeekTo` had claimed for months in a comment describing code that did not exist — and an ordinary seek otherwise. `seekToDefaultPosition` is swallowed rather than forwarded, since Rust already owns what "play after the stream ended" means and the `play()` that follows reaches it. Exit reads the position *before* clearing either base, or a tick landing in between hands back a relative one | Player | UR-040, UR-005, UR-025 | Done (pending device verification) |
 | DR-158 | A watched toggle, on the episode row, the season header, the series and movie hero, and the Episode Focus View. Both halves of the backend already existed and neither had a caller: `mark_played` (`POST /PlayedItems`) was reachable only from the sync drain replaying rows the *reporter* had queued, and `clear_watch_history` (`DELETE /PlayedItems`) only from the destructive "erase this series' history" button — so the sole way to mark something watched was to play it. Jellyfin applies both recursively over a season or series, so the container case needs no client-side fan-out *online*. Offline it does: `storage_set_watched` writes the item **and its descendants** (drawn from `items` by `parent_id`/`album_id`/`season_id`/`series_id`, so an uncached id selects nothing and the statement no-ops instead of raising a foreign-key error), because otherwise marking a season watched with no server would tick the season and leave every episode inside it unwatched. It is deliberately separate from `storage_mark_played`, which stays the single-item "this finished playing" path that increments `play_count`. Un-marking clears the resume position as well as the flag, matching the server. `QueuedOp::MarkUnplayed` gives the queue the missing direction — pushing as `clear_watch_history` — so the toggle works offline both ways rather than only one; without it un-marking would have been the half that needed a connection. The button is an everyday toggle, so unlike `ClearHistoryButton` it does not confirm, and it holds an optimistic state because the caller's `watched` prop only catches up after a reload (a season means a round trip, during which the button would otherwise appear to ignore the tap) | UI | UR-073 | Done |
@@ -362,7 +359,7 @@ Internal architecture, components, and application logic.
 | UR-002 | IR-013 | DR-003, DR-012, DR-013, DR-014 |
 | UR-003 | IR-003, IR-004, IR-011 | DR-002, DR-004, DR-010 |
 | UR-004 | IR-003, IR-004, IR-008, IR-011 | DR-002, DR-004, DR-006, DR-129, DR-171, DR-176, DR-177 |
-| UR-005 | - | DR-001, DR-005, DR-009, DR-178, DR-179 |
+| UR-005 | - | DR-001, DR-005, DR-009 |
 | UR-006 | IR-005, IR-006, IR-007, IR-008 | - |
 | UR-007 | IR-010 | DR-007, DR-008, DR-016 |
 | UR-008 | IR-010 | DR-007, DR-011 |
@@ -382,7 +379,7 @@ Internal architecture, components, and application logic.
 | UR-022 | IR-017 | DR-025 |
 | UR-023 | IR-010 | DR-026, DR-047, DR-048, DR-049 |
 | UR-024 | IR-010 | DR-027 |
-| UR-025 | IR-015 | DR-028, DR-131, DR-132, DR-178, DR-179 |
+| UR-025 | IR-015 | DR-028, DR-131, DR-132 |
 | UR-026 | - | DR-029, DR-048, DR-050 |
 | UR-027 | IR-020 | DR-030 |
 | UR-028 | - | DR-031 |
@@ -397,7 +394,7 @@ Internal architecture, components, and application logic.
 | UR-037 | IR-010 | DR-042 |
 | UR-038 | IR-010 | DR-043 |
 | UR-039 | - | DR-045, DR-046 |
-| UR-040 | IR-025 | DR-051, DR-052, DR-129, DR-130, DR-159, DR-178, DR-179, DR-180 |
+| UR-040 | IR-025 | DR-051, DR-052, DR-129, DR-130, DR-159 |
 | UR-041 | IR-026 | DR-053, DR-160, DR-161, DR-172 |
 | UR-042 | IR-009, IR-014 | DR-054 |
 | UR-043 | IR-027 | DR-055 |
@@ -427,7 +424,7 @@ Internal architecture, components, and application logic.
 | UR-068 | - | DR-119 |
 | UR-069 | - | DR-113, DR-114, DR-120 |
 | UR-070 | - | DR-121, DR-122 |
-| UR-071 | IR-032 | DR-123, DR-124, DR-125, DR-126, DR-127, DR-128, DR-133, DR-134, DR-135, DR-136, DR-137, DR-138, DR-170, DR-171, DR-180 |
+| UR-071 | IR-032 | DR-123, DR-124, DR-125, DR-126, DR-127, DR-128, DR-133, DR-134, DR-135, DR-136, DR-137, DR-138, DR-170, DR-171 |
 | UR-072 | - | DR-156 |
 | UR-073 | - | DR-158 |
 | UR-074 | - | DR-162, DR-177 |
@@ -599,16 +596,10 @@ Internal architecture, components, and application logic.
 | UT-160 | The default row height suits its container: it grows with the width, stays inside its bounds, and at phone width still fits two 16:9 tiles side by side | DR-174 | Done |
 | UT-161 | A collection type maps to its favourites scope (`movies`/`tvshows`/`music`), every other kind — Live TV, channels, box sets, books, unknown — maps to none rather than to `All`, and a constructed library carries the scope across the wire as `favoritesScope`, omitted entirely when it has none | DR-175 | Done |
 | UT-167 | The mosaic's composition: the cross-library favourites entry leads, each library is followed by its own category tile pointing at that category's tab, a category shared by two libraries still yields one tile, a library kind favourites do not carve up yields none, a scope the page offers no tab for is ignored, and every tile is uniquely keyed | DR-174, DR-175 | Done |
-| UT-168 | Subtitles are negotiated as sidecars, never burned in: the requested `SubtitleStreamIndex` is the explicit "none" sentinel (`-1`) rather than omitted, every text format we can render (`srt`/`subrip`/`ass`/`ssa`/`vtt`) is advertised as `External`, and the burn-in verdict is by format — text never forces it, image formats (PGSSUB, dvdsub) always do, case-insensitively. The same sentinel rides the stream URL itself, so a stream re-opened without a fresh negotiation cannot inherit a subtitle. And the verdict reaches the picker: a subtitle stream carries `supportsExternalDelivery` — set only for subtitles, `false` for a bitmap format and for one the server left unnamed — which drops the tracks the app could never draw from the menu, the `<track>` children and the native play request alike, without even fetching their URLs, while a stream carrying no verdict at all is still offered | DR-176 | Done |
+| UT-168 | Subtitles are negotiated as sidecars, never burned in: the requested `SubtitleStreamIndex` is the explicit "none" sentinel (`-1`) rather than omitted, every text format we can render (`srt`/`subrip`/`ass`/`ssa`/`vtt`) is advertised as `External`, and the burn-in verdict is by format — text never forces it, image formats (PGSSUB, dvdsub) always do, case-insensitively | DR-176 | Done |
 | UT-173 | Every video stream URL carries a `PlaySessionId`, each open mints a fresh one, and the open reports the session it superseded so that job can be stopped | DR-177 | Done |
 | UT-174 | A fatal HLS network error is read against the *absolute* position: mid-film — including after a quality switch, where the seek offset carries the whole resume position — it is retried rather than reported as the end of the stream, the last tenth of a known runtime is treated as the end, an unknown runtime retries, and retries stop once the budget is spent | DR-177 | Done |
 | UT-175 | A stream reload that never becomes playable is reported as a failure instead of resolving as success, so the caller can revert its selection rather than leave the UI claiming a stream that is not playing | DR-177 | Done |
-| UT-176 | A handoff's position is floored at its base: with no tick yet landed the exit position is the point the screen was locked at rather than 0, and once ticks are flowing (the base already applied natively) it is not added twice | DR-178 | Done |
-| UT-177 | Webview-rendered media's reported position and duration are the controller's, and are dropped the moment that element stops being the player — on teardown, and when a handoff takes over | DR-178 | Done |
-| UT-178 | A stop report at position 0 is withheld rather than sent (it would clear the resume point), while a real position is still reported from either rendering path — the element's on the webview path, the backend's on the native one | DR-179 | Done |
-| UT-179 | An audio-only episode that ends naturally is reported stopped at its runtime, so Jellyfin marks it played; a truncated stream, which is about to be re-opened, reports nothing | DR-179 | Done |
-| UT-180 | Position ticks report progress to the server, throttled to one report per item per window rather than one per tick | DR-179 | Done |
-| UT-181 | The handoff plan matches its source: a downloaded file takes no base and a seek, a stream takes the base and no seek, and a handoff at 0:00 takes neither; a downloaded handoff's absolute seek stays an ordinary seek instead of a stream rebuild | DR-180 | Done |
 | UT-153 | Scroll handling per navigation kind: a forward move always lands at the top even when the previous page was scrolled and even when the target was visited before, Back restores that route's own saved offset (and the top when it has none), offsets are kept per route rather than shared, a repeated Back still restores, and the initial load leaves the container alone | DR-156 | Done |
 | UT-142 | The audio codecs offered for video direct play: a Dolby device's real `MediaCodecList` output drops `ac3`/`eac3`, AMR and raw PCM are dropped too, a fully-supported list is passed through untouched, a list with nothing decodable still claims `aac`, and stray spacing or casing does not decide whether the user gets sound | DR-148 | Done |
 | UT-143 | Subtitle URLs resolve to plain strings before they reach the markup (never a Promise), unresolvable tracks are dropped, a stale selection collapses to "Off", and a server-default track is never auto-selected | UR-020, DR-023 | Done |