iptvnator/docs/architecture/vod-multi-source.md

# VOD Multi-Source

Finds the same movie in the user's other imported playlists, lets them switch
which one it streams from without losing the timecode, and turns the
playback-error screen into a recovery point.

The point is not choice for its own sake — it is rescuing a viewing when the
current source is dead, serves an unsupported codec, or buffers badly.

## Scope (v1)

| | |
|---|---|
| Source types | **Xtream ↔ Xtream only** |
| Content | Movies only — series are not offered a source chip |
| Environment | **Electron only** — the chip renders nothing in the PWA |
| Auto-failover | Opt-in, **off by default** (`Settings.vodAutoFailover`); offered only on the built-in web players |
| Pin scope | Per movie (a global portal priority is out of scope) |
| Stream probe | HEAD → reachable + latency, sent with the playlist's own playback headers. **No codec probing** |

Stalker never reaches the `content` table (it would need a live authenticated
`get_ordered_list&search=` per portal), and M3U playlists are stored as a JSON
blob whose search path forces `content_type: 'live'`. Both are additive later
without changing the contracts — `VodSourceCandidate.portalType` already carries
`'xtream' | 'stalker' | 'm3u'` and discovery sits behind a service interface.

A probe answer is cached per *request*, not per URL: two playlists can share a
stream URL and require different headers, and one of them answering 403 says
nothing about the other.

`ffprobe`/`ffmpeg` are not dependencies of this app and are not bundled, so
`provenance: 'probe'` means reachability and latency only. There is deliberately
no feature flag for codec probing: it would gate a code path with no binary
behind it.

## The honesty rule

This is the part to preserve if anything here is refactored.

Every metadata value carries **where it came from**:

| provenance | produced by | rendered as |
|---|---|---|
| `api` | `get_vod_info` — container, codec, audio, dimensions | plain tag |
| `parsed` | regex over the title/filename | tag prefixed `~`, warn colour |
| `probe` | HEAD → reachable + latency (retried as a ranged GET when the server answers 405/501, since plenty serve media over GET while refusing HEAD) | `ok` / `fail` status tag |
| *absent* | — | **no tag at all** + a `check` chip |

Three rules follow, and each is enforced in code rather than by convention:

1. **A guess never ranks.** `factualOnly()`
   (`libs/portal/shared/data-access/.../vod-source-metadata.util.ts`) is the only
   sanctioned accessor for ranking and failover decisions, and `parsed` values
   are structurally unreachable through it. A filename claiming 4K cannot
   outrank a source that was actually reached.
2. **Unknown is not "unavailable".** `VodSourceProbeStatus` separates `fail`
   (contacted and refused) from `unknown` (timed out, blocked by the redirect
   policy, or no probe capability). A probe returning HTTP status `0` maps to
   `unknown`; the UI keeps offering a check and never shows the source as dead.
3. **Empty beats wrong.** Quality is derived from pixel *width*, because
   letterboxed masters are cropped vertically — a 2.39:1 1080p film is 1920×800,
   and 800 alone is indistinguishable from a 1280×800 encode. With no width, a
   height is trusted only within 5% of a standard frame height; otherwise no tag
   is emitted. Below the HD widths the ranges stop working: 800×600
   and 800×450 are neither 480p nor each other, and 720 wide is NTSC 480p or
   PAL 576p depending only on the height. Those formats are therefore matched
   rather than bucketed, and an unrecognised shape returns nothing rather than
   a label that would be published as an `api` fact. A known height still has
   to be consistent with the match: cropping only ever *removes* lines, so a
   shorter frame is a letterboxed master of that format, while a taller one
   (640×480 against 640×360) is a different shape and gets no tag.

Provenance is per-field and changes over time: at discovery a row has only
`parsed` tags, because the `content` table stores no container, codec or audio.
Facts arrive when the source is resolved.

## Architecture

```
VOD details page (Xtream)
  └── VodMultiSourceHostService          component-provided, one per open movie
        ├── VodMultiSourceController     session state + failover ranking
        ├── VodSourceDiscoveryService ──► DB_FIND_TITLE_SOURCES (trigram FTS)
        ├── VodSourceResolverService  ──► foreign playlist creds → get_vod_info
        │                                  → constructVodUrl
        ├── VodSourcePinService       ──► DB_GET/SET/CLEAR_VOD_SOURCE_PIN
        └── StreamProbeService        ──► STREAM_PROBE_URL (main process)
```

`VodMultiSourceHostService` is **component-provided, never root-provided**: the
controller's "each source is tried at most once" set must die with the movie, or
a later film inherits a poisoned failover history.

`VodMultiSourceController` is a plain class, not a service, for the same reason —
and so its ranking logic is testable without TestBed.

### Ownership

| Concern | Location |
|---|---|
| DTOs, match key | `libs/shared/interfaces/src/lib/vod-source*.ts` |
| Pin table | `libs/shared/database/src/lib/vod-source-pins.schema.ts` |
| Discovery SQL | `apps/electron-backend/.../operations/title-sources.operations.ts` |
| Pin CRUD | `apps/electron-backend/.../operations/vod-source-pin.operations.ts` |
| Probe handler | `apps/electron-backend/src/app/events/stream-probe.ts` |
| Discovery / resolve / rank | `libs/portal/shared/data-access/src/lib/multi-source/` |
| Probe + pin clients | `libs/services/src/lib/{stream-probe,vod-source-pin}.service.ts` |
| Row / popover / chip | `libs/ui/components/src/lib/vod-sources/` |
| Page wiring | `libs/portal/xtream/feature/src/lib/vod-details/vod-multi-source-*.ts` |

### One picker, two places, two counts

The chip on the action row and the chip in the inline player's now-playing bar
are the same component, so both are handed the same `matchKind` and the same
`vodAutoFailover` value and both write the setting back. A copy that rendered
the toggle off while it was on — and did nothing when flipped — would be worse
than not offering it.

The two numbers around it are deliberately different, because their sentences
are: the chip says "Sources N" and counts alternative **streams**, while the
caption says "also found in N other playlists" and counts distinct
**playlists** (`alternativePlaylistCount`). The popover groups a portal's three
copies of a film under that one portal, so counting rows there would contradict
the list the caption invites the user to open.

## Identity

Provider ids cannot key a pin — the same film has a different `stream_id` in
every portal, which is the problem being solved.
`buildVodSourceMatchKey()` produces `tmdb:{id}` when a usable TMDB id exists,
otherwise `title:{normalizedBase}:{year}` via the shared `normalizeTitleKeys`.

Enrichment adds BOTH identifying fields late, so the same movie can already be
pinned under any poorer form of itself:

| pinned when | stored under |
|---|---|
| after enrichment | `tmdb:{id}` |
| before the TMDB id | `title:{base}:{year}` |
| before the year too | `title:{base}:` |

`buildVodSourceMatchKeyCandidates` returns all three, most-trusted first.
Reading every alias is what keeps a late TMDB id from orphaning an earlier pin.

Three key sets, because reading, writing and deleting are different questions
(`pinKeysFor` builds all three so they cannot disagree):

| set | contents | why |
|---|---|---|
| `lookup` | every alias above | a pin may sit under any poorer form of the movie |
| `write` | `tmdb:` + `title:{base}:{year}` | keys that name exactly ONE film |
| `loaded` | the key the pin on screen came from | the only ambiguous row this session may retire |

A write stores the canonical key and clears the stale ones — both halves
matter, and each rules out the other's shortcut:

- Writing only the top key would leave the lower-trust aliases pointing at
  whatever was pinned before, and a reopen that reads one of those (enrichment
  has not landed, or its request failed) starts the source the user replaced.
- Writing the decision *into* every alias is not the fix either: the yearless
  form is shared by every remake, so a known-year pin stored there would answer
  for a different film — pin Dune (2021), open Dune (1984) before its year
  arrives, and it starts the 2021 source.

A write stores the new key **before** retiring the old rows. The other order
destroys the stored preference and can then fail to replace it, leaving nothing
persisted while the row still shows the old pin; lookups are most-trusted-first,
so a leftover alias never outranks the key just written.

The pin a rediscovery reads is applied **immediately**, not after its source
lookup returns: holding that snapshot across the await lets it overwrite a pin
the user makes in the meantime, leaving the row and the primary Play naming a
source the database no longer holds. Applying it first makes the later write
simply win.

For the same reason a write or an unpin never *deletes* the yearless alias on
spec: that row may hold another remake's preference. The single exception is
the row this session actually read, because the user is acting on the pin they
can see — and leaving that one would make an unpin come back.

The row only changes once the write lands. A pin the database refused is worse
than no pin at all — the icon promises the preference will be there next time,
and it will not be — so `togglePinnedSource` reports "nothing happened" and the
controller is left exactly as it was.

### Rediscovery vs. a new session

Two keys, deliberately, because the host has two different questions to answer
when enrichment lands:

- `vodMultiSourceMovieKey` covers title, year and TMDB id. Enrichment changing
  any of them **re-runs discovery** — that is how a yearless search gets its
  year and a `tmdb:`-keyed pin becomes findable.
- `vodMultiSourceSessionKey` is `playlistId:contentId` — the film itself. It is
  what decides whether that rerun is a *refresh* or a *new session*.

A refresh keeps the controller: the source the user switched to stays active
(with the facts its resolve produced, rather than the catalog's guesses), the
tried set stays burned, the live position stays, and a switch already in flight
still commits. Rebuilding there would take the film off the source it is
actually streaming, and hand failover a clean slate for sources it has already
spent. Only a different film resets — including the tried set, which is what
makes failover terminate.

A rerun can also legitimately *drop* the playing row: the year the enrichment
supplies makes the year gate reject a copy the yearless search had admitted
("Dune" 1984 while watching the 2021 film). Off the list is right — it is not
the same film. Off the screen is not, so `applyDiscoveredSources` keeps it as a
row and leaves it active; a caption naming a playlist that is not streaming
anything would be a lie about the one thing this feature exists to state.

## What the queries are allowed to miss

A source that exists but is never read is indistinguishable, to the user, from
one that does not exist — the chip simply does not appear. So:

- **The current playlist is excluded in SQL**, not afterwards. It routinely
  lists a film in several categories, and those rows would otherwise spend the
  FTS window before a single other playlist was read.
- **Duplicates collapse in SQL too**, for the same reason. One playlist can
  list a film in dozens of categories, and those rows rank identically, so
  `GROUP BY cat.playlist_id, c.xtream_id` runs before the limit. Collapsing
  them only in TypeScript afterwards cannot recover the playlists the window
  never reached.
- **Short titles scan on a word boundary, and take no window at all.** The
  trigram tokenizer cannot index tokens under three characters, so "Up", "It"
  or "Us" produce an empty `MATCH` and fall back to a scan. A substring scan
  matches "Titanic" and "The Italian Job" for "It", so the scan asks for the
  token as a word
  (`' ' || LOWER(title) || ' ' GLOB '*[^a-z0-9]it[^a-z0-9]*'`) and orders by
  title length (a match is the title plus decoration: "IT (2017) 1080p").

  The FTS path keeps its 60-row window because it ranks by relevance — the best
  rows are the ones it keeps. A scan cannot rank, so a window there would
  silently decide which valid sources the user may see, and it would not even
  buy anything: the GLOB cannot use an index, so SQLite reads every row either
  way and a `LIMIT` saves transfer, not work. What bounds the scan instead is
  its predicate: reaching it means NO token cleared the trigram minimum — a
  one-or-two-character title like "It", but also an all-short multiword one
  like "I Am" — and EVERY token must then appear as a word. Matching on the
  first token alone would return most of a large catalog for the confirmation
  pass to discard, which on the single database worker is real blocking.

  Like the `LIKE` it replaces it compares ASCII-lowercased text, so a non-ASCII
  short title is no better and no worse served than before.

Both remain necessary-not-sufficient filters: the two-tier normalized
confirmation still runs afterwards, so the looser query never admits "Upgrade"
for "Up".

One row inside the excluded playlist is kept when the caller names it
(`keepContentId`): a pin can point at another copy of the film in the playlist
being viewed, and dropping that row would leave the preference pointing at
nothing. The host therefore reads the pin BEFORE discovery. When that pin is
the route's *own* row, the kept copy and `currentSourceRow()` are the same
stream, so `applyDiscoveredSources` drops the duplicate rather than listing it
twice.

### Same title, different film

The year gate applies to **both** match tiers, not just the year-stripped one.
`normalizeTitleKeys` strips bracketed segments wholesale — they usually hold
quality and language tags — so "Dune (1984)" and "Dune" normalize to the same
string and the exact tier would accept the remake without ever consulting a
year, ranked *above* every fuzzy match. Discovery reads a bracketed year out of
the raw title first, and when both sides state a year and they disagree, it is
not the same movie. An unknown year still never blocks.

## Why resolution is lazy

The `content` table stores no `container_extension`, and
`XtreamUrlService.constructVodUrl` returns `''` without one. A discovered source
is therefore **not playable from the database** — every alternative costs one
live `get_vod_info` against a foreign playlist's credentials, which can fail
offline, on an expired account, or behind Cloudflare.

So: rows render instantly from the FTS match with `parsed` provenance, and a URL
is resolved only when the user clicks play, pins, or checks. Containers are
memoised per `(playlistId, streamId)` for the session, and a container learned
earlier is reused if the portal later goes unreachable. Resolution is never
fanned out on page load.

## Switching without losing the timecode

Every playback host renders `@if (inlinePlayback(); as playback)`, so re-`set()`ing
that signal with a new `{streamUrl, startTime}` swaps the source **in place** —
the player component, `WebPlayerView` and the engine all survive, and
`WebPlayerViewComponent`'s effect rebuilds the source and clears the diagnostic.

Three details make the position survive:

- The carried position is the **live** one. `handleInlineTimeUpdate` reports to
  `VodMultiSourceHostService.reportPosition()` *before* the 15-second
  persistence throttle, so a switch does not rewind by up to 15 seconds.
  External players have no `timeupdate` at all, so for them the polled
  `playback_positions` value IS the live one and is reported directly —
  seeding it would freeze the resume point where playback started.
- It is a single `.set()`, never `null` then set — a null in between would
  destroy the player subtree and lose the engine.
- `playback_positions` is keyed `(playlistId, contentXtreamId, contentType)`, so
  a switch changes the key. The resolved playback carries the **new** source's
  `contentInfo`, and that source's row takes over.

The position also has to exist *before* anything plays. Nothing reports a live
one until the first `timeupdate`, so a pinned source started straight off the
Resume button would resolve at zero and restart the film. The controller is
therefore seeded from the persisted position (`seedResumeSeconds`), one-way:
once a live position exists it wins, because the stored one lags it by up to
the save throttle and applying it would visibly rewind.

A resuming engine can emit a `timeupdate` at ~0 before it finishes seeking.
`VodDetailsPlaybackService` guards this with a one-shot `resumeSettled` latch —
a filter would have broken deliberate seek-backwards. The latch also releases
when the target is out of reach: switching a two-hour position into a
90-minute cut means the engine can never report it, and waiting would suppress
every save for the rest of the session. `handleInlineTimeUpdate`
returns that verdict and the route feeds multi-source the `startTime` it asked
for until the engine gets there, so a switch or a failure during the initial
seek does not resolve the next source at zero and restart the film. One latch
serves both, because two would eventually disagree.

## Failover

Only fires when `Settings.vodAutoFailover` is on, and it first awaits a
discovery still in flight — a stream can fail faster than SQLite answers, and
concluding "nowhere to go" against an empty controller would strand the user on
the error screen with alternatives landing a moment later. `stillOwnsScreen()`
does that wait and then re-checks the session, because the user can navigate
during it and the controller afterwards may belong to a different film; the
pinned-Play path takes the same wait, or a persisted pin would lose to worker
latency.
Ranking (`pickFailoverTarget`):

1. never tried this session — a **hard filter**, not a preference
2. probed reachable; probed failing is penalised
3. not known to have failed recently
4. richer **factual** metadata (via `factualOnly`)
5. exact title match over fuzzy

Termination is structural: `triedSourceIds` only ever grows within a session, so
an N-source movie fails over at most N−1 times and then shows the honest error
screen. Returning to an earlier source by hand does not clear the set.

Selection is not an attempt. `setActiveSource` only selects; `markPlaying` also
spends the source's turn, and only the three places that really start playback
call it — a switch, the route's own Play/Resume, and restoring the playing row
after a rediscovery. Discovery selects the route's row the moment the page
opens, and a pin or the picker can select an alternative before anything plays;
counting those would let a later failure skip a healthy fallback, or call the
options exhausted with one untouched. `runFailover` then retires whatever is on
screen before picking, so the source that just failed is spent however it got
there — one hole per start path would be an infinite ping-pong between two
sources.

A source that cannot even be resolved is marked tried without becoming active,
and failover **continues to the next candidate** rather than giving up —
production calls `failover()` only once, on the original failure, so stopping at
a dead top-ranked source would strand every healthy one below it. `switchTo`
therefore reports which of two things happened: `unresolvable` (marked tried,
keep going) or `superseded` (something newer owns the screen, stop). Without
that distinction the loop would spin on a superseded target forever, because
only the first outcome marks the candidate tried.

**A pin is not decoration.** The primary Play action starts from the pinned
source when one is set, and the pin outranks every other signal in the ranking
above. Loading a pin that only decorated its row would mean "make this the main
source" survived a restart as an icon and nothing else.

The switch is **always announced** — another source can carry a different dub or
cut. The toast offers Undo, and adds a dub warning when
`audioDiffersFactually()` is true, which requires **both** sides to state an
audio track as fact. Two guesses, or a guess against a fact, stay silent.

Web engines only (HTML5/hls.js, Video.js, ArtPlayer). Embedded MPV suppresses
shared diagnostics and owns its own error block; external MPV/VLC are
fire-and-forget with no error channel back.

## External players and an alternative source

A switch goes through the same inline-vs-external fork a normal Play takes, so
with MPV or VLC configured the alternative opens in the external player — and
that session carries the OTHER playlist's ids. `matchedExternalPlayback` would
disown it: the primary button never became Stop, stopping found no session, and
another click opened a second player. The page therefore claims a session that
matches either the route's own stream or the alternative multi-source says is
active (`VodDetailsPlaybackBindings.activeSource`).

`ownsContent()` answers that question once, for both consumers: the session
matcher AND the playback-position bridge. They cannot be allowed to disagree —
a page that shows a Stop button for a session whose progress it discards keeps
the resume point at wherever playback began, so a switch an hour later rewinds
the whole session.

The caption itself appears only while a player is actually running — inline or
a matched external session, and not while a playback diagnostic is up.
Discovery marks a source active as the page opens, so gating on that alone
would have the page claim "Playing from …" before Play was pressed, after the
player was closed, and over the error screen for a stream that would not
play.

Whichever source ends up playing, the "playing" badge follows it: starting the
route's own stream (Play, Resume, Restart, or the fallback after a pin does not
apply) hands the badge back to the route row, or the picker and caption go on
naming an alternative that is no longer running. That hand-back also
invalidates a switch still resolving — the user chose the route stream, and an
older resolution arriving afterwards would replace what they just asked for. And a source started through
the picker or a pin is recorded in Recently Viewed exactly as an ordinary Play
is — it is the same film, watched.

Stop then has to win over the pin. The primary action consults the pin first —
that is what makes "make this the main source" decide where playback starts —
but when a session is already running the same button reads Stop, and doing
anything other than stopping would launch a second player while the first kept
going.

## PWA

Discovery, foreign-playlist reads, the pin table and the probe are all
main-process. A browser HEAD to an arbitrary IPTV host is CORS-blocked, and
`no-cors` yields an opaque response where 200, 403 and 404 are
indistinguishable — so the PWA cannot answer these questions honestly rather
than merely lacking a convenience.

Every entry point is gated on a bridge `typeof` check (`isAvailable`), matching
`CatalogTitleMatchService`. In the PWA the chip renders nothing and the
auto-failover setting is hidden.

## Resuming a pinned copy

Playback positions are keyed by (playlist, stream), so a pinned alternative
carries its own. `playPinned` looks that position up and applies it — and
applies **zero** when the lookup comes back empty, because the controller is
still holding the ROUTE copy's position at that moment. Carrying it across
would drop the user into the middle of a film they never started here, and the
first save would write that timecode under the pinned source's key.

When no lookup function is supplied at all, nothing is applied: "never watched"
was never established, so there is nothing to correct.

## What the primary button describes

Two position signals, not one. `vodPlaybackPosition` is the LAST position
seen — whichever copy produced it — and feeds the progress bar and the switch
handoff. `routePlaybackPosition` is the route copy's own row, and everything
that acts on the route's stream reads that: Resume, its label, its timecode.
Collapsing them lets an alternative's progress resume the route copy at a
timecode nobody reached in it. Route reuse (the Similar rail) clears
both, so the button cannot describe the previous movie while the new lookup is
still in flight, and every route start — including the primary button's
fall-through past an unresolvable pin — goes through the route's own wrappers,
which replace whatever timecode an alternative left in the controller.

While the pinned copy is the one playing, its live position wins over the row
that was stored before this session started.

A pin means the button plays a copy the page did not load a position for. A
watched-through copy resolves to zero rather than its stored seconds, through
the same `isResumablePosition` rule the label uses — otherwise the button reads
Play and then seeks back to where the film ended. Restart follows the pin for
the same reason: with Resume honouring a pinned copy, a Restart that started
the route copy would silently switch the user's playlist.
`createPrimaryActionPosition` therefore looks that copy's row up and lets it
govern the label, the timecode and the Restart affordance — including when the
lookup comes back empty, because "never watched" is an answer: the button must
read Play, not `Resume 42:18` on a stream that starts at zero. A pin on the
route's own row changes nothing; the loaded position already IS that copy's.

## Provider codec metadata

`info.video` / `info.audio` come back in two shapes: the declared string array
(`['H.264']`, which the mock server and many panels send) and the ffprobe
object carrying `codec_name`/`width`/`height`. `readStreamInfo` accepts both —
reading only the object silently lost the codec on every array response, and
with it the "dub may differ" warning, which compares stated audio tracks.

Switching sources through `startResolvedPlayback` closes the external session
it LAUNCHED first — tracked separately from the controller's active source,
which a switch has already moved to the destination by then. It REPLACES what is playing — with MPV or VLC and instance
reuse off, the backend would otherwise spawn a second detached player, leaving
both sources running and Stop owning only the newer one.

## Short titles and Unicode

SQLite's `LOWER()` and GLOB character classes are ASCII-only, so a short
non-ASCII title could not be folded or word-bounded and simply never matched —
the film stayed absent from the chip. The ASCII/Unicode branch is decided from the RAW token, not the normalized
one: normalization folds diacritics, so "Ça" arrives as "ca" and looks like
plain ASCII while the stored title still reads "Ça". ASCII tokens keep the
word-boundary GLOB
(what stops "it" matching "Titanic"); a non-ASCII token falls back to a
substring test against both the folded and the as-typed form. That covers a
title stored in the same case as the request or in lower case, and deliberately
does not claim full Unicode case folding. It is looser, and the normalized
confirmation afterwards is what makes looser safe.

## Claims about the present

`isActive` means "the source a switch or Play would use" — selection, not
playback. `pinnedSourceAwaitingPlay` therefore takes `playbackLive` as well:
a pinned row stays selected after its player is closed, and skipping the pin
on selection alone would send the next Play to the route copy. Discovery sets it the
moment the page opens, and it survives closing the player — so it cannot, on
its own, back a statement in the present tense.

`VodDetailsRouteComponent.playbackLive` is that statement. Inline, it needs a
`timeupdate`: `inlinePlayback()` is only the REQUEST to play, non-null while
the engine is still opening the stream and still non-null after it fails, while
a timeupdate is the engine reporting frames. External, it needs the session
past `launching`. Every path that mounts a stream clears the latch first —
Play, Restart, and a source switch, which puts a DIFFERENT stream into the
same host and so cannot inherit the old one's evidence.

Two things read it, and they must agree: the "Playing from" caption, and the
source row's badge — which reads `Current` when a source is merely selected and
`Playing` once one really is.

## Where the route's code lives

`VodDetailsRouteComponent` is a thin host. The multi-source concerns it grew
live in `VodDetailsMultiSourceUiService` (component-provided): the
`playbackLive` evidence, the caption, the primary button's position, the
source actions, and the failover toast. The "Similar" rail and offline
downloads sit in their own component-provided services beside it.

## Backup

`playPinnedSource` reports `played` / `superseded` / `unavailable`, and only
`unavailable` may fall through to the route source. Collapsing the first two
meant a double-click on Play — where the second attempt supersedes the first —
had the losing attempt conclude "no usable pin" and start the route stream over
the playback the winning one had just begun. Same distinction as `runFailover`'s,
for the same reason.

A pin is written and its old aliases retired in ONE transaction
(`setVodSourcePin(db, pin, retireKeys)`). Split in two there is no honest
outcome for a half-failure: a surviving alias is read before the canonical key
on the next open, so reporting success starts the source the user just
replaced — while reporting failure leaves the canonical row durable and the UI
showing a pin that is no longer the stored one.

Pins ride along with playlist backup, under the playlist they point at, as the
optional `sourcePins` collection. See
`docs/architecture/playlist-backup-restore.md` for the remapping and
sanitizing rules — the short version is that `matchKey` names the film and
survives as-is, while the playlist id becomes the imported copy's.

## Which engines can fail over

Only the built-in web players (HTML5, Video.js, ArtPlayer) raise the playback
diagnostic that reaches `onPlaybackFailed()`. `WebPlayerViewComponent`
suppresses it for Embedded MPV, and external MPV/VLC never mount that component
at all — a stream that dies there is invisible to the app.

So the toggle is hidden, not merely inert, on those engines: in
`Settings > Playback` (`reportsPlaybackFailures()` gating the row) and in the
sources menu (`autoFailoverSupported`). Leaving it visible would let a user
switch on a feature that can never fire. The stored preference is untouched by
the change — switching back to a web player restores whatever was set.