android: the media mirror grows a queue window the card never shows

The Kotlin side of the mirror has always known about exactly one track, and
media3's `SimpleBasePlayer.getState()` — the thing an Android Auto session is
built on — wants a playlist and an index into it. So the data lands a round
before the migration that needs it, where it cannot break anything:
`NowPlaying` and `NowPlayingArgs` carry a bounded `queue` of at most
twenty-one entries, the current item and ten either side, each with its id,
title, artist, album, duration and art key, plus `queueIndex`, where the
current one sits within that window rather than within the whole queue.
`src/mobile/media.svelte.js` fills them from `player.queue` and `player.qi`;
`MediaService` ignores every bit of it, so the card is byte for byte the card
it was. Ten either side because one covers the card's own prev and next and
nothing else while a queue list — which is what Auto asks for — wants a
screenful plus a scroll both ways, and it is a cap rather than a length: a
two-thousand-track queue crosses the bridge as twenty-one entries exactly
like a twenty-one-track one, measured at two kilobytes of JSON for twenty-one
short titles and six with long ones and real cover paths, against the thirty
to eighty of base64 cover that already ride the same call once per record.

Nothing renders it, which is the whole difficulty in checking it — and both
hops of this bridge fail silently, because serde drops an unknown field and
tauri's Jackson mapper has `FAIL_ON_UNKNOWN_PROPERTIES` off, so a key spelled
snake_case where camelCase was wanted arrives as nothing at all with no error
anywhere. `MediaSessionPlugin.update` logs one line per update, and the phone
walk holds that line against `__ss.card` — the mirror media.svelte.js now
keeps of what it last sent, the shape xfernote has kept of the shade since it
was written — field for field, through a next and a previous. The art-key
count is compared as well as the size and the index, since that is the only
camelCase field an entry has. The check arms at queue index one rather than
at wherever the walk left off, which buys a row on either side — `prev()`
seeks to zero at the top of a queue and `next()` stops at the end — a track
that has only just started, so `prev()` is still a step rather than the seek
it becomes past five seconds, and a window whose own index is the queue
index, because nothing is clamped off the front while the index is under ten.
Each of the three readings has to be a fresh one at both ends, the push
counter up and a new line in the log, since a `prev()` that lands back where
it started reads exactly like a stale line otherwise; and a queue too short
to arm, or repeat-one, under which `next()` seeks instead of stepping, fails
the check rather than skipping it.

The plugin's `consumer-rules.pro` keeps the new `@InvokeArg` class by name
beside the one it already keeps; without that line a release build would fill
`NowPlayingArgs` and leave every queue entry null, quietly. Rust and Kotlin
both changed, so this one cannot go down `dev.sh` — it needs the full
`deploy.sh` detour. And everything the walk already asserts about the card is
untouched, which is the real check on this round.

ANDROID.md

@@ -857,6 +857,50 @@ with a `ClassNotFoundException`. `src-tauri/android/build.sh` exports it;
 after adding a plugin, touch `src-tauri/build.rs` too, so the app's build
 script re-runs and rewrites the wiring.
 
+Every update also carries a **queue window** that nothing reads. `NowPlaying`
+(Rust) and `NowPlayingArgs` (Kotlin) hold a `queue` of at most twenty-one
+entries — the current item and ten either side, each with its id, title,
+artist, album, duration and art key — plus `queueIndex`, where the current one
+sits *within that window* rather than within the whole queue.
+`src/mobile/media.svelte.js` fills both from `player.queue` and `player.qi`;
+`MediaService` ignores them completely, so the card is byte for byte the card
+it was. The reason is media3: `SimpleBasePlayer.getState()` wants a playlist
+and an index into it, and the data that migration needs should have been
+running on the phone for a while before anything depends on it. Ten either
+side because one covers the card's own prev and next and nothing else, while a
+queue *list* — which is what Auto asks for — wants a screenful plus a scroll
+in both directions; and it is a cap, not a length, so a two-thousand-track
+queue crosses the bridge as twenty-one entries exactly like a twenty-one-track
+one does. Measured at two kilobytes of JSON for twenty-one short titles and
+six with long ones and real Android cover paths, against the thirty to eighty
+kilobytes of base64 cover that already ride the same call once per record —
+and an update is a track change, a transport change or the thirty-second
+top-up, never a position tick.
+
+Because it is on no screen, the walk reads it out of `logcat`:
+`MediaSessionPlugin.update` logs one `media window n=… i=… art=… at=…` line
+per update under the tag `SoulStream`, and the phone walk's `queue-window`
+check holds that against `__ss.card` — the mirror `media.svelte.js` keeps of
+what it last sent, beside xfernote's — field for field, through a next and a
+previous. Field for field is deliberate: a key spelled snake_case where the
+bridge wants camelCase arrives as nothing at all on both hops, with no error
+anywhere, which is why the art-key count is compared and not just the size and
+the index.
+
+Three things in that check are load-bearing and easy to undo by accident. It
+arms at queue index **one** rather than wherever the walk left off, which buys
+a row on either side (`prev()` seeks to zero at the top of a queue and
+`next()` stops at the end), a track that has just started (`prev()` is a seek
+again past five seconds), and the fact that while the queue index is at most
+ten nothing is clamped off the front of the window — so the window's index IS
+the queue index, which is what lets the logged index be compared against the
+queue's directly. It requires each reading to be a FRESH one at both ends, the
+push counter up and a new line in the log, because a `prev()` that lands back
+on the row it started from reads exactly like a stale line otherwise. And it
+FAILS rather than skips when it cannot be armed — a queue under three rows, or
+repeat-one, under which `next()` seeks instead of stepping — with the reason
+in the message.
+
 ## What a screen reader says
 
 Every control on the phone is named by what it does, in the app's own
@@ -1851,12 +1895,13 @@ read over real IPC; a cold artist page, its ⋯, the whole-discography page and
 its A–Z; the first-run preview with `setupWrites` at 0; eleven raw backend
 strings through `__ss.say`; and a refused transfer's sentence.
 
-Then, after the step loop, seven things the mock cannot do at all: a
+Then, after the step loop, eight things the mock cannot do at all: a
 force-stop and the paused restore that follows it (waited out past the
 thirteen-second FGS-kill window), the position restored, playback resumed, the
 system media session and its ownership, media keys, ten seconds in the
-background with the position still advancing, and SoulStream's own mixer
-underruns.
+background with the position still advancing, SoulStream's own mixer
+underruns, and the queue window that rides along with every card update and
+that nothing on the card reads.
 
 One block in the phone walk pulls bytes, and only when the app is signed in:
 the trailing network block types `--query` into Search, streams a peer's copy