yellowjacket/.planning/plans/pending/016-android-feature-parity.md

016 — What Android parity would actually take

Status: A1, A2 and A3 are done (commit "let the app reach the user's music"). The direction taken is option 1, the full librarian: MANAGE_EXTERNAL_STORAGE plus an in-app folder browser, which keeps the path-keyed model intact. A4 (MediaSession and audio focus) and B1/B2 remain. The sections below are kept as written, because they are the argument the decision rests on — see "What is left" at the end for the current state.

Plan 015 shipped a pipeline: the app cross-compiles, is signed and versioned, and publishes from CI. This is the assessment of what stands between that and an Android app worth installing.

The headline: parity is the wrong target, and choosing it would be the expensive mistake. Four of the blockers below are not porting work — they are the Android platform declining to support the model this app is built on. The decision to make first is in "The fork in the road" at the end; everything before it is evidence for that decision.

Severity is what the app does today, verified against the source and the generated manifest, not guessed.

A. It cannot work at all until these are fixed

A1. The app can read no music. (deepest)

build/android/app/src/main/AndroidManifest.xml requests INTERNET, VIBRATE, ACCESS_NETWORK_STATE, USE_BIOMETRIC, POST_NOTIFICATIONS, the two location permissions, CAMERA and the two FOREGROUND_SERVICE ones. There is no storage or media permission of any kind. At targetSdk 35 that means the app can see its own private directory and nothing else.

Adding READ_MEDIA_AUDIO is necessary and not sufficient, because it grants access through MediaStore, not through the filesystem. This app's entire model is absolute paths: audio_files.file_path is the primary key of ownership, AddLibrary(path) takes a directory, the scanner walks it with os.ReadDir, and every one of GetFilePathsByAlbums / ByGenres / ByRecordingMBIDs exists to hand paths to the player. Scoped storage does not offer a stable directory to walk.

The honest options are three, and they are not close in cost:

• MediaStore as the library source. Query the content resolver, keep MediaStore IDs (or content URIs) beside or instead of paths, and open audio through a ContentResolver file descriptor. This is the Android-native answer and it touches the schema, the scanner, the player's file opening and every path-keyed query.
• MANAGE_EXTERNAL_STORAGE. Keeps the path model intact and is effectively barred from Google Play except for genuine file managers. Viable only because we distribute through Obtainium — which is a real point in its favour here, and worth stating plainly rather than dismissing.
• App-private storage only, i.e. the user copies music into the app's sandbox. Trivial to build, and nobody wants it.

A2. The first-run flow cannot complete.

first-run-wizard.ts calls DirectoryPicker(), which is frontendutil.DirectoryPicker → app.Dialog.OpenFile(). CanChooseDirectories(true). Wails' own ANDROID.md lists open-directory dialogs as "❌ Returns an error — SAF yields tree URIs, not filesystem paths". So the one action the wizard exists to perform fails, and <first-run-wizard> intercepts all pointer events until a library exists — so the app is not merely empty, it is inert.

Whatever A1 resolves to decides this: a MediaStore library needs no picker at all, and a SAF tree needs the picker to return a URI the backend can use.

A3. MPRIS is compiled into the Android build.

mpris_linux.go is //go:build linux, and android implies linux (documented, and the reason it is in the APK). It will look for a session bus that does not exist. It needs //go:build linux && !android, and its Android counterpart is A4.

This one is cheap and should be done regardless — it is a two-character build-tag change plus whatever mediacontrols.New returns instead.

A4. Playback will be killed the moment the screen locks.

The scaffold's WailsForegroundService is typed dataSync (foregroundServiceType="dataSync", FOREGROUND_SERVICE_TYPE_DATA_SYNC), and the manifest requests FOREGROUND_SERVICE_DATA_SYNC. A music player needs mediaPlayback and FOREGROUND_SERVICE_MEDIA_PLAYBACK, plus a MediaSession for lock-screen and notification transport controls, plus audio focus — pause on a phone call, duck for a notification, pause on headphone unplug. None of that exists today. oto will happily keep writing to a stream nobody can hear.

This is the difference between "an app that plays audio" and "a music player", and it is Java-side work in the scaffold plus a Go-side bridge.

B. It works, but wrongly

B1. The x86_64 half of the APK cannot run on any Android.

Established in plan 015: modernc.org/libc's Xlstat64 issues a raw lstat on linux/amd64, which Android's seccomp forbids, so the process takes SIGSYS the first time it touches the database. arm64 is structurally unaffected (no lstat syscall exists; it routes through fstatat).

So ~31 MB of the artifact is dead weight on every Android device, including x86 Chromebooks. Options: drop x86_64 from abiFilters (smaller APK, no emulator target — which does not work anyway), or carry it against a future modernc fix. Dropping it is the honest default; it is also the only item in this plan that is a five-minute change.

B2. The UI is a desktop shell.

MinWidth/MinHeight are 800×600 and were measured — below ~780 the header subtitle wraps the title out of its bar. A phone is ~360–430 CSS px wide. The sidebar collapses to icons below 900px, which is a laptop-sized breakpoint, not a phone one. Beyond width: the app is built on hover (the marquee's hover mode, tooltips), right-click context menus, a keyboard shortcut layer with its own overlay and settings page, multi-select with ctrl/shift, and a resizable-column track list. None of those are gestures.

This is not a stylesheet pass. It is a second front end for the views worth having on a phone, sharing the stores and bindings — which the architecture supports, since a view is already a lazily-loaded chunk behind VIEW_LOADERS.

B3. Tag writing cannot reach the user's files.

tagwriter rewrites tags in place, and autotag's whole purpose is applying them to a folder. Under scoped storage that is impossible outside the sandbox without a SAF write grant per tree. If A1 lands on MediaStore, in-place tag writing needs MediaStore write requests and user confirmation per file on Android 11+.

Autotagging is arguably a desktop-only feature and saying so is a legitimate answer.

B4. The Explore catalog is a ~0.6 GB download into app-private storage.

It works — but with no awareness of a metered connection and no accounting for a device where that is a meaningful fraction of free space. At minimum it needs to be opt-in on mobile and to refuse a metered network by default. Android.NetworkJSON() reports {connected,type}, so the signal is available.

C. Inert, and fine

Window geometry, menus and the system tray are documented no-ops on mobile. The keyboard shortcut layer is harmless but its Settings page is dead weight. profiling is already compiled out of production builds. These cost nothing and need no work.

D. Unknown until it runs on a device

Nothing in section A or B has been observed on Android, because the x86_64 emulator cannot run the app (B1) and emulator 37 refuses arm64 images on an x86_64 host. Everything above is read from the source, the generated manifest and Wails' own documentation. The first real device run will find things this list does not have, and the most likely places are audio latency and buffering under oto/oboe, and SQLite behaviour on app-private storage.

The fork in the road

The four blockers in section A are all the same question wearing different clothes: is the Android app a librarian, or a player?

YellowJacket on the desktop is a librarian. It scans folders, deduplicates covers, detects duplicate tracks, reconciles against MusicBrainz, rewrites tags on disk, and manages downloads. That model rests on owning a filesystem, which is precisely what Android declines to give.

Three coherent products, and only the first is "parity":

1. Full librarian on Android. Requires MANAGE_EXTERNAL_STORAGE (Obtainium-only distribution, which we already have), a phone UI for every view, and media-session playback. Largest scope by far; the result is an app almost nobody has asked for on a phone.
2. A player for music already on the phone. MediaStore as the source, no scanner, no autotag, no downloads; the library, queue, playlists, favourites and Explore-as-browsing all still make sense. This is a genuinely good Android app and it is not parity — it is a subset with a different data source.
3. A companion to the desktop app. The phone browses and controls the desktop's library over the network, or syncs a subset. Smallest Android surface, and it leans on the thing that already works.

Option 2 is the recommendation if the goal is an app people use; option 3 if the goal is the least work for the most value. Option 1 is the only one that answers "feature parity" literally, and it is the one worth arguing hardest against.

What is worth doing regardless of that decision

Cheap, independently useful, and each unblocks measurement:

1. Drop x86_64 from abiFilters (B1) — or keep it and document why. Five minutes.
2. //go:build linux && !android on mpris_linux.go (A3), so the Android build stops carrying a D-Bus client. Small.
3. A device smoke run, which needs someone's phone and the published APK. Everything in D depends on it, and it is the single highest information-per-minute action available.
4. Make the first-run wizard fail legibly rather than inertly (A2) — the picker's error already routes through describeError, but the wizard still blocks pointer events, so an Android user sees a dead screen rather than a sentence. Even under option 3 this is the right behaviour.

What is left (updated after A1-A3)

A4, playback that survives the screen locking. The manifest and the service are typed mediaPlayback now and the permission is declared, so the foundation is in place; what is missing is a MediaSession, a transport notification and audio-focus handling. The plumbing for it exists and needs no new JNI: Go can call application.Android.StartForegroundService(json) (exported by Wails), and Java can call WailsBridge.emitEvent(name, json) back into the application event bus, which Go subscribes to. So the shape is a JSON payload of title/artist/state going out and transport commands coming back, with backend/mediacontrols gaining an Android handler beside the MPRIS one — the interface it already defines is the right shape.

Audio focus is the half that is easy to forget and the more important one: pause on a phone call, duck for a notification, pause on headphone unplug. oto will happily keep writing to a stream nobody can hear.

B1, the x86_64 half of the APK, which cannot run on any Android because of the modernc lstat seccomp trap. Still undecided; dropping it is a five-minute change that halves the artifact.

B2, the desktop shell. Untouched and the largest remaining piece.

B3/B4 are unchanged, and B3 is now possible where it was not: with all-files access, tagwriter can write in place.

What A1-A3 did not answer

Nothing here has been observed on a device. The permission flow in particular is the kind of thing that behaves differently across OEM builds — ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION is implemented inconsistently, which is why there is a fallback to the global list, and neither path has been exercised.