subtracks/AGENTS.md

AGENTS.md

Guidance for agents (and humans) working in this repository.

What this is

A native Android rewrite of Subtracks, a client for Subsonic-compatible servers (Navidrome, gonic, Airsonic, ...), in Kotlin and Jetpack Compose. The main history still contains the earlier Flutter app; the native app is being built fresh under app/ and ships as com.subtracks. The aim is a clean, F-Droid-friendly client: free/libre dependencies only, no telemetry.

Environment

Everything comes from the Nix flake devshell; do not install toolchains by hand.

• Enter it with nix develop, or let direnv load it into your shell (.envrc runs use flake).
• The default devshell provides JDK 21, Gradle 9, the Android SDK (platform 37, build-tools 37.0.0, platform-tools 37.0.1) and nushell.
• The integration harness needs real servers, so it lives in a separate nix develop .#integration shell (navidrome, gonic, lms, php, Nextcloud with the Music app, sqlite). Keeping them out of the default shell avoids pulling that closure into everyday builds.
• Build with the devshell gradle, not ./gradlew. CI uses the nix Gradle pinned by flake.lock; the wrapper is kept only for people without Nix.

Commands

• Build: gradle :app:assembleDebug
• Release build: gradle :app:assembleRelease only when build config, R8/ProGuard or dependencies change, and once before a merge; not part of routine verification
• Unit tests: gradle :app:testDebugUnitTest
• Lint: gradle :app:ktlintCheck :app:lintDebug
• Format: gradle :app:ktlintFormat
• Integration tests: nix develop .#integration --command nu tools/integration-test.nu (starts navidrome, gonic, lms and a Nextcloud Music instance, then runs :app:integrationTest)
• Screenshots: gradle :app:recordRoborazziDebug renders the *Screen composables to app/src/test/screenshots/ (gitignored) plus an HTML report in app/build/reports/roborazzi/, for local review. No golden images are committed and verifyRoborazziDebug is not part of CI.
• Demo screenshots: gradle :app:demoScreenshots does a real sync of the public Navidrome demo (https://demo.navidrome.org, demo/demo) and renders the store screenshots with that library's art and names into app/src/test/screenshots/demo/ (gitignored). Needs network; not part of CI or the integration suite.

Testing layout

• app/src/test - JVM unit tests (JUnit4, Robolectric, Roborazzi, MockWebServer). Run by :app:testDebugUnitTest.
• app/src/integrationTest - tests that need real servers. Compiled with the unit test sources but run by the dedicated :app:integrationTest task, and excluded from every *UnitTest task. The nushell harness starts the servers for you.
• A test earns its place only if it fails when the behaviour it covers breaks, and passes when the behaviour works. A test that passes either way is worse than no test: it looks like coverage while hiding the gap. So when you add one, break the behaviour (or run the test against the pre-fix code), watch it fail, then restore the fix and watch it pass.

CI

• Forgejo Actions, .forgejo/workflows/ci.yml, a single ci job that runs the lint, unit test and integration test steps (one cache restore/save and Gradle warm-up instead of three).
• Runs on the nix-docker runner (the localhost/nix-ci image built by the separate nix-home repo) inside the devshell, restoring the Nix store via cache-nix-action and caching Gradle and the integration test music.
• The nix-docker and bookworm runner labels, their images and the runner's networking are defined in the separate nix-home repo (hosts-incus/git-runner.nix).
• Pull requests from a fork need approval before the workflow runs.
• The GitHub mirror and the GitHub PR import live under .forgejo/; see .forgejo/README.md.

Conventions

• Prefer self-explanatory code; do not add comments unless the reason cannot be inferred from the code itself (docstrings for functions and exports are fine).
• ktlint (org.jlleitschuh.gradle.ktlint) enforces style and flags unused imports; run gradle :app:ktlintFormat before committing. .editorconfig exempts @Composable functions from the lowerCamelCase function-naming rule.
• Room 3 (androidx.room3) on AndroidX sqlite-bundled (BundledSQLiteDriver, SQLite 3.50+). Do not reintroduce SQLDelight or the platform SQLite.
• Networking uses OkHttp and DOM XML parsing; auth uses the Subsonic token scheme by default.
• Use coroutines and Flow; library reads are exposed as Flow from Room. Large lists page with Paging 3 over Room PagingSource rather than loading the whole table.
• The library is mirrored in full at sync and must work offline. Never fetch library metadata on demand for browsing, filtering or sorting; only media bytes (streams, downloads) and images are on-demand. A server-derived sort key must be synced into a local column, not requested lazily when the sort is selected.
• Playback is Media3: PlaybackService is a MediaSessionService owning an ExoPlayer, and PlaybackController (app-scoped Koin singleton) is the only thing the UI talks to. The queue is a queue_entries list of references with optional ranges plus a playback_cursor row; keep only a bounded window in memory (never the whole queue, and never load a whole table to build one). Stream URLs are freshly salted per request, so attach artwork by CoverArtRef cache key, not by URL.
• UI state lives in androidx.lifecycle.ViewModel, wired with Koin (koinViewModel()); screens split into a stateful *Route and a stateless *Screen for screenshot tests.
• UI and playback preferences go in DataStore (UserPreferences), not Room.
• Verify current dependency versions and their compatibility before adding or pinning anything.

Gotchas

• Robolectric runs at SDK 35 while targetSdk is 37; raising it changes the on-demand Roborazzi renders (there are no committed goldens to re-record).
• Room 3 does not map PagingSource automatically: a DAO that returns it needs @DaoReturnTypeConverters(PagingSourceDaoReturnTypeConverter::class).
• Material icons are not pulled in by material3; use the BOM-managed material-icons-core/material-icons-extended (frozen at 1.7.8). Extended is large in debug builds but R8 strips unused icons from release.
• Robolectric creates a fresh Application per test in one JVM, so SubtracksApp.onCreate stops any running Koin before startKoin.
• The CI image provides nix-ld, jq, sqlite, node, zstd and a runner user that cache-nix-action expects. None of that is needed locally beyond the devshell.
• Integration servers: navidrome on 4533 (admin/password), gonic on 4747 (admin/admin), lms on 5082 (admin/subtracks-lms), Nextcloud Music on 8090 (admin/subtracks-nextcloud, base URL http://localhost:8090/index.php/apps/music/subsonic/). The test music is cached in .integration/music (gitignored).
• lms and Nextcloud Music authenticate the Subsonic API with per-user API keys instead of passwords. The harness seeds a key and most tests use useTokenAuth = false; SubsonicAuthIntegrationTest drives useTokenAuth = true and asserts the fallback to plaintext (lms answers code 42, Nextcloud 41).
• nix develop does not source your shell rc files (so tools like atuin are not active); use direnv if you want your normal interactive shell.
• The store screenshots in metadata/en-US/images/phoneScreenshots/ must be 24-bit no-alpha PNGs (Play rejects palette and alpha PNGs for screenshots); re-encode after regenerating, e.g. magick in.png -strip -type TrueColor PNG24:out.png.