Amber/CLAUDE.md

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Build & development commands

./gradlew assembleDebug          # debug build
./gradlew assembleRelease        # release build (requires signing keystore)
./gradlew ktlintCheck            # Kotlin style check (also runs on every git commit via pre-commit hook)
./gradlew ktlintFormat           # auto-fix Kotlin style issues
./gradlew lint                   # Android Lint, warnings fail the build (runs on commit and push via hooks)
./gradlew test --no-daemon       # unit tests (also runs on every git push via pre-push hook)
./build.sh                       # builds both offline and free release variants to ~/release/

Git hooks are auto-installed via the root build.gradle.kts preBuild task — no manual setup needed.

Build flavors

Flavor	Purpose
free (default)	Online variant with full networking (OkHttp, Coil, relay connectivity)
offline	No network stack; use BuildFlavorChecker.isOfflineFlavor() to guard network code

Modules

• :app — the Android app (everything below in Architecture refers to it)
• :desktop — Compose for Desktop (JVM) NIP-46 signer for Windows/macOS/Linux; standalone port that mirrors the Android permission model against quartz-jvm (no NIP-55). ./gradlew :desktop:run to launch, :desktop:packageDistributionForCurrentOs to package. Its core mirrors NotificationSubscription/EventNotificationConsumer/BunkerRequestUtils in desktop/.../core/BunkerEngine.kt — behavior changes to the Android bunker flow should be ported there too. Keys are AES-encrypted via a PKCS12 Java KeyStore (DesktopKeyStore) whose password lives in the OS credential store (Keychain / Credential Manager / Secret Service via java-keyring, file fallback — see KeystorePassword.resolve); an opt-in PassphraseLock instead wraps the master key with Argon2id and adds a startup/auto-lock gate that evicts key material and gates the bunker engine — and, while set, encrypts the per-account database (apps/permissions/history/logs) at rest via writeSecure/readSecure. State is JSON files per account (no Room). See desktop/README.md.

Architecture

Request ingestion — three paths

External apps and relays reach the signer through three distinct paths:

1. nostrsigner:// Intent → SignerActivity → parsed by IntentUtils → shown as bottom sheet
2. ContentProvider IPC → SignerProvider → synchronous signing via runBlocking
3. NIP-46 relay events (kind 24133) → NotificationSubscription → EventNotificationConsumer → BunkerRequestUtils

All three paths converge on Account.sign() / encrypt/decrypt methods backed by NostrSignerInternal.

Global state — Amber.kt

Amber is the Application class and acts as the DI container. Key singletons it owns:

• applicationIOScope — CoroutineScope(Dispatchers.IO + SupervisorJob() + exceptionHandler), used for all background work
• client: NostrClient — the Quartz Nostr relay client
• notificationSubscription — keeps the NIP-46 filter alive in the background
• profileSubscription — per-account, throttled one-shot metadata fetch; first fetches the user's NIP-65 relay list (kind 10002) and saves it locally, then fetches the metadata (kind 0) from the default profile relays plus the saved user relays; started/stopped by the composables that display each account via ProfileSubscriptionEffect (not app-wide)
• isStartingAppState: MutableStateFlow<Boolean> — set to true during runMigrations(); code that must wait for startup calls isStartingAppState.first { !it }
• settings.killSwitch — when true, all relays are disconnected; checked before every relay operation

Per-account isolation

Every npub gets its own:

• SharedPreferences file (prefs_${npub})
• AppDatabase (amber_db_${npub}) — apps + permissions
• LogDatabase — operation logs
• HistoryDatabase — request history

All databases are lazy-loaded and cached in ConcurrentHashMaps in Amber. Account data (including decrypted keys) is loaded via LocalPreferences.loadFromEncryptedStorage() and cached in LargeCache.

Permission system

Permissions are stored in ApplicationEntity + ApplicationPermissionsEntity (Room). Each permission entry has:

• rememberType — auto-accept, auto-reject, or always-ask
• acceptUntil / rejectUntil — time-bound grants
• kind — event-kind-specific rules

Before showing the approval UI, all three ingestion paths query the database; if a matching auto-accept rule exists, signing proceeds silently.

Biometric / PIN lock is UI-only

The biometric/PIN prompt (useAuth / usePin in AmberSettings, configured in SecurityScreen) is only an app-launch UI gate, not a signing gate. It is rendered by BiometricAuthScreen, which is invoked exclusively from the two UI entry points — MainActivity and SignerActivity — to unlock the app's screens before any approval bottom sheet is shown.

It does not protect the signing operations themselves:

• ContentProvider IPC (SignerProvider) and NIP-46 relay events (EventNotificationConsumer → BunkerRequestUtils) never touch BiometricAuthScreen, Biometrics, useAuth, or usePin. They sign in the background based purely on the permission database.
• When an auto-accept rule matches, all three paths sign silently without triggering the biometric/PIN prompt — including nostrsigner:// intents, which auto-finish before the UI is interacted with.

In other words, the lock controls who can open and navigate the app UI; it does not stand between a request and Account.sign(). Authorization for automatic signing is governed solely by the permission system (rememberType / acceptUntil / kind).

Key files

File	Purpose
Amber.kt	Application singleton, Nostr client, relay connectivity
LocalPreferences.kt	Account/settings persistence, encrypted key storage
IntentUtils.kt	Parses nostrsigner:// URIs, creates IntentData objects
SignerProvider.kt	ContentProvider IPC signing
BunkerRequestUtils.kt	NIP-46 protocol handling, relay responses
AccountStateViewModel.kt	Auth state, account switching, toast notifications
ConnectivityService.kt	Foreground service, network monitoring, relay reconnection
BiometricAuthScreen.kt	UI-only app-launch lock (biometric/PIN); not a signing gate
Biometrics.kt	Wraps BiometricPrompt / keyguard credential prompt
SecurityScreen.kt	Toggles useAuth / usePin and the re-prompt interval

• For repository collaboration, use ngit and follow .claude/skills/ngit/SKILL.md.