Sync a compact local catalog and surface available updates.

.gitignore

@@ -1,6 +1,7 @@
 # Project-specific
 reference/
 .android-sdk/
+src/main/assets/catalog.db
 
 # OS
 .DS_Store

Makefile

@@ -9,16 +9,62 @@ AVD_HOME ?= $(HOME)/.android/avd
 AVD_CONFIG ?= $(AVD_HOME)/$(AVD_NAME).avd/config.ini
 PACKAGE ?= dev.zapstore.beta
 ACTIVITY ?= dev.zapstore.app.MainActivity
+KEYSTORE ?= release.keystore
+KEYSTORE_PASSWORD ?=
+KEY_ALIAS ?=
+KEY_PASSWORD ?= $(KEYSTORE_PASSWORD)
+DEBUG_KEYSTORE ?= $(HOME)/.android/debug.keystore
 
-.PHONY: build install run deploy refresh emulator
+ZSP_CATALOG_DB ?= ../zsp/testdata/catalog/catalog.db
+ASSETS_CATALOG_DB := src/main/assets/catalog.db
+
+.PHONY: build release install run deploy refresh emulator bundle-catalog
+
+bundle-catalog: $(ASSETS_CATALOG_DB)
+
+$(ASSETS_CATALOG_DB): $(ZSP_CATALOG_DB)
+	@mkdir -p src/main/assets
+	cp "$(ZSP_CATALOG_DB)" "$@"
 
 build:
 	$(GRADLE) assembleDebug
 
+release:
+	@if [ -f "$(KEYSTORE)" ]; then \
+		store="$(abspath $(KEYSTORE))"; \
+		pass="$(KEYSTORE_PASSWORD)"; \
+		alias="$(KEY_ALIAS)"; \
+		keypass="$(KEY_PASSWORD)"; \
+		if [ -z "$$pass" ] || [ -z "$$alias" ]; then \
+			echo "Found $$store; set KEYSTORE_PASSWORD and KEY_ALIAS to sign the release build."; \
+			exit 1; \
+		fi; \
+	else \
+		echo "No $(KEYSTORE); signing release with the Android debug certificate"; \
+		store="$(DEBUG_KEYSTORE)"; \
+		if [ ! -f "$$store" ]; then \
+			mkdir -p "$$(dirname "$$store")"; \
+			keytool -genkeypair -keystore "$$store" \
+				-storepass android -keypass android \
+				-alias androiddebugkey -keyalg RSA -keysize 2048 -validity 10000 \
+				-dname "CN=Android Debug,O=Android,C=US"; \
+		fi; \
+		pass=android; \
+		alias=androiddebugkey; \
+		keypass=android; \
+	fi; \
+	$(GRADLE) assembleRelease \
+		-Pandroid.injected.signing.store.file="$$store" \
+		-Pandroid.injected.signing.store.password="$$pass" \
+		-Pandroid.injected.signing.key.alias="$$alias" \
+		-Pandroid.injected.signing.key.password="$$keypass"
+
 install:
 	$(GRADLE) installDebug
 
 run: install
+	@$(ADB) reverse tcp:3334 tcp:3334 || true
+	@$(ADB) reverse tcp:3336 tcp:3336 || true
 	@$(ADB) shell am force-stop $(PACKAGE)
 	@$(ADB) shell am start -n $(PACKAGE)/$(ACTIVITY)
 	@if [ -t 0 ]; then \

build.gradle.kts

@@ -44,9 +44,13 @@ dependencies {
     implementation(libs.coil.compose)
     implementation(libs.coil.network.okhttp)
     implementation(libs.okhttp)
+    implementation(libs.sqlite)
+    implementation(libs.sqlite.bundled)
 
     testImplementation(libs.junit)
     testImplementation(libs.coroutines.test)
+    testImplementation(libs.okhttp.mockwebserver)
+    testImplementation(libs.sqlite.bundled)
 
     androidTestImplementation(platform(libs.compose.bom))
     androidTestImplementation(libs.androidx.test.junit)

gradle/libs.versions.toml

@@ -5,6 +5,7 @@ quartz = "1.13.1"
 coroutines = "1.11.0"
 coil = "3.5.0"
 okhttp = "5.4.0"
+sqlite = "2.6.2"
 compose-bom = "2026.05.01"
 activity = "1.13.0"
 lifecycle = "2.11.0"
@@ -20,6 +21,9 @@ coil = { module = "io.coil-kt.coil3:coil", version.ref = "coil" }
 coil-compose = { module = "io.coil-kt.coil3:coil-compose", version.ref = "coil" }
 coil-network-okhttp = { module = "io.coil-kt.coil3:coil-network-okhttp", version.ref = "coil" }
 okhttp = { module = "com.squareup.okhttp3:okhttp", version.ref = "okhttp" }
+okhttp-mockwebserver = { module = "com.squareup.okhttp3:mockwebserver", version.ref = "okhttp" }
+sqlite = { module = "androidx.sqlite:sqlite", version.ref = "sqlite" }
+sqlite-bundled = { module = "androidx.sqlite:sqlite-bundled", version.ref = "sqlite" }
 compose-bom = { module = "androidx.compose:compose-bom", version.ref = "compose-bom" }
 compose-foundation = { module = "androidx.compose.foundation:foundation" }
 compose-material-icons-extended = { module = "androidx.compose.material:material-icons-extended" }

iolite/src/main/kotlin/dev/zapstore/iolite/Iolite.kt

@@ -173,6 +173,16 @@ class Iolite private constructor(
         reconnectWithoutBackoff()
     }
 
+    /**
+     * Reloads every active local projection from the store. Use after a catalog
+     * delta or snapshot commits so screens see the new epoch without thousands
+     * of per-row store-change events.
+     */
+    fun invalidateLocalProjections() {
+        if (closed.get()) return
+        synchronized(sessionsLock) { sessions.toList() }.forEach(QuerySession::reseedLocal)
+    }
+
     /**
      * Enables or suspends all relay traffic for app foreground/background.
      * Suspending closes every relay socket and stops the keep-alive reconnector;
@@ -354,6 +364,12 @@ class Iolite private constructor(
             }
         }
 
+        fun reseedLocal() {
+            if (stopped.get() || options.sourceMode == SourceMode.Remote) return
+            observerJob?.cancel()
+            observerJob = startObserver(initialPhase = { lastState.phase })
+        }
+
         private fun startLocalOnly() {
             observerJob = startObserver(initialPhase = { QueryPhase.LocalOnly })
         }
@@ -937,6 +953,7 @@ class Iolite private constructor(
             websocketBuilder: WebsocketBuilder,
             parentScope: CoroutineScope,
             config: IoliteConfig = IoliteConfig(),
+            eventStore: (path: String) -> IEventStore = { path -> EventStore(dbName = path, relay = null) },
         ): Iolite {
             config.validate()
             val parentJob = requireActiveParentJob(parentScope)
@@ -953,7 +970,7 @@ class Iolite private constructor(
             var store: ObservableEventStore? = null
             var client: INostrClient? = null
             try {
-                store = ObservableEventStore(EventStore(dbName = path, relay = null))
+                store = ObservableEventStore(eventStore(path))
                 val refreshCache = SharedPreferencesQueryRefreshCache.create(
                     context = appContext,
                     databasePath = path,
@@ -983,8 +1000,8 @@ class Iolite private constructor(
         }
 
         /**
-         * Test-only construction seam. It is internal so consumers cannot replace the
-         * canonical Quartz-backed store or client in production.
+         * Test construction seam. Production code should pass [eventStore] to [create]
+         * instead of calling this.
          */
         internal fun createForTesting(
             eventStore: IEventStore,

src/androidTest/kotlin/dev/zapstore/app/ScreensTest.kt

@@ -21,7 +21,7 @@ class ScreensTest {
     fun homeSearchAndStackCallbacksAreWired() {
         var submitted = false
         var cleared = false
-        var notificationsOpened = false
+        var updatesOpened = false
         var openedStack: String? = null
         val stack = StackInfo(
             event(
@@ -42,7 +42,7 @@ class ScreensTest {
                     onSearchQueryChanged = {},
                     onSearchSubmitted = { submitted = true },
                     onSearchCleared = { cleared = true },
-                    onNotificationsClick = { notificationsOpened = true },
+                    onUpdatesClick = { updatesOpened = true },
                     onStackClick = { openedStack = it },
                     onAppClick = { _, _ -> },
                 )
@@ -52,12 +52,12 @@ class ScreensTest {
         composeRule.onNodeWithTag("searchField").performImeAction()
         composeRule.onNodeWithText("×").performClick()
         composeRule.onNodeWithTag("searchField").assertIsFocused()
-        composeRule.onNodeWithTag("notificationsButton").performClick()
+        composeRule.onNodeWithTag("updatesButton").performClick()
         composeRule.onNodeWithTag("stack:stack-id").performClick()
 
         assertTrue(submitted)
         assertTrue(cleared)
-        assertTrue(notificationsOpened)
+        assertTrue(updatesOpened)
         assertEquals("stack-id", openedStack)
     }
 

src/main/AndroidManifest.xml

@@ -1,10 +1,12 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android">
     <uses-permission android:name="android.permission.INTERNET" />
+    <uses-permission android:name="android.permission.QUERY_ALL_PACKAGES" />
 
     <application
         android:name=".ZapstoreApplication"
         android:icon="@drawable/ic_launcher"
         android:label="@string/app_name"
+        android:networkSecurityConfig="@xml/network_security_config"
         android:theme="@style/AppTheme">
         <activity
             android:name=".MainActivity"

src/main/kotlin/dev/zapstore/app/Catalog.kt

@@ -5,6 +5,8 @@ import com.vitorpamplona.quartz.nip01Core.core.Event
 import com.vitorpamplona.quartz.nip01Core.relay.filters.Filter
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.normalizeRelayUrl
 import com.vitorpamplona.quartz.nip01Core.relay.sockets.okhttp.BasicOkHttpWebSocket
+import com.vitorpamplona.quartz.nip01Core.store.IEventStore
+import dev.zapstore.app.catalogsync.CatalogSchema
 import dev.zapstore.iolite.OutboxRouter
 import dev.zapstore.iolite.Iolite
 import dev.zapstore.iolite.IoliteConfig
@@ -35,6 +37,10 @@ import kotlin.time.Duration.Companion.seconds
 import kotlin.time.Duration.Companion.days
 
 object Catalog {
+    const val updatesUrl = "http://127.0.0.1:3336"
+    /** Temporary: browse the compact catalog only. Flip false to restore relays. */
+    const val catalogLocalOnly = true
+    const val catalogRelayPubkey = "79be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798"
     const val relay = "wss://relay.zapstore.dev"
     const val profileRelay = "wss://relay.vertexlab.io"
     const val assetKind = 3_063
@@ -61,16 +67,26 @@ internal val PROFILE_CACHE_DURATION = 1.days
 private const val VERIFIED_ASSET_AND_C1_LIMIT = 500
 
 fun catalogQueryOptions(
-    sourceMode: SourceMode = SourceMode.LocalAndRemote,
+    sourceMode: SourceMode = if (Catalog.catalogLocalOnly) SourceMode.Local else SourceMode.LocalAndRemote,
     remoteMode: RemoteMode? = if (sourceMode == SourceMode.Local) null else RemoteMode.OneShot(),
     cachedFor: Duration? = if (sourceMode == SourceMode.LocalAndRemote) DEFAULT_CACHE_DURATION else null,
     relays: Set<String> = setOf(Catalog.relay),
-): QueryOptions = QueryOptions(
+): QueryOptions {
+    if (Catalog.catalogLocalOnly) {
+        return QueryOptions(
+            sourceMode = SourceMode.Local,
+            remoteMode = null,
+            relays = emptySet(),
+            cachedFor = null,
+        )
+    }
+    return QueryOptions(
         sourceMode = sourceMode,
         remoteMode = remoteMode,
         relays = if (sourceMode == SourceMode.Local) emptySet() else relays.map(String::normalizeRelayUrl).toSet(),
         cachedFor = cachedFor,
     )
+}
 
 interface CatalogRepository {
     fun query(
@@ -161,9 +177,14 @@ interface CatalogRepository {
      * Local data remains fully queryable while suspended.
      */
     fun setRelayTrafficEnabled(enabled: Boolean) = Unit
+
+    fun purpleQuartz(): Iolite? = null
 }
 
-class IoliteCatalogRepository(context: Context) : CatalogRepository {
+class IoliteCatalogRepository(
+    context: Context,
+    private val eventStoreFactory: ((String) -> IEventStore)? = null,
+) : CatalogRepository {
     private val applicationContext = context.applicationContext
     private val scope = CoroutineScope(SupervisorJob() + Dispatchers.Main.immediate)
     private val profileFlows = ConcurrentHashMap<String, Flow<ProfileInfo?>>()
@@ -187,10 +208,14 @@ class IoliteCatalogRepository(context: Context) : CatalogRepository {
             BasicOkHttpWebSocket.Builder { OkHttpClient() },
             scope,
             config = IoliteConfig(
+                databaseName = CatalogSchema.DATABASE_NAME,
                 // Zap receipts are the unbounded firehose. Addressable catalog kinds are
                 // bounded by supersession; assets back the release feed and stay.
                 pruneRules = mapOf(Catalog.zapReceiptKind to 90.days),
             ),
+            eventStore = eventStoreFactory ?: { path ->
+                com.vitorpamplona.quartz.nip01Core.store.sqlite.EventStore(dbName = path, relay = null)
+            },
         ).also {
             client = it
             if (!relayTrafficEnabled) it.setRelayTrafficEnabled(false)
@@ -209,7 +234,9 @@ class IoliteCatalogRepository(context: Context) : CatalogRepository {
         relays: Set<String>,
         remoteMode: RemoteMode,
         unionWithFallback: Boolean,
-    ): Flow<QueryState> = router().queryWithOutbox(
+    ): Flow<QueryState> {
+        if (Catalog.catalogLocalOnly) return query(filters, catalogQueryOptions())
+        return router().queryWithOutbox(
             filters,
             authors,
             fallbackRelays = relays.map(String::normalizeRelayUrl).toSet(),
@@ -217,6 +244,7 @@ class IoliteCatalogRepository(context: Context) : CatalogRepository {
             remoteMode = remoteMode,
             unionWithFallback = unionWithFallback,
         )
+    }
 
     override fun profile(pubkey: String): Flow<ProfileInfo?> =
         profileFlows.getOrPut(pubkey) {
@@ -253,6 +281,8 @@ class IoliteCatalogRepository(context: Context) : CatalogRepository {
         client?.setRelayTrafficEnabled(enabled)
     }
 
+    override fun purpleQuartz(): Iolite? = client()
+
     private suspend fun resolveC1Author(app: AppInfo): String? {
         return query(
             listOf(
@@ -378,8 +408,21 @@ data class ReleaseInfo(val event: Event) {
                 ?.takeIf(String::isNotBlank)
     val version: String get() = event.tagValue("version") ?: "Unknown version"
     val channel: String? get() = event.tagValue("c")
+        ?: "main".takeIf { event.kind == Catalog.assetKind }
     val notes: String get() = event.content
+
+    fun outranks(other: ReleaseInfo): Boolean {
+        if (version == other.version && event.kind != other.event.kind) {
+            return event.kind == Catalog.releaseKind
         }
+        if (event.createdAt != other.event.createdAt) return event.createdAt > other.event.createdAt
+        if (event.kind != other.event.kind) return event.kind == Catalog.releaseKind
+        return event.id < other.event.id
+    }
+}
+
+fun preferredRelease(current: ReleaseInfo?, candidate: ReleaseInfo): ReleaseInfo =
+    if (current == null || candidate.outranks(current)) candidate else current
 
 data class StackInfo(val event: Event) {
     val identifier: String get() = event.tagValue("d") ?: event.id

src/main/kotlin/dev/zapstore/app/MainActivity.kt

@@ -25,8 +25,10 @@ import androidx.navigation.compose.rememberNavController
 import androidx.navigation.navArgument
 
 class MainActivity : ComponentActivity() {
+    private val zapstore: ZapstoreApplication
+        get() = getApplication() as ZapstoreApplication
     private val repository: CatalogRepository
-        get() = (application as ZapstoreApplication).catalogRepository
+        get() = zapstore.catalogRepository
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
@@ -74,15 +76,19 @@ class MainActivity : ComponentActivity() {
                                 factory = homeViewModelFactory(repository),
                             )
                             val state by viewModel.uiState.collectAsStateWithLifecycle()
+                            val syncState by zapstore.catalogSyncRepository.state.collectAsStateWithLifecycle()
                             HomeScreen(
                                 state = state,
                                 repository = repository,
                                 onSearchQueryChanged = viewModel::onSearchQueryChanged,
                                 onSearchSubmitted = viewModel::submitSearch,
                                 onSearchCleared = viewModel::clearSearch,
-                                onNotificationsClick = {
-                                    navController.navigate(NOTIFICATIONS_ROUTE)
+                                onUpdatesClick = {
+                                    navController.navigate(UPDATES_ROUTE)
                                 },
+                                updateCount = syncState.availableUpdates.size,
+                                databaseRowCount = syncState.eventRowCount,
+                                catalogError = syncState.error,
                                 onLoadMoreReleases = viewModel::loadMoreReleases,
                                 onStackClick = { stackId ->
                                     navController.navigate(stackRoute(stackId))
@@ -96,8 +102,18 @@ class MainActivity : ComponentActivity() {
                             )
                         }
 
-                        composable(NOTIFICATIONS_ROUTE) {
-                            NotificationsScreen()
+                        composable(UPDATES_ROUTE) {
+                            val viewModel: UpdatesViewModel = viewModel(
+                                factory = updatesViewModelFactory(zapstore.catalogSyncRepository),
+                            )
+                            val state by viewModel.uiState.collectAsStateWithLifecycle()
+                            UpdatesScreen(
+                                state = state,
+                                onSync = viewModel::sync,
+                                onAppClick = { identifier, author ->
+                                    navController.navigate(appRoute(identifier, author))
+                                },
+                            )
                         }
 
                         composable(
@@ -200,7 +216,7 @@ private const val STACK_ROUTE = "stack/{$STACK_ID_ARGUMENT}"
 private const val APP_ROUTE =
     "app/{$APP_IDENTIFIER_ARGUMENT}?$APP_AUTHOR_ARGUMENT={$APP_AUTHOR_ARGUMENT}"
 private const val PROFILE_ROUTE = "profile/{$PROFILE_PUBKEY_ARGUMENT}"
-private const val NOTIFICATIONS_ROUTE = "notifications"
+private const val UPDATES_ROUTE = "updates"
 private const val NAVIGATION_TRANSITION_DURATION = 150
 
 private fun stackRoute(stackId: String): String =

src/main/kotlin/dev/zapstore/app/ViewModels.kt

@@ -227,10 +227,7 @@ private class ReleaseFeedLoader(
                         val identifier = release.appIdentifier ?: return@forEach
                         val address = "${Catalog.appKind}:${release.event.pubKey}:$identifier"
                         if (address in appsByAddress) {
-                            val existing = releasesByApp[address]
-                            if (existing == null || existing.event.createdAt < release.event.createdAt) {
-                                releasesByApp[address] = release
-                            }
+                            releasesByApp[address] = preferredRelease(releasesByApp[address], release)
                         }
                     }
                 publishEntries()
@@ -396,6 +393,7 @@ class HomeViewModel(
 data class StackDetailUiState(
     val stack: StackInfo? = null,
     val appsByAddress: Map<String, AppInfo> = emptyMap(),
+    val releasesByAddress: Map<String, ReleaseInfo> = emptyMap(),
     val stackLoading: Boolean = true,
     val appsLoading: Boolean = false,
     val error: String? = null,
@@ -410,7 +408,9 @@ class StackDetailViewModel(
     val uiState: StateFlow<StackDetailUiState> = _uiState.asStateFlow()
 
     private var appsJob: Job? = null
+    private var releasesJob: Job? = null
     private var appAddresses: List<String> = emptyList()
+    private var releaseLookupKeys: Set<String> = emptySet()
 
     init {
         viewModelScope.launch {
@@ -435,13 +435,19 @@ class StackDetailViewModel(
         if (addresses == appAddresses) return
         appAddresses = addresses
         appsJob?.cancel()
+        releasesJob?.cancel()
+        releaseLookupKeys = emptySet()
         val coordinates = addresses.mapNotNull(String::toAppCoordinate)
         if (coordinates.isEmpty()) {
-            _uiState.update { it.copy(appsByAddress = emptyMap(), appsLoading = false) }
+            _uiState.update {
+                it.copy(appsByAddress = emptyMap(), releasesByAddress = emptyMap(), appsLoading = false)
+            }
             return
         }
 
-        _uiState.update { it.copy(appsByAddress = emptyMap(), appsLoading = true) }
+        _uiState.update {
+            it.copy(appsByAddress = emptyMap(), releasesByAddress = emptyMap(), appsLoading = true)
+        }
         appsJob = viewModelScope.launch {
             repository.query(
                 Filter(
@@ -459,6 +465,40 @@ class StackDetailViewModel(
                         error = state.error?.message ?: it.error,
                     )
                 }
+                observeReleases(apps)
+            }
+        }
+    }
+
+    private fun observeReleases(apps: List<AppInfo>) {
+        val lookupKeys = apps.map(AppInfo::address).toSet()
+        if (lookupKeys == releaseLookupKeys) return
+        releaseLookupKeys = lookupKeys
+        releasesJob?.cancel()
+        if (apps.isEmpty()) {
+            _uiState.update { it.copy(releasesByAddress = emptyMap()) }
+            return
+        }
+        val releaseFilters = apps.map { app ->
+            Filter(
+                authors = listOf(app.event.pubKey),
+                kinds = Catalog.releaseKinds,
+                tags = mapOf("i" to listOf(app.identifier)),
+                limit = 1,
+            )
+        }
+        releasesJob = viewModelScope.launch {
+            repository.query(releaseFilters).collect { queryState ->
+                val releases = linkedMapOf<String, ReleaseInfo>()
+                queryState.items
+                    .filter { it.kind in Catalog.releaseKinds }
+                    .map(::ReleaseInfo)
+                    .forEach { release ->
+                        val identifier = release.appIdentifier ?: return@forEach
+                        val address = "${Catalog.appKind}:${release.event.pubKey}:$identifier"
+                        releases[address] = preferredRelease(releases[address], release)
+                    }
+                _uiState.update { it.copy(releasesByAddress = releases) }
             }
         }
     }
@@ -667,12 +707,16 @@ class AppDetailViewModel(
         viewModelScope.launch {
             repository.query(
                 Filter(
-                    kinds = listOf(Catalog.releaseKind),
+                    authors = author?.let(::listOf),
+                    kinds = Catalog.releaseKinds,
                     tags = mapOf("i" to listOf(identifier)),
                     limit = 10,
                 ),
             ).collect { state ->
-                val release = state.items.map(::ReleaseInfo).maxByOrNull { it.event.createdAt }
+                val release = state.items
+                    .filter { it.kind in Catalog.releaseKinds }
+                    .map(::ReleaseInfo)
+                    .reduceOrNull(::preferredRelease)
                 _uiState.update {
                     it.copy(
                         release = release,
@@ -691,10 +735,30 @@ class AppDetailViewModel(
     }
 }
 
+class UpdatesViewModel(
+    private val catalogSync: dev.zapstore.app.catalogsync.CatalogSyncRepository,
+) : ViewModel() {
+    val uiState = catalogSync.state
+
+    init {
+        catalogSync.refreshUpdates()
+    }
+
+    fun sync() {
+        viewModelScope.launch { catalogSync.sync() }
+    }
+}
+
 fun homeViewModelFactory(repository: CatalogRepository): ViewModelProvider.Factory = viewModelFactory {
     initializer { HomeViewModel(repository, createSavedStateHandle()) }
 }
 
+fun updatesViewModelFactory(
+    catalogSync: dev.zapstore.app.catalogsync.CatalogSyncRepository,
+): ViewModelProvider.Factory = viewModelFactory {
+    initializer { UpdatesViewModel(catalogSync) }
+}
+
 fun stackDetailViewModelFactory(repository: CatalogRepository): ViewModelProvider.Factory = viewModelFactory {
     initializer { StackDetailViewModel(repository, createSavedStateHandle()) }
 }

src/main/kotlin/dev/zapstore/app/ZapstoreApplication.kt

@@ -4,16 +4,44 @@ import android.app.Application
 import androidx.lifecycle.DefaultLifecycleObserver
 import androidx.lifecycle.LifecycleOwner
 import androidx.lifecycle.ProcessLifecycleOwner
+import dev.zapstore.app.catalogsync.CatalogBootstrapper
+import dev.zapstore.app.catalogsync.CatalogSyncClient
+import dev.zapstore.app.catalogsync.CatalogSyncRepository
+import dev.zapstore.app.catalogsync.CompactEventStore
+import dev.zapstore.app.catalogsync.InstalledAppsProvider
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.launch
 
 class ZapstoreApplication : Application() {
+    private val applicationScope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
+
+    val catalogDatabase by lazy { CatalogBootstrapper(this).open() }
+    val compactStore by lazy { CompactEventStore(catalogDatabase) }
     val catalogRepository: CatalogRepository by lazy {
-        IoliteCatalogRepository(this)
+        IoliteCatalogRepository(this) { compactStore }
+    }
+    val catalogSyncRepository by lazy {
+        CatalogSyncRepository(
+            database = catalogDatabase,
+            store = compactStore,
+            client = CatalogSyncClient(Catalog.updatesUrl),
+            installedApps = { InstalledAppsProvider(this).installedApps() },
+            trustedPubkey = Catalog.catalogRelayPubkey,
+            purpleQuartz = { catalogRepository.purpleQuartz() },
+        )
     }
 
     override fun onCreate() {
         super.onCreate()
         ProcessLifecycleOwner.get().lifecycle.addObserver(object : DefaultLifecycleObserver {
-            override fun onStart(owner: LifecycleOwner) = catalogRepository.setRelayTrafficEnabled(true)
+            override fun onStart(owner: LifecycleOwner) {
+                if (!Catalog.catalogLocalOnly) {
+                    catalogRepository.setRelayTrafficEnabled(true)
+                }
+                applicationScope.launch { catalogSyncRepository.sync() }
+            }
             override fun onStop(owner: LifecycleOwner) = catalogRepository.setRelayTrafficEnabled(false)
         })
     }

src/main/kotlin/dev/zapstore/app/catalogsync/CatalogBootstrapper.kt

@@ -0,0 +1,49 @@
+package dev.zapstore.app.catalogsync
+
+import android.content.Context
+import java.io.File
+
+class CatalogBootstrapper(
+    private val context: Context,
+    private val databaseName: String = CatalogSchema.DATABASE_NAME,
+    private val bundledAsset: String = CatalogSchema.BUNDLED_ASSET,
+) {
+    fun open(): ZapstoreDatabase {
+        val target = context.getDatabasePath(databaseName)
+        if (!target.exists()) {
+            copyBundled(target)
+        }
+        return if (target.exists()) {
+            val database = ZapstoreDatabase.open(target.absolutePath)
+            if (database.catalogState() == null) {
+                database.writeCatalogState(emptyState())
+            }
+            database
+        } else {
+            ZapstoreDatabase.createEmpty(target.absolutePath)
+        }
+    }
+
+    private fun copyBundled(target: File) {
+        val copied = runCatching {
+            context.assets.open(bundledAsset).use { input ->
+                target.parentFile?.mkdirs()
+                val temp = File(target.parentFile, "${target.name}.copy")
+                temp.outputStream().use { input.copyTo(it) }
+                if (!temp.renameTo(target)) {
+                    temp.copyTo(target, overwrite = true)
+                    temp.delete()
+                }
+            }
+        }
+        copied.exceptionOrNull()
+    }
+
+    private fun emptyState() = CatalogState(
+        catalog = CatalogSchema.CATALOG,
+        epoch = 0,
+        schemaVersion = CatalogSchema.VERSION,
+        searchModel = CatalogSchema.SEARCH_MODEL,
+        generation = 0,
+    )
+}

src/main/kotlin/dev/zapstore/app/catalogsync/CatalogEnvelope.kt

@@ -0,0 +1,208 @@
+package dev.zapstore.app.catalogsync
+
+import com.vitorpamplona.quartz.nip01Core.core.Event
+import org.json.JSONArray
+import org.json.JSONObject
+import java.io.ByteArrayInputStream
+import java.io.ByteArrayOutputStream
+import java.io.File
+import java.io.InputStream
+import java.nio.ByteBuffer
+import java.nio.ByteOrder
+import java.util.zip.GZIPInputStream
+import java.util.zip.GZIPOutputStream
+
+data class CatalogManifest(
+    val event: Event,
+    val contentHash: String,
+    val oldEpoch: Long,
+    val newEpoch: Long,
+    val schemaVersion: Int,
+    val searchModel: String,
+    val catalog: String,
+    val kind: String,
+)
+
+data class CatalogDelta(
+    val events: List<Event>,
+    val deletedIds: List<String>,
+    val oldEpoch: Long,
+    val newEpoch: Long,
+)
+
+data class DecodedEnvelope(
+    val manifest: CatalogManifest,
+    val payload: ByteArray,
+)
+
+object CatalogEnvelope {
+    fun encode(manifestEventJson: String, payload: ByteArray): ByteArray {
+        val compressed = gzip(payload)
+        val manifestBytes = manifestEventJson.toByteArray(Charsets.UTF_8)
+        val buffer = ByteBuffer.allocate(CatalogSchema.MAGIC.size + 4 + manifestBytes.size + compressed.size)
+            .order(ByteOrder.BIG_ENDIAN)
+        buffer.put(CatalogSchema.MAGIC)
+        buffer.putInt(manifestBytes.size)
+        buffer.put(manifestBytes)
+        buffer.put(compressed)
+        return buffer.array()
+    }
+
+    fun decode(bytes: ByteArray): DecodedEnvelope {
+        require(bytes.size >= CatalogSchema.MAGIC.size + 4) { "catalog envelope is truncated" }
+        val buffer = ByteBuffer.wrap(bytes).order(ByteOrder.BIG_ENDIAN)
+        val magic = ByteArray(CatalogSchema.MAGIC.size)
+        buffer.get(magic)
+        require(magic.contentEquals(CatalogSchema.MAGIC)) { "catalog envelope magic is invalid" }
+        val manifestLength = buffer.int
+        require(manifestLength > 0 && manifestLength <= buffer.remaining()) { "catalog envelope manifest is truncated" }
+        val manifestBytes = ByteArray(manifestLength)
+        buffer.get(manifestBytes)
+        val compressed = ByteArray(buffer.remaining())
+        buffer.get(compressed)
+        return DecodedEnvelope(
+            manifest = parseManifest(JSONObject(String(manifestBytes, Charsets.UTF_8))),
+            payload = gunzip(compressed),
+        )
+    }
+
+    fun decodeStreamToFile(input: InputStream, payloadFile: File): CatalogManifest {
+        val magic = input.readExact(CatalogSchema.MAGIC.size)
+        require(magic.size == CatalogSchema.MAGIC.size && magic.contentEquals(CatalogSchema.MAGIC)) {
+            "catalog envelope magic is invalid"
+        }
+        val lengthBytes = input.readExact(4)
+        require(lengthBytes.size == 4) { "catalog envelope is truncated" }
+        val manifestLength = ByteBuffer.wrap(lengthBytes).order(ByteOrder.BIG_ENDIAN).int
+        require(manifestLength > 0) { "catalog envelope manifest is truncated" }
+        val manifestBytes = input.readExact(manifestLength)
+        require(manifestBytes.size == manifestLength) { "catalog envelope manifest is truncated" }
+        payloadFile.outputStream().use { output ->
+            GZIPInputStream(input).use { gzip -> gzip.copyTo(output) }
+        }
+        return parseManifest(JSONObject(String(manifestBytes, Charsets.UTF_8)))
+    }
+
+    private fun InputStream.readExact(count: Int): ByteArray {
+        val bytes = ByteArray(count)
+        var offset = 0
+        while (offset < count) {
+            val read = read(bytes, offset, count - offset)
+            if (read < 0) return bytes.copyOf(offset)
+            offset += read
+        }
+        return bytes
+    }
+
+    fun parseManifest(json: JSONObject): CatalogManifest {
+        val event = Event(
+            id = json.getString("id"),
+            pubKey = json.getString("pubkey"),
+            createdAt = json.getLong("created_at"),
+            kind = json.getInt("kind"),
+            tags = decodeEventTags(json.getJSONArray("tags")),
+            content = json.getString("content"),
+            sig = json.getString("sig"),
+        )
+        val body = JSONObject(event.content)
+        return CatalogManifest(
+            event = event,
+            contentHash = body.getString("content_hash"),
+            oldEpoch = body.getLong("old_epoch"),
+            newEpoch = body.getLong("new_epoch"),
+            schemaVersion = body.getInt("schema_version"),
+            searchModel = body.getString("search_model"),
+            catalog = body.optString("catalog", CatalogSchema.CATALOG),
+            kind = body.getString("kind"),
+        )
+    }
+
+    fun parseDelta(payload: ByteArray): CatalogDelta {
+        val json = JSONObject(String(payload, Charsets.UTF_8))
+        val events = json.getJSONArray("events")
+        val deleted = json.optJSONArray("deleted_ids") ?: JSONArray()
+        return CatalogDelta(
+            events = List(events.length()) { parseWireEvent(events.getJSONObject(it)) },
+            deletedIds = List(deleted.length()) { deleted.getString(it) },
+            oldEpoch = json.getLong("old_epoch"),
+            newEpoch = json.getLong("new_epoch"),
+        )
+    }
+
+    fun encodeDelta(delta: CatalogDelta): ByteArray {
+        val events = JSONArray()
+        delta.events.forEach { events.put(wireEvent(it)) }
+        val deleted = JSONArray()
+        delta.deletedIds.forEach(deleted::put)
+        return JSONObject()
+            .put("events", events)
+            .put("deleted_ids", deleted)
+            .put("old_epoch", delta.oldEpoch)
+            .put("new_epoch", delta.newEpoch)
+            .toString()
+            .toByteArray(Charsets.UTF_8)
+    }
+
+    fun parseWireEvent(json: JSONObject): Event = Event(
+        id = json.getString("id"),
+        pubKey = json.getString("pubkey"),
+        createdAt = json.getLong("created_at"),
+        kind = json.getInt("kind"),
+        tags = decodeEventTags(json.getJSONArray("tags")),
+        content = json.getString("content"),
+        sig = json.getString("sig"),
+    )
+
+    fun wireEvent(event: Event): JSONObject = JSONObject()
+        .put("id", event.id)
+        .put("pubkey", event.pubKey)
+        .put("created_at", event.createdAt)
+        .put("kind", event.kind)
+        .put("tags", JSONArray(event.tags.map { JSONArray(it.toList()) }))
+        .put("content", event.content)
+        .put("sig", event.sig)
+
+    fun decodeEventTags(tags: JSONArray): Array<Array<String>> =
+        Array(tags.length()) { index ->
+            val row = tags.getJSONArray(index)
+            Array(row.length()) { row.getString(it) }
+        }
+
+    fun gzip(bytes: ByteArray): ByteArray {
+        val output = ByteArrayOutputStream()
+        GZIPOutputStream(output).use { it.write(bytes) }
+        return output.toByteArray()
+    }
+
+    fun gunzip(bytes: ByteArray): ByteArray =
+        GZIPInputStream(ByteArrayInputStream(bytes)).use { it.readBytes() }
+}
+
+data class UpdatesRequest(
+    val protocol: Int,
+    val catalog: String,
+    val schemaVersion: Int,
+    val epoch: Long,
+    val searchModel: String,
+) {
+    fun toJson(): String =
+        """{"protocol":$protocol,"catalog":"$catalog","schema_version":$schemaVersion,"epoch":$epoch,"search_model":"$searchModel"}"""
+
+    fun forbiddenFields(): Set<String> = emptySet()
+}
+
+fun parseUpdatesRequest(json: JSONObject): UpdatesRequest {
+    val forbidden = listOf(
+        "installed", "apps", "package", "packages", "search", "query", "hashes", "versions",
+    )
+    json.keys().asSequence().forEach { key ->
+        require(key !in forbidden) { "updates request must not include $key" }
+    }
+    return UpdatesRequest(
+        protocol = json.getInt("protocol"),
+        catalog = json.getString("catalog"),
+        schemaVersion = json.getInt("schema_version"),
+        epoch = json.getLong("epoch"),
+        searchModel = json.getString("search_model"),
+    )
+}

src/main/kotlin/dev/zapstore/app/catalogsync/CatalogSchema.kt

@@ -0,0 +1,84 @@
+package dev.zapstore.app.catalogsync
+
+object CatalogSchema {
+    const val VERSION = 1
+    const val PROTOCOL = 1
+    const val CATALOG = "default"
+    const val SEARCH_MODEL = "leaf-ir-v1"
+    const val DATABASE_NAME = "zapstore.db"
+    const val BUNDLED_ASSET = "catalog.db"
+    const val MANIFEST_KIND = 30_078
+    const val CONTENT_TYPE_DELTA = "application/vnd.zapstore.catalog-delta"
+    val MAGIC = byteArrayOf('Z'.code.toByte(), 'S'.code.toByte(), 'C'.code.toByte(), '1'.code.toByte())
+
+    val CREATE_STATEMENTS = listOf(
+        """
+        CREATE TABLE IF NOT EXISTS events (
+            id BLOB PRIMARY KEY,
+            pubkey BLOB NOT NULL,
+            created_at INTEGER NOT NULL,
+            kind INTEGER NOT NULL,
+            d_tag TEXT NOT NULL DEFAULT '',
+            content TEXT NOT NULL,
+            tags TEXT NOT NULL
+        )
+        """.trimIndent(),
+        "CREATE INDEX IF NOT EXISTS events_kind_time ON events(kind, created_at DESC, id)",
+        "CREATE INDEX IF NOT EXISTS events_pubkey_kind_time ON events(pubkey, kind, created_at DESC, id)",
+        "CREATE INDEX IF NOT EXISTS events_kind_d ON events(kind, pubkey, d_tag)",
+        """
+        CREATE TABLE IF NOT EXISTS event_tags (
+            event_id BLOB NOT NULL,
+            key TEXT NOT NULL,
+            value TEXT NOT NULL,
+            PRIMARY KEY (key, value, event_id),
+            FOREIGN KEY (event_id) REFERENCES events(id) ON DELETE CASCADE
+        )
+        """.trimIndent(),
+        "CREATE INDEX IF NOT EXISTS event_tags_event ON event_tags(event_id)",
+        """
+        CREATE TABLE IF NOT EXISTS catalog_state (
+            catalog TEXT PRIMARY KEY,
+            epoch INTEGER NOT NULL,
+            schema_version INTEGER NOT NULL,
+            search_model TEXT NOT NULL,
+            generation INTEGER NOT NULL DEFAULT 0
+        )
+        """.trimIndent(),
+        """
+        CREATE TABLE IF NOT EXISTS apps (
+            app_id TEXT PRIMARY KEY,
+            event_id BLOB NOT NULL,
+            pubkey BLOB NOT NULL,
+            name TEXT NOT NULL,
+            created_at INTEGER NOT NULL
+        )
+        """.trimIndent(),
+        """
+        CREATE TABLE IF NOT EXISTS releases (
+            app_id TEXT NOT NULL,
+            version TEXT NOT NULL,
+            event_id BLOB NOT NULL,
+            channel TEXT,
+            created_at INTEGER NOT NULL,
+            PRIMARY KEY (app_id, version)
+        )
+        """.trimIndent(),
+        """
+        CREATE TABLE IF NOT EXISTS assets (
+            event_id BLOB PRIMARY KEY,
+            app_id TEXT NOT NULL,
+            version_code INTEGER,
+            version TEXT,
+            mime TEXT,
+            platform TEXT,
+            variant TEXT,
+            certificate_hash TEXT,
+            file_hash TEXT,
+            url TEXT,
+            created_at INTEGER NOT NULL
+        )
+        """.trimIndent(),
+        "CREATE INDEX IF NOT EXISTS assets_app ON assets(app_id, version_code)",
+    )
+}

src/main/kotlin/dev/zapstore/app/catalogsync/CatalogSyncClient.kt

@@ -0,0 +1,48 @@
+package dev.zapstore.app.catalogsync
+
+import okhttp3.MediaType.Companion.toMediaType
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import okhttp3.RequestBody.Companion.toRequestBody
+import java.util.concurrent.TimeUnit
+
+sealed class UpdatesResponse {
+    data class Delta(val body: ByteArray) : UpdatesResponse()
+    data object NotModified : UpdatesResponse()
+    data class Error(val status: Int, val code: String?, val reason: String?) : UpdatesResponse()
+}
+
+class CatalogSyncClient(
+    private val baseUrl: String,
+    private val http: OkHttpClient = OkHttpClient.Builder()
+        .connectTimeout(30, TimeUnit.SECONDS)
+        .readTimeout(120, TimeUnit.SECONDS)
+        .followRedirects(false)
+        .followSslRedirects(false)
+        .build(),
+) {
+    fun requestUpdates(request: UpdatesRequest): UpdatesResponse {
+        val call = http.newCall(
+            Request.Builder()
+                .url(baseUrl.trimEnd('/') + "/updates")
+                .header("Content-Type", "application/json")
+                .post(request.toJson().toRequestBody(JSON_MEDIA))
+                .build(),
+        )
+        call.execute().use { response ->
+            return when (response.code) {
+                200 -> UpdatesResponse.Delta(response.body.bytes())
+                304 -> UpdatesResponse.NotModified
+                else -> UpdatesResponse.Error(
+                    status = response.code,
+                    code = response.header("X-Error-Code"),
+                    reason = response.header("X-Reason"),
+                )
+            }
+        }
+    }
+
+    companion object {
+        private val JSON_MEDIA = "application/json; charset=utf-8".toMediaType()
+    }
+}

src/main/kotlin/dev/zapstore/app/catalogsync/CatalogSyncRepository.kt

@@ -0,0 +1,145 @@
+package dev.zapstore.app.catalogsync
+
+import dev.zapstore.iolite.Iolite
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
+
+data class CatalogSyncUiState(
+    val epoch: Long = 0,
+    val eventRowCount: Long = 0,
+    val lastSyncedAtMillis: Long? = null,
+    val syncing: Boolean = false,
+    val error: String? = null,
+    val availableUpdates: List<AvailableUpdate> = emptyList(),
+)
+
+class CatalogSyncRepository(
+    private val database: ZapstoreDatabase,
+    private val store: CompactEventStore,
+    private val client: CatalogSyncClient,
+    private val installedApps: () -> List<InstalledApp>,
+    private val trustedPubkey: String,
+    private val purpleQuartz: () -> Iolite?,
+    private val now: () -> Long = { System.currentTimeMillis() },
+) {
+    private val mutex = Mutex()
+    private val _state = MutableStateFlow(
+        CatalogSyncUiState(
+            epoch = database.catalogState()?.epoch ?: 0,
+            eventRowCount = database.eventRowCount(),
+            availableUpdates = currentUpdates(),
+        ),
+    )
+    val state: StateFlow<CatalogSyncUiState> = _state.asStateFlow()
+
+    fun refreshUpdates() {
+        _state.value = _state.value.copy(availableUpdates = currentUpdates())
+    }
+
+    suspend fun sync() {
+        mutex.withLock {
+            _state.value = _state.value.copy(syncing = true, error = null)
+            try {
+                applyRemoteUpdate()
+                _state.value = readUiState(lastSyncedAtMillis = now(), error = null)
+                purpleQuartz()?.invalidateLocalProjections()
+            } catch (failure: Throwable) {
+                _state.value = readUiState(
+                    lastSyncedAtMillis = _state.value.lastSyncedAtMillis,
+                    error = failure.message ?: failure::class.simpleName,
+                )
+            }
+        }
+    }
+
+    private fun applyRemoteUpdate() {
+        val current = database.catalogState() ?: error("catalog state is missing")
+        val request = UpdatesRequest(
+            protocol = CatalogSchema.PROTOCOL,
+            catalog = current.catalog,
+            schemaVersion = current.schemaVersion,
+            epoch = current.epoch,
+            searchModel = current.searchModel,
+        )
+        when (val response = client.requestUpdates(request)) {
+            UpdatesResponse.NotModified -> Unit
+            is UpdatesResponse.Delta -> applyDelta(response.body, current)
+            is UpdatesResponse.Error -> throw CatalogVerificationException(
+                response.reason ?: "catalog update failed with HTTP ${response.status}",
+            )
+        }
+    }
+
+    private fun applyDelta(body: ByteArray, current: CatalogState) {
+        val envelope = CatalogEnvelope.decode(body)
+        CatalogVerifier.verifyEnvelope(
+            envelope,
+            trustedPubkey = trustedPubkey,
+            expectedKind = "delta",
+            expectedOldEpoch = current.epoch,
+            schemaVersion = current.schemaVersion,
+            searchModel = current.searchModel,
+            catalog = current.catalog,
+        )
+        val delta = CatalogEnvelope.parseDelta(envelope.payload)
+        delta.events.forEach(CatalogVerifier::verifyEvent)
+        store.applyDelta(
+            events = delta.events,
+            deletedIds = delta.deletedIds,
+            next = current.copy(
+                epoch = delta.newEpoch,
+                generation = current.generation + 1,
+            ),
+        )
+    }
+
+    private fun readUiState(
+        lastSyncedAtMillis: Long? = _state.value.lastSyncedAtMillis,
+        error: String? = _state.value.error,
+    ) = CatalogSyncUiState(
+        epoch = database.catalogState()?.epoch ?: 0,
+        eventRowCount = database.eventRowCount(),
+        lastSyncedAtMillis = lastSyncedAtMillis,
+        syncing = false,
+        error = error,
+        availableUpdates = currentUpdates(),
+    )
+
+    private fun currentUpdates(): List<AvailableUpdate> =
+        LocalUpdateMatcher.match(installedApps(), catalogAssets())
+
+    fun catalogAssets(): List<CatalogAssetRow> = database.withConnection { connection ->
+        connection.prepare(
+            """
+            SELECT assets.app_id, COALESCE(apps.name, assets.app_id), COALESCE(assets.version, ''),
+                   COALESCE(assets.version_code, 0), releases.channel, assets.platform, assets.variant,
+                   assets.certificate_hash, assets.mime
+            FROM assets
+            LEFT JOIN apps ON apps.app_id = assets.app_id
+            LEFT JOIN releases ON releases.app_id = assets.app_id AND releases.version = assets.version
+            """.trimIndent(),
+        ).use { statement ->
+            val rows = mutableListOf<CatalogAssetRow>()
+            while (statement.step()) {
+                rows += CatalogAssetRow(
+                    appId = statement.getText(0),
+                    name = statement.getText(1),
+                    version = statement.getText(2),
+                    versionCode = statement.getLong(3),
+                    channel = statement.nullableText(4),
+                    platform = statement.nullableText(5),
+                    variant = statement.nullableText(6),
+                    certificateHash = statement.nullableText(7),
+                    mime = statement.nullableText(8),
+                )
+            }
+            rows
+        }
+    }
+
+    private fun androidx.sqlite.SQLiteStatement.nullableText(index: Int): String? =
+        if (isNull(index)) null else getText(index)
+}

src/main/kotlin/dev/zapstore/app/catalogsync/CatalogVerifier.kt

@@ -0,0 +1,102 @@
+package dev.zapstore.app.catalogsync
+
+import com.vitorpamplona.quartz.nip01Core.crypto.verifyId
+import com.vitorpamplona.quartz.nip01Core.crypto.verifySignature
+import java.io.File
+import java.security.MessageDigest
+
+class CatalogVerificationException(message: String) : Exception(message)
+
+object CatalogVerifier {
+    fun verifyEnvelope(
+        envelope: DecodedEnvelope,
+        trustedPubkey: String,
+        expectedKind: String? = null,
+        expectedOldEpoch: Long? = null,
+        schemaVersion: Int = CatalogSchema.VERSION,
+        searchModel: String = CatalogSchema.SEARCH_MODEL,
+        catalog: String = CatalogSchema.CATALOG,
+    ): CatalogManifest {
+        val manifest = verifyManifest(
+            envelope.manifest,
+            trustedPubkey = trustedPubkey,
+            expectedKind = expectedKind,
+            expectedOldEpoch = expectedOldEpoch,
+            schemaVersion = schemaVersion,
+            searchModel = searchModel,
+            catalog = catalog,
+        )
+        verifyPayloadHash(manifest, envelope.payload)
+        return manifest
+    }
+
+    fun verifyManifest(
+        manifest: CatalogManifest,
+        trustedPubkey: String,
+        expectedKind: String? = null,
+        expectedOldEpoch: Long? = null,
+        schemaVersion: Int = CatalogSchema.VERSION,
+        searchModel: String = CatalogSchema.SEARCH_MODEL,
+        catalog: String = CatalogSchema.CATALOG,
+    ): CatalogManifest {
+        if (manifest.event.kind != CatalogSchema.MANIFEST_KIND) {
+            throw CatalogVerificationException("manifest kind is not a catalog manifest")
+        }
+        if (manifest.event.pubKey != trustedPubkey) {
+            throw CatalogVerificationException("manifest signer is not the configured catalog key")
+        }
+        if (!manifest.event.verifyId() || !manifest.event.verifySignature()) {
+            throw CatalogVerificationException("manifest signature is invalid")
+        }
+        if (manifest.catalog != catalog) {
+            throw CatalogVerificationException("manifest catalog does not match")
+        }
+        if (manifest.schemaVersion != schemaVersion) {
+            throw CatalogVerificationException("manifest schema is incompatible")
+        }
+        if (manifest.searchModel != searchModel) {
+            throw CatalogVerificationException("manifest search model is incompatible")
+        }
+        if (expectedKind != null && manifest.kind != expectedKind) {
+            throw CatalogVerificationException("manifest kind is ${manifest.kind}, expected $expectedKind")
+        }
+        if (expectedOldEpoch != null && manifest.oldEpoch != expectedOldEpoch) {
+            throw CatalogVerificationException("manifest epoch does not continue the local catalog")
+        }
+        return manifest
+    }
+
+    fun verifyPayloadHash(manifest: CatalogManifest, payload: ByteArray) {
+        if (sha256Hex(payload) != manifest.contentHash) {
+            throw CatalogVerificationException("payload hash does not match the manifest")
+        }
+    }
+
+    fun verifyPayloadHash(manifest: CatalogManifest, payload: File) {
+        if (sha256Hex(payload) != manifest.contentHash) {
+            throw CatalogVerificationException("payload hash does not match the manifest")
+        }
+    }
+
+    fun verifyEvent(event: com.vitorpamplona.quartz.nip01Core.core.Event) {
+        if (!event.verifyId() || !event.verifySignature()) {
+            throw CatalogVerificationException("catalog event ${event.id} failed verification")
+        }
+    }
+
+    fun sha256Hex(bytes: ByteArray): String =
+        MessageDigest.getInstance("SHA-256").digest(bytes).toHex()
+
+    fun sha256Hex(file: File): String {
+        val digest = MessageDigest.getInstance("SHA-256")
+        file.inputStream().use { input ->
+            val buffer = ByteArray(DEFAULT_BUFFER_SIZE)
+            while (true) {
+                val read = input.read(buffer)
+                if (read <= 0) break
+                digest.update(buffer, 0, read)
+            }
+        }
+        return digest.digest().toHex()
+    }
+}

src/main/kotlin/dev/zapstore/app/catalogsync/CompactEventStore.kt

@@ -0,0 +1,452 @@
+package dev.zapstore.app.catalogsync
+
+import androidx.sqlite.SQLiteConnection
+import androidx.sqlite.SQLiteStatement
+import com.vitorpamplona.quartz.nip01Core.core.Event
+import com.vitorpamplona.quartz.nip01Core.core.isAddressable
+import com.vitorpamplona.quartz.nip01Core.core.isReplaceable
+import com.vitorpamplona.quartz.nip01Core.relay.filters.Filter
+import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
+import com.vitorpamplona.quartz.nip01Core.store.FtsReindexProgress
+import com.vitorpamplona.quartz.nip01Core.store.IEventStore
+import com.vitorpamplona.quartz.nip40Expiration.isExpired
+import dev.zapstore.app.Catalog
+import org.json.JSONArray
+import java.util.concurrent.atomic.AtomicBoolean
+
+class CompactEventStore(
+    private val database: ZapstoreDatabase,
+) : IEventStore {
+    override val relay: NormalizedRelayUrl? = null
+    private val closed = AtomicBoolean(false)
+
+    override suspend fun insert(event: Event) {
+        database.transaction { insertUnlocked(it, event) }
+    }
+
+    override suspend fun transaction(body: IEventStore.ITransaction.() -> Unit) {
+        database.transaction { connection ->
+            body(object : IEventStore.ITransaction {
+                override fun insert(event: Event) {
+                    insertUnlocked(connection, event)
+                }
+            })
+        }
+    }
+
+    override suspend fun <T : Event> query(filter: Filter): List<T> = query(listOf(filter))
+
+    override suspend fun <T : Event> query(filters: List<Filter>): List<T> {
+        if (filters.isEmpty()) return emptyList()
+        val seen = linkedSetOf<String>()
+        val matches = mutableListOf<T>()
+        database.withConnection { connection ->
+            filters.forEach { filter ->
+                selectCandidates(connection, filter).forEach { event ->
+                    @Suppress("UNCHECKED_CAST")
+                    if (filter.match(event) && seen.add(event.id)) {
+                        matches += event as T
+                    }
+                }
+            }
+        }
+        return matches
+    }
+
+    override suspend fun <T : Event> query(filter: Filter, onEach: (T) -> Unit) {
+        query<T>(filter).forEach(onEach)
+    }
+
+    override suspend fun <T : Event> query(filters: List<Filter>, onEach: (T) -> Unit) {
+        query<T>(filters).forEach(onEach)
+    }
+
+    override suspend fun count(filter: Filter): Int = query<Event>(filter).size
+
+    override suspend fun count(filters: List<Filter>): Int = query<Event>(filters).size
+
+    override suspend fun delete(filter: Filter) {
+        delete(listOf(filter))
+    }
+
+    override suspend fun delete(filters: List<Filter>) {
+        database.transaction { connection ->
+            filters.forEach { filter ->
+                selectCandidates(connection, filter)
+                    .filter(filter::match)
+                    .forEach { deleteEvent(connection, it.id.hexToBytes()) }
+            }
+        }
+    }
+
+    override suspend fun deleteExpiredEvents() {
+        database.transaction { connection ->
+            selectAll(connection)
+                .filter { it.isExpired() }
+                .forEach { deleteEvent(connection, it.id.hexToBytes()) }
+        }
+    }
+
+    override suspend fun reindexFullTextSearch() = Unit
+
+    override suspend fun reindexFullTextSearch(resumeFrom: String?, batchSize: Int): FtsReindexProgress =
+        FtsReindexProgress(cursor = null, processedThisBatch = 0, done = true)
+
+    override fun close() {
+        closed.set(true)
+    }
+
+    fun insertAll(events: List<Event>) {
+        database.transaction { connection ->
+            events.forEach { insertUnlocked(connection, it) }
+        }
+    }
+
+    fun deleteByIds(ids: List<String>) {
+        if (ids.isEmpty()) return
+        database.transaction { connection ->
+            ids.forEach { deleteEvent(connection, it.hexToBytes()) }
+        }
+    }
+
+    fun applyDelta(events: List<Event>, deletedIds: List<String>, next: CatalogState) {
+        database.transaction { connection ->
+            deletedIds.forEach { deleteEvent(connection, it.hexToBytes()) }
+            events.forEach { insertUnlocked(connection, it) }
+            ZapstoreDatabase.upsertCatalogState(connection, next)
+        }
+    }
+
+    private fun insertUnlocked(connection: SQLiteConnection, event: Event) {
+        val id = event.id.hexToBytes()
+        val pubkey = event.pubKey.hexToBytes()
+        val dTag = event.tags.firstOrNull { it.firstOrNull() == "d" }?.getOrNull(1).orEmpty()
+        if (event.kind.isAddressable()) {
+            deleteOlderAddressable(connection, event.kind, pubkey, dTag, event.createdAt, event.id)
+        } else if (event.kind.isReplaceable()) {
+            deleteOlderReplaceable(connection, event.kind, pubkey, event.createdAt, event.id)
+        }
+        connection.prepare(
+            """
+            INSERT OR REPLACE INTO events(id, pubkey, created_at, kind, d_tag, content, tags)
+            VALUES (?, ?, ?, ?, ?, ?, ?)
+            """.trimIndent(),
+        ).use { statement ->
+            statement.bindBlob(1, id)
+            statement.bindBlob(2, pubkey)
+            statement.bindLong(3, event.createdAt)
+            statement.bindLong(4, event.kind.toLong())
+            statement.bindText(5, dTag)
+            statement.bindText(6, event.content)
+            statement.bindText(7, encodeTags(event.tags))
+            statement.step()
+        }
+        connection.prepare("DELETE FROM event_tags WHERE event_id = ?").use { statement ->
+            statement.bindBlob(1, id)
+            statement.step()
+        }
+        event.tags.forEach { tag ->
+            val key = tag.getOrNull(0) ?: return@forEach
+            val value = tag.getOrNull(1) ?: return@forEach
+            connection.prepare("INSERT OR IGNORE INTO event_tags(event_id, key, value) VALUES (?, ?, ?)").use { statement ->
+                statement.bindBlob(1, id)
+                statement.bindText(2, key)
+                statement.bindText(3, value)
+                statement.step()
+            }
+        }
+        upsertDerived(connection, event, id, pubkey)
+    }
+
+    private fun upsertDerived(connection: SQLiteConnection, event: Event, id: ByteArray, pubkey: ByteArray) {
+        when (event.kind) {
+            Catalog.appKind -> {
+                val appId = event.tags.firstOrNull { it.firstOrNull() == "d" }?.getOrNull(1) ?: return
+                val name = event.tags.firstOrNull { it.firstOrNull() == "name" }?.getOrNull(1) ?: appId
+                connection.prepare(
+                    """
+                    INSERT INTO apps(app_id, event_id, pubkey, name, created_at)
+                    VALUES (?, ?, ?, ?, ?)
+                    ON CONFLICT(app_id) DO UPDATE SET
+                        event_id = excluded.event_id,
+                        pubkey = excluded.pubkey,
+                        name = excluded.name,
+                        created_at = excluded.created_at
+                    """.trimIndent(),
+                ).use { statement ->
+                    statement.bindText(1, appId)
+                    statement.bindBlob(2, id)
+                    statement.bindBlob(3, pubkey)
+                    statement.bindText(4, name)
+                    statement.bindLong(5, event.createdAt)
+                    statement.step()
+                }
+            }
+            Catalog.releaseKind -> {
+                val appId = event.tags.firstOrNull { it.firstOrNull() == "i" }?.getOrNull(1)
+                    ?: event.tags.firstOrNull { it.firstOrNull() == "d" }?.getOrNull(1)?.substringBefore('@')
+                    ?: return
+                val version = event.tags.firstOrNull { it.firstOrNull() == "version" }?.getOrNull(1) ?: return
+                val channel = event.tags.firstOrNull { it.firstOrNull() == "c" }?.getOrNull(1)
+                connection.prepare(
+                    """
+                    INSERT INTO releases(app_id, version, event_id, channel, created_at)
+                    VALUES (?, ?, ?, ?, ?)
+                    ON CONFLICT(app_id, version) DO UPDATE SET
+                        event_id = excluded.event_id,
+                        channel = excluded.channel,
+                        created_at = excluded.created_at
+                    """.trimIndent(),
+                ).use { statement ->
+                    statement.bindText(1, appId)
+                    statement.bindText(2, version)
+                    statement.bindBlob(3, id)
+                    if (channel == null) statement.bindNull(4) else statement.bindText(4, channel)
+                    statement.bindLong(5, event.createdAt)
+                    statement.step()
+                }
+            }
+            Catalog.assetKind -> {
+                val appId = event.tags.firstOrNull { it.firstOrNull() == "i" }?.getOrNull(1) ?: return
+                connection.prepare(
+                    """
+                    INSERT INTO assets(
+                        event_id, app_id, version_code, version, mime, platform, variant,
+                        certificate_hash, file_hash, url, created_at
+                    ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+                    ON CONFLICT(event_id) DO UPDATE SET
+                        app_id = excluded.app_id,
+                        version_code = excluded.version_code,
+                        version = excluded.version,
+                        mime = excluded.mime,
+                        platform = excluded.platform,
+                        variant = excluded.variant,
+                        certificate_hash = excluded.certificate_hash,
+                        file_hash = excluded.file_hash,
+                        url = excluded.url,
+                        created_at = excluded.created_at
+                    """.trimIndent(),
+                ).use { statement ->
+                    statement.bindBlob(1, id)
+                    statement.bindText(2, appId)
+                    event.tags.firstOrNull { it.firstOrNull() == "version_code" }?.getOrNull(1)?.toLongOrNull()
+                        ?.let { statement.bindLong(3, it) }
+                        ?: statement.bindNull(3)
+                    bindOptional(statement, 4, event.tag("version"))
+                    bindOptional(statement, 5, event.tag("m"))
+                    bindOptional(statement, 6, event.tags.filter { it.firstOrNull() == "f" }.mapNotNull { it.getOrNull(1) }.joinToString(",").ifEmpty { null })
+                    bindOptional(statement, 7, event.tag("variant"))
+                    bindOptional(statement, 8, event.tag("apk_certificate_hash"))
+                    bindOptional(statement, 9, event.tag("x"))
+                    bindOptional(statement, 10, event.tag("url"))
+                    statement.bindLong(11, event.createdAt)
+                    statement.step()
+                }
+                val version = event.tag("version") ?: return
+                connection.prepare(
+                    """
+                    INSERT INTO releases(app_id, version, event_id, channel, created_at)
+                    VALUES (?, ?, ?, NULL, ?)
+                    ON CONFLICT(app_id, version) DO NOTHING
+                    """.trimIndent(),
+                ).use { statement ->
+                    statement.bindText(1, appId)
+                    statement.bindText(2, version)
+                    statement.bindBlob(3, id)
+                    statement.bindLong(4, event.createdAt)
+                    statement.step()
+                }
+            }
+        }
+    }
+
+    private fun deleteOlderAddressable(
+        connection: SQLiteConnection,
+        kind: Int,
+        pubkey: ByteArray,
+        dTag: String,
+        createdAt: Long,
+        idHex: String,
+    ) {
+        connection.prepare(
+            """
+            SELECT id, created_at FROM events
+            WHERE kind = ? AND pubkey = ? AND d_tag = ?
+            """.trimIndent(),
+        ).use { statement ->
+            statement.bindLong(1, kind.toLong())
+            statement.bindBlob(2, pubkey)
+            statement.bindText(3, dTag)
+            val obsolete = mutableListOf<ByteArray>()
+            while (statement.step()) {
+                val existingId = statement.getBlob(0)
+                val existingCreated = statement.getLong(1)
+                val existingHex = existingId.toHex()
+                if (existingCreated < createdAt || existingCreated == createdAt && existingHex > idHex) {
+                    obsolete += existingId
+                }
+            }
+            obsolete.forEach { deleteEvent(connection, it) }
+        }
+    }
+
+    private fun deleteOlderReplaceable(
+        connection: SQLiteConnection,
+        kind: Int,
+        pubkey: ByteArray,
+        createdAt: Long,
+        idHex: String,
+    ) {
+        connection.prepare("SELECT id, created_at FROM events WHERE kind = ? AND pubkey = ?").use { statement ->
+            statement.bindLong(1, kind.toLong())
+            statement.bindBlob(2, pubkey)
+            val obsolete = mutableListOf<ByteArray>()
+            while (statement.step()) {
+                val existingId = statement.getBlob(0)
+                val existingCreated = statement.getLong(1)
+                val existingHex = existingId.toHex()
+                if (existingCreated < createdAt || existingCreated == createdAt && existingHex > idHex) {
+                    obsolete += existingId
+                }
+            }
+            obsolete.forEach { deleteEvent(connection, it) }
+        }
+    }
+
+    private fun deleteEvent(connection: SQLiteConnection, id: ByteArray) {
+        connection.prepare("DELETE FROM event_tags WHERE event_id = ?").use {
+            it.bindBlob(1, id)
+            it.step()
+        }
+        connection.prepare("DELETE FROM apps WHERE event_id = ?").use {
+            it.bindBlob(1, id)
+            it.step()
+        }
+        connection.prepare("DELETE FROM releases WHERE event_id = ?").use {
+            it.bindBlob(1, id)
+            it.step()
+        }
+        connection.prepare("DELETE FROM assets WHERE event_id = ?").use {
+            it.bindBlob(1, id)
+            it.step()
+        }
+        connection.prepare("DELETE FROM events WHERE id = ?").use {
+            it.bindBlob(1, id)
+            it.step()
+        }
+    }
+
+    private fun selectCandidates(connection: SQLiteConnection, filter: Filter): List<Event> {
+        val clauses = mutableListOf<String>()
+        val binders = mutableListOf<(SQLiteStatement) -> Unit>()
+        var index = 1
+        filter.ids?.takeIf { it.isNotEmpty() }?.let { ids ->
+            clauses += "id IN (${ids.joinToString(",") { "?" }})"
+            ids.forEach { id ->
+                val current = index++
+                binders += { it.bindBlob(current, id.hexToBytes()) }
+            }
+        }
+        filter.authors?.takeIf { it.isNotEmpty() }?.let { authors ->
+            clauses += "pubkey IN (${authors.joinToString(",") { "?" }})"
+            authors.forEach { author ->
+                val current = index++
+                binders += { it.bindBlob(current, author.hexToBytes()) }
+            }
+        }
+        filter.kinds?.takeIf { it.isNotEmpty() }?.let { kinds ->
+            clauses += "kind IN (${kinds.joinToString(",") { "?" }})"
+            kinds.forEach { kind ->
+                val current = index++
+                binders += { it.bindLong(current, kind.toLong()) }
+            }
+        }
+        filter.since?.let { since ->
+            clauses += "created_at >= ?"
+            val current = index++
+            binders += { it.bindLong(current, since) }
+        }
+        filter.until?.let { until ->
+            clauses += "created_at <= ?"
+            val current = index++
+            binders += { it.bindLong(current, until) }
+        }
+        filter.tags?.forEach { (key, values) ->
+            if (values.isEmpty()) return@forEach
+            val placeholders = values.joinToString(",") { "?" }
+            clauses += "id IN (SELECT event_id FROM event_tags WHERE key = ? AND value IN ($placeholders))"
+            val keyIndex = index++
+            binders += { it.bindText(keyIndex, key) }
+            values.forEach { value ->
+                val current = index++
+                binders += { it.bindText(current, value) }
+            }
+        }
+        filter.search?.takeIf { it.isNotBlank() }?.let { search ->
+            clauses += "(content LIKE ? OR id IN (SELECT event_id FROM event_tags WHERE key IN ('name','summary') AND value LIKE ?))"
+            val pattern = "%$search%"
+            val first = index++
+            val second = index++
+            binders += {
+                it.bindText(first, pattern)
+                it.bindText(second, pattern)
+            }
+        }
+        val sql = buildString {
+            append("SELECT id, pubkey, created_at, kind, content, tags FROM events")
+            if (clauses.isNotEmpty()) append(" WHERE ").append(clauses.joinToString(" AND "))
+            append(" ORDER BY created_at DESC, id ASC")
+            filter.limit?.let { append(" LIMIT ").append(it) }
+        }
+        return connection.prepare(sql).use { statement ->
+            binders.forEach { it(statement) }
+            readEvents(statement)
+        }
+    }
+
+    private fun selectAll(connection: SQLiteConnection): List<Event> =
+        connection.prepare("SELECT id, pubkey, created_at, kind, content, tags FROM events").use(::readEvents)
+
+    private fun readEvents(statement: SQLiteStatement): List<Event> {
+        val events = mutableListOf<Event>()
+        while (statement.step()) {
+            events += Event(
+                id = statement.getBlob(0).toHex(),
+                pubKey = statement.getBlob(1).toHex(),
+                createdAt = statement.getLong(2),
+                kind = statement.getInt(3),
+                tags = decodeTags(statement.getText(5)),
+                content = statement.getText(4),
+                sig = "",
+            )
+        }
+        return events
+    }
+
+    private fun Event.tag(name: String): String? =
+        tags.firstOrNull { it.firstOrNull() == name }?.getOrNull(1)
+
+    private fun bindOptional(statement: SQLiteStatement, index: Int, value: String?) {
+        if (value == null) statement.bindNull(index) else statement.bindText(index, value)
+    }
+
+    companion object {
+        fun encodeTags(tags: Array<Array<String>>): String {
+            val array = JSONArray()
+            tags.forEach { tag ->
+                val row = JSONArray()
+                tag.forEach(row::put)
+                array.put(row)
+            }
+            return array.toString()
+        }
+
+        fun decodeTags(raw: String): Array<Array<String>> {
+            val array = JSONArray(raw)
+            return Array(array.length()) { index ->
+                val row = array.getJSONArray(index)
+                Array(row.length()) { row.getString(it) }
+            }
+        }
+    }
+}

src/main/kotlin/dev/zapstore/app/catalogsync/Hex.kt

@@ -0,0 +1,12 @@
+package dev.zapstore.app.catalogsync
+
+internal fun String.hexToBytes(): ByteArray {
+    require(length % 2 == 0) { "hex length must be even" }
+    return ByteArray(length / 2) { index ->
+        substring(index * 2, index * 2 + 2).toInt(16).toByte()
+    }
+}
+
+internal fun ByteArray.toHex(): String = joinToString("") { byte ->
+    (byte.toInt() and 0xff).toString(16).padStart(2, '0')
+}

src/main/kotlin/dev/zapstore/app/catalogsync/InstalledAppsProvider.kt

@@ -0,0 +1,29 @@
+package dev.zapstore.app.catalogsync
+
+import android.content.Context
+import android.content.pm.PackageManager
+import java.security.MessageDigest
+
+class InstalledAppsProvider(
+    private val context: Context,
+) {
+    fun installedApps(): List<InstalledApp> {
+        val manager = context.packageManager
+        return manager.getInstalledPackages(PackageManager.GET_SIGNING_CERTIFICATES).map { info ->
+            val signing = info.signingInfo
+            val certificates = buildSet {
+                signing?.apkContentsSigners?.forEach { add(it.toByteArray().sha256Hex()) }
+                signing?.signingCertificateHistory?.forEach { add(it.toByteArray().sha256Hex()) }
+            }
+            InstalledApp(
+                packageId = info.packageName,
+                versionCode = info.longVersionCode,
+                versionName = info.versionName ?: info.longVersionCode.toString(),
+                certificateHashes = certificates,
+            )
+        }
+    }
+
+    private fun ByteArray.sha256Hex(): String =
+        MessageDigest.getInstance("SHA-256").digest(this).toHex()
+}

src/main/kotlin/dev/zapstore/app/catalogsync/LocalUpdateMatcher.kt

@@ -0,0 +1,80 @@
+package dev.zapstore.app.catalogsync
+
+data class InstalledApp(
+    val packageId: String,
+    val versionCode: Long,
+    val versionName: String,
+    val certificateHashes: Set<String>,
+)
+
+data class CatalogAssetRow(
+    val appId: String,
+    val name: String,
+    val version: String,
+    val versionCode: Long,
+    val channel: String?,
+    val platform: String?,
+    val variant: String?,
+    val certificateHash: String?,
+    val mime: String?,
+)
+
+data class AvailableUpdate(
+    val appId: String,
+    val name: String,
+    val installedVersion: String,
+    val installedVersionCode: Long,
+    val availableVersion: String,
+    val availableVersionCode: Long,
+    val channel: String?,
+)
+
+object LocalUpdateMatcher {
+    fun match(
+        installed: List<InstalledApp>,
+        catalog: List<CatalogAssetRow>,
+        channel: String = "stable",
+        androidPlatforms: Set<String> = ANDROID_PLATFORMS,
+    ): List<AvailableUpdate> {
+        val latestByApp = catalog
+            .filter { row ->
+                (row.channel == null || row.channel == channel) &&
+                    platformMatches(row.platform, androidPlatforms) &&
+                    (row.mime == null || row.mime == ANDROID_MIME)
+            }
+            .groupBy { it.appId }
+            .mapValues { (_, rows) -> rows.maxBy { it.versionCode } }
+        return installed.mapNotNull { app ->
+            val row = latestByApp[app.packageId] ?: return@mapNotNull null
+            if (row.versionCode <= app.versionCode) return@mapNotNull null
+            if (row.certificateHash != null &&
+                row.certificateHash !in app.certificateHashes
+            ) {
+                return@mapNotNull null
+            }
+            AvailableUpdate(
+                appId = app.packageId,
+                name = row.name,
+                installedVersion = app.versionName,
+                installedVersionCode = app.versionCode,
+                availableVersion = row.version,
+                availableVersionCode = row.versionCode,
+                channel = row.channel,
+            )
+        }.sortedBy { it.name.lowercase() }
+    }
+
+    private fun platformMatches(platform: String?, androidPlatforms: Set<String>): Boolean {
+        if (platform.isNullOrBlank()) return true
+        return platform.split(',').any { it in androidPlatforms || it.startsWith("android") }
+    }
+
+    const val ANDROID_MIME = "application/vnd.android.package-archive"
+    val ANDROID_PLATFORMS = setOf(
+        "android-arm64-v8a",
+        "android-armeabi-v7a",
+        "android-x86_64",
+        "android-x86",
+        "android",
+    )
+}

src/main/kotlin/dev/zapstore/app/catalogsync/ZapstoreDatabase.kt

@@ -0,0 +1,149 @@
+package dev.zapstore.app.catalogsync
+
+import androidx.sqlite.SQLiteConnection
+import androidx.sqlite.driver.bundled.BundledSQLiteDriver
+import androidx.sqlite.execSQL
+import java.io.File
+import java.util.concurrent.locks.ReentrantLock
+import kotlin.concurrent.withLock
+
+data class CatalogState(
+    val catalog: String,
+    val epoch: Long,
+    val schemaVersion: Int,
+    val searchModel: String,
+    val generation: Long,
+)
+
+class ZapstoreDatabase private constructor(
+    private val path: String,
+) : AutoCloseable {
+    private val lock = ReentrantLock()
+    private var connection: SQLiteConnection = openConnection(path)
+
+    val file: File get() = File(path)
+
+    fun <T> withConnection(block: (SQLiteConnection) -> T): T = lock.withLock {
+        block(connection)
+    }
+
+    fun transaction(block: (SQLiteConnection) -> Unit) = lock.withLock {
+        connection.execSQL("BEGIN IMMEDIATE")
+        try {
+            block(connection)
+            connection.execSQL("COMMIT")
+        } catch (failure: Throwable) {
+            runCatching { connection.execSQL("ROLLBACK") }
+            throw failure
+        }
+    }
+
+    fun catalogState(catalog: String = CatalogSchema.CATALOG): CatalogState? = withConnection { db ->
+        db.prepare("SELECT catalog, epoch, schema_version, search_model, generation FROM catalog_state WHERE catalog = ?").use { statement ->
+            statement.bindText(1, catalog)
+            if (!statement.step()) return@withConnection null
+            CatalogState(
+                catalog = statement.getText(0),
+                epoch = statement.getLong(1),
+                schemaVersion = statement.getInt(2),
+                searchModel = statement.getText(3),
+                generation = statement.getLong(4),
+            )
+        }
+    }
+
+    fun writeCatalogState(state: CatalogState) = withConnection { db ->
+        upsertCatalogState(db, state)
+    }
+
+    fun eventRowCount(): Long = withConnection { db ->
+        db.prepare("SELECT COUNT(*) FROM events").use { statement ->
+            check(statement.step()) { "event count query returned no row" }
+            statement.getLong(0)
+        }
+    }
+
+    fun pauseAndReplace(snapshot: File) = lock.withLock {
+        connection.close()
+        val target = File(path)
+        val backup = File("$path.bak")
+        if (target.exists()) {
+            backup.delete()
+            if (!target.renameTo(backup)) {
+                connection = openConnection(path)
+                error("could not move the active catalog aside")
+            }
+        }
+        try {
+            if (!snapshot.renameTo(target) && !snapshot.copyTo(target, overwrite = true).exists()) {
+                error("could not install the snapshot")
+            }
+            snapshot.delete()
+            connection = openConnection(path)
+            backup.delete()
+        } catch (failure: Throwable) {
+            if (backup.exists()) {
+                target.delete()
+                backup.renameTo(target)
+            }
+            connection = openConnection(path)
+            throw failure
+        }
+    }
+
+    override fun close() = lock.withLock {
+        connection.close()
+    }
+
+    companion object {
+        fun open(path: String): ZapstoreDatabase {
+            File(path).parentFile?.mkdirs()
+            return ZapstoreDatabase(path).also { it.withConnection(::applySchema) }
+        }
+
+        fun createEmpty(path: String): ZapstoreDatabase {
+            File(path).parentFile?.mkdirs()
+            File(path).delete()
+            val database = open(path)
+            database.writeCatalogState(
+                CatalogState(
+                    catalog = CatalogSchema.CATALOG,
+                    epoch = 0,
+                    schemaVersion = CatalogSchema.VERSION,
+                    searchModel = CatalogSchema.SEARCH_MODEL,
+                    generation = 0,
+                ),
+            )
+            return database
+        }
+
+        internal fun applySchema(connection: SQLiteConnection) {
+            connection.execSQL("PRAGMA foreign_keys = ON")
+            CatalogSchema.CREATE_STATEMENTS.forEach(connection::execSQL)
+        }
+
+        internal fun upsertCatalogState(connection: SQLiteConnection, state: CatalogState) {
+            connection.prepare(
+                """
+                INSERT INTO catalog_state(catalog, epoch, schema_version, search_model, generation)
+                VALUES (?, ?, ?, ?, ?)
+                ON CONFLICT(catalog) DO UPDATE SET
+                    epoch = excluded.epoch,
+                    schema_version = excluded.schema_version,
+                    search_model = excluded.search_model,
+                    generation = excluded.generation
+                """.trimIndent(),
+            ).use { statement ->
+                statement.bindText(1, state.catalog)
+                statement.bindLong(2, state.epoch)
+                statement.bindLong(3, state.schemaVersion.toLong())
+                statement.bindText(4, state.searchModel)
+                statement.bindLong(5, state.generation)
+                statement.step()
+            }
+        }
+
+        private fun openConnection(path: String): SQLiteConnection =
+            BundledSQLiteDriver().open(path)
+    }
+}

src/main/kotlin/dev/zapstore/app/screens/HomeScreen.kt

@@ -18,8 +18,6 @@ import androidx.compose.foundation.lazy.LazyRow
 import androidx.compose.foundation.lazy.items
 import androidx.compose.foundation.lazy.rememberLazyListState
 import androidx.compose.foundation.shape.CircleShape
-import androidx.compose.material.icons.Icons
-import androidx.compose.material.icons.filled.Notifications
 import androidx.compose.material3.Icon
 import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
@@ -45,8 +43,10 @@ fun HomeScreen(
     onSearchQueryChanged: (String) -> Unit,
     onSearchSubmitted: () -> Unit,
     onSearchCleared: () -> Unit,
-    onNotificationsClick: () -> Unit = {},
-    notificationCount: Int = 0,
+    onUpdatesClick: () -> Unit = {},
+    updateCount: Int = 0,
+    databaseRowCount: Long = 0,
+    catalogError: String? = null,
     onStackClick: (String) -> Unit,
     onAppClick: (identifier: String, author: String) -> Unit,
     onProfileClick: (String) -> Unit = {},
@@ -70,6 +70,18 @@ fun HomeScreen(
             .background(ZapCanvas)
             .windowInsetsPadding(WindowInsets.safeDrawing),
     ) {
+        Text(
+            text = buildString {
+                append(stringResource(R.string.database_rows, databaseRowCount))
+                if (!catalogError.isNullOrBlank()) {
+                    append(" · ")
+                    append(catalogError)
+                }
+            },
+            color = ZapTextTertiary,
+            style = MaterialTheme.typography.labelSmall,
+            modifier = Modifier.padding(start = 16.dp, top = 4.dp),
+        )
         Row(
             modifier = Modifier
                 .fillMaxWidth()
@@ -117,16 +129,18 @@ fun HomeScreen(
             )
             Box(contentAlignment = Alignment.TopEnd) {
                 IconButton(
-                    onClick = onNotificationsClick,
-                    modifier = Modifier.testTag("notificationsButton"),
+                    onClick = onUpdatesClick,
+                    modifier = Modifier.testTag("updatesButton"),
                 ) {
                     Icon(
-                        imageVector = Icons.Filled.Notifications,
-                        contentDescription = stringResource(R.string.notifications),
+                        painter = painterResource(R.drawable.ic_launcher),
+                        contentDescription = stringResource(R.string.updates),
+                        modifier = Modifier.size(24.dp),
                     )
                 }
+                if (updateCount > 0) {
                     Text(
-                    text = notificationCount.toString(),
+                        text = updateCount.toString(),
                         color = MaterialTheme.colorScheme.onError,
                         style = MaterialTheme.typography.labelSmall,
                         modifier = Modifier
@@ -134,10 +148,11 @@ fun HomeScreen(
                             .clip(CircleShape)
                             .background(MaterialTheme.colorScheme.error)
                             .padding(horizontal = 4.dp, vertical = 1.dp)
-                        .testTag("notificationBadge"),
+                            .testTag("updatesBadge"),
                     )
                 }
             }
+        }
 
         LazyColumn(
             modifier = Modifier.weight(1f),

src/main/kotlin/dev/zapstore/app/screens/StackDetailScreen.kt

@@ -15,7 +15,6 @@ import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.testTag
-import androidx.compose.ui.res.pluralStringResource
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.unit.dp
 
@@ -52,20 +51,10 @@ fun StackDetailScreen(
         }
 
         item {
-            Text(
-                text = stack.name,
-                style = MaterialTheme.typography.displaySmall,
-            )
-        }
-        item {
-            StatusText(
-                stack.description.ifBlank {
-                    pluralStringResource(
-                        R.plurals.curated_apps,
-                        stack.appAddresses.size,
-                        stack.appAddresses.size,
-                    )
-                },
+            StackCard(
+                stack = stack,
+                appsByAddress = state.appsByAddress,
+                modifier = Modifier.testTag("stack:${stack.event.id}"),
             )
         }
         item {
@@ -80,6 +69,7 @@ fun StackDetailScreen(
         ) { app ->
             AppCard(
                 app = app,
+                release = state.releasesByAddress[app.address],
                 onClick = { onAppClick(app.identifier, app.event.pubKey) },
                 onProfileClick = { onProfileClick(app.event.pubKey) },
                 repository = repository,

src/main/kotlin/dev/zapstore/app/screens/UpdatesScreen.kt

@@ -0,0 +1,110 @@
+package dev.zapstore.app
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.WindowInsets
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.safeDrawing
+import androidx.compose.foundation.layout.windowInsetsPadding
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.material3.FilledTonalButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.testTag
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.unit.dp
+import dev.zapstore.app.catalogsync.CatalogSyncUiState
+import java.text.DateFormat
+import java.util.Date
+
+@Composable
+fun UpdatesScreen(
+    state: CatalogSyncUiState,
+    onSync: () -> Unit,
+    onAppClick: (identifier: String, author: String?) -> Unit = { _, _ -> },
+    modifier: Modifier = Modifier,
+) {
+    Column(
+        modifier = modifier
+            .fillMaxSize()
+            .background(ZapCanvas)
+            .windowInsetsPadding(WindowInsets.safeDrawing)
+            .padding(16.dp),
+        verticalArrangement = Arrangement.spacedBy(12.dp),
+    ) {
+        Text(
+            text = stringResource(R.string.updates),
+            style = MaterialTheme.typography.displaySmall,
+        )
+        Row(
+            modifier = Modifier.fillMaxWidth(),
+            verticalAlignment = Alignment.CenterVertically,
+            horizontalArrangement = Arrangement.SpaceBetween,
+        ) {
+            Column(modifier = Modifier.weight(1f)) {
+                StatusText(stringResource(R.string.catalog_epoch, state.epoch))
+                state.lastSyncedAtMillis?.let { synced ->
+                    StatusText(
+                        stringResource(
+                            R.string.last_synced,
+                            DateFormat.getDateTimeInstance(DateFormat.MEDIUM, DateFormat.SHORT)
+                                .format(Date(synced)),
+                        ),
+                    )
+                }
+            }
+            FilledTonalButton(
+                onClick = onSync,
+                enabled = !state.syncing,
+                modifier = Modifier.testTag("syncCatalog"),
+            ) {
+                Text(stringResource(if (state.syncing) R.string.syncing else R.string.sync_now))
+            }
+        }
+        state.error?.let { StatusText(it, Modifier.testTag("updatesError")) }
+        if (state.syncing && state.availableUpdates.isEmpty()) {
+            LoadingIndicator()
+        }
+        LazyColumn(
+            modifier = Modifier.weight(1f),
+            verticalArrangement = Arrangement.spacedBy(12.dp),
+            contentPadding = PaddingValues(bottom = 24.dp),
+        ) {
+            if (state.availableUpdates.isEmpty() && !state.syncing) {
+                item {
+                    StatusText(
+                        stringResource(R.string.no_updates),
+                        Modifier.testTag("noUpdates"),
+                    )
+                }
+            }
+            items(state.availableUpdates, key = { it.appId }) { update ->
+                Column(
+                    modifier = Modifier
+                        .fillMaxWidth()
+                        .testTag("update:${update.appId}"),
+                    verticalArrangement = Arrangement.spacedBy(2.dp),
+                ) {
+                    Text(update.name, style = MaterialTheme.typography.titleMedium)
+                    EvidenceText(update.appId, color = ZapTextSecondary)
+                    StatusText(
+                        stringResource(
+                            R.string.update_version,
+                            update.installedVersion,
+                            update.availableVersion,
+                        ),
+                    )
+                }
+            }
+        }
+    }
+}

src/main/res/values/strings.xml

@@ -4,6 +4,14 @@
     <string name="clear_search">Clear search</string>
     <string name="close">Close</string>
     <string name="notifications">Notifications</string>
+    <string name="updates">Updates</string>
+    <string name="no_updates">All catalog apps are up to date.</string>
+    <string name="sync_now">Sync</string>
+    <string name="syncing">Syncing</string>
+    <string name="catalog_epoch">Catalog epoch %1$d</string>
+    <string name="last_synced">Last sync %1$s</string>
+    <string name="update_version">%1$s → %2$s</string>
+    <string name="database_rows">%1$d database rows</string>
     <string name="no_notifications">You are all caught up.</string>
     <string name="curated_stacks">Curated stacks</string>
     <string name="latest_releases">Latest releases</string>

src/main/res/xml/network_security_config.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<network-security-config>
+    <domain-config cleartextTrafficPermitted="true">
+        <domain includeSubdomains="true">10.0.2.2</domain>
+        <domain includeSubdomains="true">localhost</domain>
+        <domain includeSubdomains="true">127.0.0.1</domain>
+    </domain-config>
+</network-security-config>

src/test/kotlin/dev/zapstore/app/ViewModelsTest.kt

@@ -30,9 +30,16 @@ class ViewModelsTest {
     @Test
     fun `catalog defaults to brief one-shot freshness and profiles use one day`() {
         val options = catalogQueryOptions()
+        if (Catalog.catalogLocalOnly) {
+            assertEquals(SourceMode.Local, options.sourceMode)
+            assertEquals(null, options.remoteMode)
+            assertEquals(null, options.cachedFor)
+            assertTrue(options.relays.isEmpty())
+        } else {
             assertEquals(SourceMode.LocalAndRemote, options.sourceMode)
             assertTrue(options.remoteMode is RemoteMode.OneShot)
             assertEquals(30.seconds, options.cachedFor)
+        }
         assertEquals(1.days, PROFILE_CACHE_DURATION)
 
         val forced = catalogQueryOptions(cachedFor = null)
@@ -377,6 +384,74 @@ class ViewModelsTest {
         assertEquals("dev.example.app", release.appIdentifier)
     }
 
+    @Test
+    fun `standalone 3063 carries release notes and defaults channel to main`() {
+        val release = ReleaseInfo(
+            event(
+                kind = Catalog.assetKind,
+                tags = arrayOf(
+                    arrayOf("i", "dev.example.app"),
+                    arrayOf("version", "1.2.3"),
+                ),
+                content = "Fixed a crash",
+            ),
+        )
+
+        assertEquals("dev.example.app", release.appIdentifier)
+        assertEquals("1.2.3", release.version)
+        assertEquals("Fixed a crash", release.notes)
+        assertEquals("main", release.channel)
+    }
+
+    @Test
+    fun `30063 outranks a 3063 with the same created at`() {
+        val grouped = ReleaseInfo(
+            event(
+                id = "bb",
+                kind = Catalog.releaseKind,
+                createdAt = 100,
+                tags = arrayOf(arrayOf("i", "dev.example.app"), arrayOf("version", "1.0")),
+                content = "Grouped notes",
+            ),
+        )
+        val asset = ReleaseInfo(
+            event(
+                id = "aa",
+                kind = Catalog.assetKind,
+                createdAt = 100,
+                tags = arrayOf(arrayOf("i", "dev.example.app"), arrayOf("version", "1.0")),
+                content = "Asset notes",
+            ),
+        )
+
+        assertEquals(grouped, preferredRelease(asset, grouped))
+        assertEquals(grouped, preferredRelease(grouped, asset))
+        assertEquals(true, grouped.outranks(asset))
+    }
+
+    @Test
+    fun `30063 outranks a newer 3063 for the same version`() {
+        val grouped = ReleaseInfo(
+            event(
+                id = "rel",
+                kind = Catalog.releaseKind,
+                createdAt = 100,
+                tags = arrayOf(arrayOf("i", "dev.example.app"), arrayOf("version", "1.0")),
+            ),
+        )
+        val asset = ReleaseInfo(
+            event(
+                id = "asset",
+                kind = Catalog.assetKind,
+                createdAt = 200,
+                tags = arrayOf(arrayOf("i", "dev.example.app"), arrayOf("version", "1.0")),
+            ),
+        )
+
+        assertEquals(grouped, preferredRelease(asset, grouped))
+        assertEquals(false, asset.outranks(grouped))
+    }
+
     @Test
     fun `app detail zap receipts resolve the app author outbox`() = runTest {
         var outboxAuthors: List<String>? = null
@@ -404,6 +479,31 @@ class ViewModelsTest {
         assertEquals(Catalog.defaultZapRelays, outboxRelays)
     }
 
+    @Test
+    fun `app detail loads latest release from release and asset kinds`() = runTest {
+        val filters = mutableListOf<Filter>()
+        AppDetailViewModel(
+            FakeCatalogRepository(
+                localQuery = { filter ->
+                    filters += filter
+                    emptyFlow()
+                },
+            ),
+            SavedStateHandle(
+                mapOf(
+                    APP_IDENTIFIER_ARGUMENT to "dev.example.app",
+                    APP_AUTHOR_ARGUMENT to "a".repeat(64),
+                ),
+            ),
+        )
+        runCurrent()
+
+        val releaseFilter = filters.single { Catalog.releaseKind in it.kinds.orEmpty() }
+        assertEquals(Catalog.releaseKinds, releaseFilter.kinds)
+        assertEquals(mapOf("i" to listOf("dev.example.app")), releaseFilter.tags)
+        assertEquals(listOf("a".repeat(64)), releaseFilter.authors)
+    }
+
     @Test
     fun `app detail zap and asset queries are bounded`() = runTest {
         val filters = mutableListOf<Filter>()
@@ -515,12 +615,13 @@ private fun event(
     kind: Int,
     createdAt: Long = 1_750_000_000,
     tags: Array<Array<String>> = emptyArray(),
+    content: String = "",
 ): Event = Event(
     id = id,
     pubKey = pubKey,
     createdAt = createdAt,
     kind = kind,
     tags = tags,
-    content = "",
+    content = content,
     sig = "2".repeat(128),
 )

src/test/kotlin/dev/zapstore/app/catalogsync/CatalogSyncTest.kt

@@ -0,0 +1,48 @@
+package dev.zapstore.app.catalogsync
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class CatalogSyncTest {
+    @Test
+    fun `updates request json has only public fields`() {
+        val json = UpdatesRequest(
+            protocol = 1,
+            catalog = "default",
+            schemaVersion = 1,
+            epoch = 0,
+            searchModel = CatalogSchema.SEARCH_MODEL,
+        ).toJson()
+        assertTrue(json.contains("\"protocol\":1"))
+        assertTrue(json.contains("\"catalog\":\"default\""))
+        assertTrue(json.contains("\"schema_version\":1"))
+        assertTrue(json.contains("\"epoch\":0"))
+        assertTrue(json.contains("\"search_model\":\"${CatalogSchema.SEARCH_MODEL}\""))
+        assertTrue(!json.contains("installed"))
+        assertTrue(!json.contains("search\""))
+    }
+
+    @Test
+    fun `local matcher keeps lineage and newer version codes`() {
+        val installed = listOf(
+            InstalledApp("dev.one", 10, "1.0", setOf("aa")),
+            InstalledApp("dev.two", 20, "2.0", setOf("bb")),
+            InstalledApp("dev.three", 5, "0.5", setOf("cc")),
+        )
+        val catalog = listOf(
+            CatalogAssetRow("dev.one", "One", "1.1", 11, "stable", "android-arm64-v8a", null, "aa", LocalUpdateMatcher.ANDROID_MIME),
+            CatalogAssetRow("dev.two", "Two", "2.1", 21, "stable", "android", null, "zz", LocalUpdateMatcher.ANDROID_MIME),
+            CatalogAssetRow("dev.three", "Three", "0.4", 4, "stable", "android", null, "cc", LocalUpdateMatcher.ANDROID_MIME),
+        )
+        val updates = LocalUpdateMatcher.match(installed, catalog)
+        assertEquals(listOf("dev.one"), updates.map { it.appId })
+        assertEquals("1.1", updates.single().availableVersion)
+    }
+
+    @Test
+    fun `hex helpers round-trip`() {
+        val hex = "0a1b2c3d"
+        assertEquals(hex, hex.hexToBytes().toHex())
+    }
+}