feat(shared): enable experimental saved-devices on desktop

Surface Settings → Experimental on Windows/Linux Compose, keep generic
Desktop hosts gated off, and assert path-based targeted receive when no
output sink is available.

Co-authored-by: Cursor <cursoragent@cursor.com>

shared/docs/saved-devices-ui-contract.md

@@ -10,8 +10,8 @@ Use **saved device**, **device relationship**, **targeted transfer**, **invitati
 
 ## Experimental gate
 
-- KMP Android: Settings → Experimental → Saved devices, preference default **off**, persisted.
+- KMP Android / Windows / Linux: Settings → Experimental → Saved devices, preference default **off**, persisted.
-- KMP desktop: experimental UI **hidden**.
+- KMP generic desktop host (`UiPlatform.Desktop`, e.g. macOS JVM): experimental UI **hidden**.
 - Apple: gate shape is platform-owned; semantics below still apply when the feature is enabled.
 
 ## Events are wake-ups
@@ -35,7 +35,9 @@ After a completed invitation transfer, eligibility may exist. The user may accep
    - `Declined`
    - `AlreadySettled { transfer_id }`
 3. Never accept or display authorization/grant strings across the public binding.
-4. Pull / resume with **transfer id + destination** (path or output sink). Android KMP reuses the invitation MediaStore Downloads sink for the experimental MVP receive.
+4. Pull / resume with **transfer id + destination** (path or output sink).
+   - Android KMP: invitation MediaStore Downloads sink for the experimental MVP receive.
+   - Windows / Linux KMP: configured filesystem receive folder path when no output sink is provided.
 
 ## Out of this contract’s MVP chrome
 

shared/src/commonMain/kotlin/com/vnidrop/app/Platform.kt

@@ -14,6 +14,14 @@ enum class UiPlatform {
 val UiPlatform.isDesktop: Boolean
 	get() = this != UiPlatform.Android
 
+/** Experimental saved-devices Settings chrome for Android + Windows/Linux Compose. */
+fun showsExperimentalSavedDevices(uiPlatform: UiPlatform): Boolean = when (uiPlatform) {
+	UiPlatform.Android,
+	UiPlatform.Windows,
+	UiPlatform.Linux -> true
+	UiPlatform.Desktop -> false
+}
+
 data class PlatformEnvironment(
 	val name: String,
 	val appVersion: String,

shared/src/commonMain/kotlin/com/vnidrop/app/feature/saveddevices/TargetedOfferCoordinator.kt

@@ -32,7 +32,8 @@ data class TargetedOfferState(
 
 /**
  * Foreground interrupt for pending targeted offers. Approve pulls by transfer id
- * through the configured receive sink (MediaStore Downloads on Android).
+ * through the platform receive destination (MediaStore Downloads sink on Android,
+ * filesystem path on desktop when no sink is available).
  */
 class TargetedOfferCoordinator(
 	private val repository: CoreGateway,

shared/src/commonMain/kotlin/com/vnidrop/app/feature/settings/SettingsRoute.kt

@@ -4,7 +4,7 @@ import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
-import com.vnidrop.app.UiPlatform
+import com.vnidrop.app.showsExperimentalSavedDevices
 import com.vnidrop.app.core.rememberReceiveFolderPicker
 import com.vnidrop.app.core.rememberShareFilePicker
 import com.vnidrop.app.feature.saveddevices.SavedDevicesEffect
@@ -20,7 +20,7 @@ fun SettingsRoute(
 ) {
 	val state by viewModel.state.collectAsStateWithLifecycle()
 	val savedDevicesState by savedDevicesViewModel.state.collectAsStateWithLifecycle()
-	val showExperimental = LocalUiPlatform.current == UiPlatform.Android
+	val showExperimental = showsExperimentalSavedDevices(LocalUiPlatform.current)
 	val folderPicker = rememberReceiveFolderPicker(viewModel::onReceiveFolderPicked, viewModel::onReceiveFolderPickFailed)
 	val sharePicker = rememberShareFilePicker(
 		savedDevicesViewModel::onFilesPicked,

shared/src/commonTest/kotlin/com/vnidrop/app/ExperimentalSavedDevicesGateTest.kt

@@ -0,0 +1,15 @@
+package com.vnidrop.app
+
+import kotlin.test.Test
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+class ExperimentalSavedDevicesGateTest {
+	@Test
+	fun experimentalChromeIsShownOnAndroidWindowsAndLinuxOnly() {
+		assertTrue(showsExperimentalSavedDevices(UiPlatform.Android))
+		assertTrue(showsExperimentalSavedDevices(UiPlatform.Windows))
+		assertTrue(showsExperimentalSavedDevices(UiPlatform.Linux))
+		assertFalse(showsExperimentalSavedDevices(UiPlatform.Desktop))
+	}
+}

shared/src/commonTest/kotlin/com/vnidrop/app/feature/saveddevices/TargetedOfferCoordinatorTest.kt

@@ -14,6 +14,7 @@ import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.test.advanceUntilIdle
 import kotlinx.coroutines.test.runCurrent
 import kotlinx.coroutines.test.runTest
+import uniffi.vnidrop.ReceiveOutputSinkV2
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertTrue
@@ -43,6 +44,40 @@ class TargetedOfferCoordinatorTest {
 		advanceUntilIdle()
 		assertEquals(listOf("transfer-1" to true), core.respondedTargetedOffers)
 		assertEquals(listOf("transfer-1"), core.receivedTargetedTransferIds)
+		assertEquals(listOf("transfer-1" to "/tmp"), core.receivedTargetedPathDirs)
+		assertTrue(core.receivedTargetedViaSinkIds.isEmpty())
+	}
+
+	@Test
+	fun acceptUsesOutputSinkWhenPlatformProvidesOne() = runTest {
+		val sink = object : ReceiveOutputSinkV2 {
+			override fun startFile(relativePath: String) = error("unused")
+			override fun writeChunk(relativePath: String, bytes: ByteArray) = error("unused")
+			override fun finishFile(relativePath: String) = error("unused")
+			override fun abortFile(relativePath: String, reason: String) = error("unused")
+		}
+		val core = FakeCoreGateway().apply {
+			pendingTargetedOffers = listOf(offer("transfer-sink"))
+			respondTargetedResult = Result.success(TargetedOfferResponseModel.Approved("transfer-sink"))
+			receiveResult = Result.success(Unit)
+		}
+		val coordinator = TargetedOfferCoordinator(
+			core,
+			FakeFileSystemService(
+				ReceiveFolder(ReceiveFolderKind.AndroidPublicDownloads, "downloads", "Downloads"),
+				receiveOutputSink = sink,
+			),
+			preferences(enabled = true),
+			UiMessageController(),
+			backgroundScope,
+		)
+		runCurrent()
+		advanceUntilIdle()
+		coordinator.accept("transfer-sink")
+		runCurrent()
+		advanceUntilIdle()
+		assertEquals(listOf("transfer-sink"), core.receivedTargetedViaSinkIds)
+		assertTrue(core.receivedTargetedPathDirs.isEmpty())
 	}
 
 	@Test

shared/src/commonTest/kotlin/com/vnidrop/app/support/Fakes.kt

@@ -228,6 +228,8 @@ class FakeCoreGateway : CoreGateway {
 	var respondPairingResult: Result<Boolean> = Result.success(true)
 	val createdTargetedTransfers = mutableListOf<Triple<String, List<uniffi.vnidrop.ShareSource>, String?>>()
 	val receivedTargetedTransferIds = mutableListOf<String>()
+	val receivedTargetedPathDirs = mutableListOf<Pair<String, String>>()
+	val receivedTargetedViaSinkIds = mutableListOf<String>()
 	val respondedTargetedOffers = mutableListOf<Pair<String, Boolean>>()
 
 	override suspend fun requestSavedDevicePairing(peerEndpointId: String): Result<Boolean> {
@@ -280,6 +282,7 @@ class FakeCoreGateway : CoreGateway {
 	override suspend fun listTargetedTransfers() = Result.success(targetedTransfers)
 	override suspend fun receiveTargetedTransfer(transferId: String, outputDir: String): Result<Unit> {
 		receivedTargetedTransferIds += transferId
+		receivedTargetedPathDirs += transferId to outputDir
 		return receiveResult
 	}
 	override suspend fun receiveTargetedTransferWithOutputSink(
@@ -287,6 +290,7 @@ class FakeCoreGateway : CoreGateway {
 		outputSink: ReceiveOutputSink,
 	): Result<Unit> {
 		receivedTargetedTransferIds += transferId
+		receivedTargetedViaSinkIds += transferId
 		return receiveResult
 	}
 	override suspend fun receiveTargetedTransferWithOutputSinkV2(
@@ -294,6 +298,7 @@ class FakeCoreGateway : CoreGateway {
 		outputSink: ReceiveOutputSinkV2,
 	): Result<Unit> {
 		receivedTargetedTransferIds += transferId
+		receivedTargetedViaSinkIds += transferId
 		return receiveResult
 	}
 	override suspend fun resumeTargetedTransfer(id: String, outputDir: String) = receiveResult
@@ -348,6 +353,7 @@ class FakeNotificationService(
 
 class FakeFileSystemService(
 	private val folder: ReceiveFolder,
+	private val receiveOutputSink: ReceiveOutputSinkV2? = null,
 ) : FileSystemService {
 	var supportsCustomFolders = true
 	var effectiveFolder: ReceiveFolder? = null
@@ -369,7 +375,7 @@ class FakeFileSystemService(
 		reclaimTemporaryStorageCount += 1
 		return reclaimedTemporaryBytes
 	}
-	override fun createReceiveOutputSink(folder: ReceiveFolder): ReceiveOutputSinkV2? = null
+	override fun createReceiveOutputSink(folder: ReceiveFolder): ReceiveOutputSinkV2? = receiveOutputSink
 	override fun canRevealReceiveFolder(folder: ReceiveFolder) = canRevealFolder
 	override suspend fun revealReceiveFolder(folder: ReceiveFolder): Result<Unit> {
 		revealedFolders += folder

shared/src/jvmTest/kotlin/com/vnidrop/app/ui/FoundationComposeTest.kt

@@ -84,6 +84,7 @@ import vnidrop.shared.generated.resources.button_create_new_transfer
 import vnidrop.shared.generated.resources.button_download_invitation
 import vnidrop.shared.generated.resources.button_open_settings
 import vnidrop.shared.generated.resources.button_receive_files
+import vnidrop.shared.generated.resources.experimental_settings_title
 import vnidrop.shared.generated.resources.nav_receive
 import vnidrop.shared.generated.resources.nav_send
 import vnidrop.shared.generated.resources.notifications_description
@@ -397,6 +398,60 @@ class FoundationComposeTest {
 		runOnIdle { assertTrue(opened) }
 	}
 
+	@Test
+	fun desktopSettingsShowsExperimentalWhenGateEnabled() = runComposeUiTest {
+		setContent {
+			VniDropTheme(isDarkTheme = false) {
+				SettingsScreen(
+					state = SettingsState(),
+					windowClass = WindowClass.Desktop,
+					showExperimental = true,
+					onSectionSelected = {},
+					onUsernameChanged = {},
+					onThemeModeChanged = {},
+					onChooseFolder = {},
+					onResetFolder = {},
+					onNotificationsChanged = {},
+					onOpenNotificationSettings = {},
+					onBugWhatChanged = {},
+					onBugExpectedChanged = {},
+					onBugStepsChanged = {},
+					onBugContactChanged = {},
+					onBugIncludeLogsChanged = {},
+					onSubmitBugReport = {},
+				)
+			}
+		}
+		onNodeWithText(Res.string.experimental_settings_title.value).assertIsDisplayed()
+	}
+
+	@Test
+	fun unsupportedDesktopHostHidesExperimentalSection() = runComposeUiTest {
+		setContent {
+			VniDropTheme(isDarkTheme = false) {
+				SettingsScreen(
+					state = SettingsState(),
+					windowClass = WindowClass.Desktop,
+					showExperimental = false,
+					onSectionSelected = {},
+					onUsernameChanged = {},
+					onThemeModeChanged = {},
+					onChooseFolder = {},
+					onResetFolder = {},
+					onNotificationsChanged = {},
+					onOpenNotificationSettings = {},
+					onBugWhatChanged = {},
+					onBugExpectedChanged = {},
+					onBugStepsChanged = {},
+					onBugContactChanged = {},
+					onBugIncludeLogsChanged = {},
+					onSubmitBugReport = {},
+				)
+			}
+		}
+		onAllNodesWithText(Res.string.experimental_settings_title.value).assertCountEquals(0)
+	}
+
 	@Test
 	fun snackbarDisplaysBufferedMessage() = runComposeUiTest {
 		val controller = UiMessageController()