feat(send): share folders as multi-file collections

Add folder pickers on Android, iOS, and desktop. Desktop and iOS walk
directory paths in Rust; Android expands SAF trees to per-file FDs
with relative collection paths because directory FDs are unsupported.

shared/src/commonMain/kotlin/com/vnidrop/app/core/FilePicker.kt

@@ -7,11 +7,20 @@ data class PickedShareFile(
 	val displayName: String,
 	val sizeBytes: ULong? = null,
 	val thumbnailBytes: ByteArray? = null,
+	/**
+	 * When true, [value] is a directory (filesystem path, iOS security-scoped
+	 * folder URL, or Android document tree URI). Platform share code expands or
+	 * walks it; Rust cannot treat an Android FD as a directory.
+	 */
+	val isDirectory: Boolean = false,
 )
 
 interface ShareFilePicker {
 	/** Opens a platform picker that may return one or more files. */
 	fun pickFiles()
+
+	/** Opens a platform folder picker for sharing a directory as one transfer. */
+	fun pickFolder()
 }
 
 interface ReceiveFolderPicker {

shared/src/commonMain/kotlin/com/vnidrop/app/feature/send/SendRoute.kt

@@ -24,6 +24,7 @@ fun SendRoute(
 		viewModel.effectFlow.collect { effect ->
 			when (effect) {
 				SendEffect.OpenFilePicker -> picker.pickFiles()
+				SendEffect.OpenFolderPicker -> picker.pickFolder()
 				is SendEffect.CopyTicket -> clipboard.setText(AnnotatedString(effect.ticket))
 			}
 		}
@@ -37,6 +38,7 @@ fun SendRoute(
 		onOpenComposer = viewModel::openComposer,
 		onDismissComposer = viewModel::dismissComposer,
 		onSelectFile = viewModel::selectFile,
+		onSelectFolder = viewModel::selectFolder,
 		onClearFile = viewModel::clearSelectedSource,
 		onRemoveFile = viewModel::removeSelectedFile,
 		onTransferNameChanged = viewModel::setTransferName,

shared/src/commonMain/kotlin/com/vnidrop/app/feature/send/SendScreen.kt

@@ -24,6 +24,7 @@ fun SendScreen(
 	onOpenComposer: () -> Unit,
 	onDismissComposer: () -> Unit,
 	onSelectFile: () -> Unit,
+	onSelectFolder: () -> Unit = {},
 	onClearFile: () -> Unit,
 	onRemoveFile: (String) -> Unit = {},
 	onTransferNameChanged: (String) -> Unit,
@@ -83,6 +84,7 @@ fun SendScreen(
 				state = state,
 				windowClass = windowClass,
 				onSelectFile = onSelectFile,
+				onSelectFolder = onSelectFolder,
 				onClearFile = onClearFile,
 				onRemoveFile = onRemoveFile,
 				onTransferNameChanged = onTransferNameChanged,

shared/src/commonMain/kotlin/com/vnidrop/app/feature/send/SendViewModel.kt

@@ -54,6 +54,7 @@ enum class TransferDetailPanel { Activity, Receivers, Share }
 
 sealed interface SendEffect {
 	data object OpenFilePicker : SendEffect
+	data object OpenFolderPicker : SendEffect
 	data class CopyTicket(val ticket: String) : SendEffect
 }
 
@@ -135,6 +136,7 @@ class SendViewModel(
 	}
 
 	fun selectFile() = sendEffect(SendEffect.OpenFilePicker)
+	fun selectFolder() = sendEffect(SendEffect.OpenFolderPicker)
 
 	fun onFilesPicked(files: List<PickedShareFile>) {
 		if (files.isEmpty()) return
@@ -271,9 +273,11 @@ class SendViewModel(
 		}
 	}
 
-	private fun defaultTransferName(files: List<PickedShareFile>): String = when (files.size) {
-		0 -> ""
-		1 -> files.first().displayName
+	private fun defaultTransferName(files: List<PickedShareFile>): String = when {
+		files.isEmpty() -> ""
+		files.size == 1 && files.first().isDirectory -> files.first().displayName
+		files.size == 1 -> files.first().displayName
+		files.all { it.isDirectory } -> "${files.size} folders"
 		else -> "${files.size} files"
 	}
 

shared/src/commonMain/kotlin/com/vnidrop/app/feature/send/TransferComposer.kt

@@ -42,6 +42,7 @@ import org.jetbrains.compose.resources.stringResource
 import vnidrop.shared.generated.resources.Res
 import vnidrop.shared.generated.resources.button_change_files
 import vnidrop.shared.generated.resources.button_choose_files
+import vnidrop.shared.generated.resources.button_choose_folder
 import vnidrop.shared.generated.resources.button_clear
 import vnidrop.shared.generated.resources.button_remove_file
 import vnidrop.shared.generated.resources.button_share_file
@@ -56,6 +57,7 @@ import vnidrop.shared.generated.resources.send_access_title
 import vnidrop.shared.generated.resources.send_choose_file_body
 import vnidrop.shared.generated.resources.send_choose_file_title
 import vnidrop.shared.generated.resources.send_file_size_unknown
+import vnidrop.shared.generated.resources.send_folder_label
 import vnidrop.shared.generated.resources.send_review_title
 import vnidrop.shared.generated.resources.send_selected_files_count
 
@@ -65,6 +67,7 @@ internal fun TransferComposer(
 	state: SendState,
 	windowClass: WindowClass,
 	onSelectFile: () -> Unit,
+	onSelectFolder: () -> Unit,
 	onClearFile: () -> Unit,
 	onRemoveFile: (String) -> Unit,
 	onTransferNameChanged: (String) -> Unit,
@@ -77,12 +80,13 @@ internal fun TransferComposer(
 		verticalArrangement = Arrangement.spacedBy(16.dp),
 	) {
 		if (state.selectedFiles.isEmpty()) {
-			ChooseFileStep(onSelectFile)
+			ChooseFileStep(onSelectFile, onSelectFolder)
 		} else {
 			ReviewFileStep(
 				state = state,
 				windowClass = windowClass,
 				onSelectFile = onSelectFile,
+				onSelectFolder = onSelectFolder,
 				onClearFile = onClearFile,
 				onRemoveFile = onRemoveFile,
 				onTransferNameChanged = onTransferNameChanged,
@@ -96,7 +100,7 @@ internal fun TransferComposer(
 }
 
 @Composable
-private fun ChooseFileStep(onSelectFile: () -> Unit) {
+private fun ChooseFileStep(onSelectFile: () -> Unit, onSelectFolder: () -> Unit) {
 	Text(stringResource(Res.string.send_choose_file_title), style = MaterialTheme.typography.titleLarge, fontWeight = FontWeight.SemiBold)
 	Text(
 		stringResource(Res.string.send_choose_file_body),
@@ -111,6 +115,7 @@ private fun ChooseFileStep(onSelectFile: () -> Unit) {
 		) {
 			Icon(SendIcons.File, contentDescription = null, tint = LocalVniDropColors.current.brandLink, modifier = Modifier.size(32.dp))
 			PrimaryButton(stringResource(Res.string.button_choose_files), onClick = onSelectFile)
+			QuietButton(stringResource(Res.string.button_choose_folder), onClick = onSelectFolder)
 		}
 	}
 }
@@ -120,6 +125,7 @@ private fun ReviewFileStep(
 	state: SendState,
 	windowClass: WindowClass,
 	onSelectFile: () -> Unit,
+	onSelectFolder: () -> Unit,
 	onClearFile: () -> Unit,
 	onRemoveFile: (String) -> Unit,
 	onTransferNameChanged: (String) -> Unit,
@@ -164,11 +170,13 @@ private fun ReviewFileStep(
 		Column(verticalArrangement = Arrangement.spacedBy(8.dp)) {
 			ShareButton(state, coreInitialized, onCreateShare, Modifier.fillMaxWidth())
 			QuietButton(stringResource(Res.string.button_change_files), onClick = onSelectFile, modifier = Modifier.fillMaxWidth(), enabled = !state.isSharing)
+			QuietButton(stringResource(Res.string.button_choose_folder), onClick = onSelectFolder, modifier = Modifier.fillMaxWidth(), enabled = !state.isSharing)
 		}
 	} else {
 		Row(horizontalArrangement = Arrangement.spacedBy(8.dp)) {
 			ShareButton(state, coreInitialized, onCreateShare)
 			QuietButton(stringResource(Res.string.button_change_files), onClick = onSelectFile, enabled = !state.isSharing)
+			QuietButton(stringResource(Res.string.button_choose_folder), onClick = onSelectFolder, enabled = !state.isSharing)
 			QuietButton(stringResource(Res.string.button_clear), onClick = onClearFile, enabled = !state.isSharing)
 		}
 	}
@@ -199,7 +207,11 @@ private fun SelectedFileCard(
 			Column(Modifier.weight(1f), verticalArrangement = Arrangement.spacedBy(3.dp)) {
 				Text(file.displayName, fontWeight = FontWeight.SemiBold, maxLines = 1, overflow = TextOverflow.Ellipsis)
 				Text(
-					file.sizeBytes?.let(::formatBytes) ?: stringResource(Res.string.send_file_size_unknown),
+					when {
+						file.isDirectory -> stringResource(Res.string.send_folder_label)
+						file.sizeBytes != null -> formatBytes(file.sizeBytes)
+						else -> stringResource(Res.string.send_file_size_unknown)
+					},
 					color = LocalVniDropColors.current.foregroundLighter,
 					style = MaterialTheme.typography.bodySmall,
 				)