refactor(apple): adopt Swift 6 language mode

Enable complete strict concurrency and switch the app target to Swift 6.

- Isolate model dependency protocols to @MainActor
- Make the CoreRepository blocking-FFI bridge race-free: nonisolated(unsafe)
  core handle, nonisolated runCore/readSnapshot, @Sendable work block,
  Sendable domain models
- Fix Binding method-reference captures; @preconcurrency imports for
  CoreNFC/AVFoundation/VnidropCore; isolate the NFC/QR delegate helpers

apple/VniDrop/App/AppEnvironment.swift

@@ -17,6 +17,7 @@ struct DeviceInfo {
 	let batteryLevel: String?
 }
 
+@MainActor
 protocol DeviceInfoProvider {
 	func load() async -> DeviceInfo
 }

apple/VniDrop/Core/AppPreferences.swift

@@ -2,12 +2,12 @@ import Foundation
 import Combine
 
 /// Receive-destination descriptor, ported from `core/FileSystemService.kt`.
-enum ReceiveFolderKind: String, Codable {
+enum ReceiveFolderKind: String, Codable, Sendable {
 	case fileSystemPath
 	case iosSecurityScopedUrl
 }
 
-struct ReceiveFolder: Equatable, Codable {
+struct ReceiveFolder: Equatable, Codable, Sendable {
 	let kind: ReceiveFolderKind
 	let value: String
 	let displayName: String

apple/VniDrop/Core/CoreModels.swift

@@ -4,13 +4,13 @@ import Foundation
 /// the generated UniFFI records/enums into these so the UI never depends on the
 /// binding surface directly.
 
-struct CoreStatus: Equatable {
+struct CoreStatus: Equatable, Sendable {
 	let endpointId: String
 	let activeTransfers: UInt64
 	let activeShares: UInt64
 }
 
-struct CoreEventModel: Equatable, Identifiable {
+struct CoreEventModel: Equatable, Identifiable, Sendable {
 	let id: String
 	let timestamp: Int64
 	let scope: String
@@ -21,17 +21,17 @@ struct CoreEventModel: Equatable, Identifiable {
 	let dataJson: String
 }
 
-enum ShareAccessPolicy: Equatable {
+enum ShareAccessPolicy: Equatable, Sendable {
 	case requireApproval
 	case anyoneWithTransfer
 }
 
-enum TransferDirection: Equatable {
+enum TransferDirection: Equatable, Sendable {
 	case send
 	case receive
 }
 
-enum TransferStatus: Equatable {
+enum TransferStatus: Equatable, Sendable {
 	case importing
 	case sharing
 	case receiving
@@ -41,7 +41,7 @@ enum TransferStatus: Equatable {
 	case stopped
 }
 
-struct Transfer: Equatable, Identifiable {
+struct Transfer: Equatable, Identifiable, Sendable {
 	let localId: String
 	let transferId: UInt64
 	let direction: TransferDirection
@@ -59,7 +59,7 @@ struct Transfer: Equatable, Identifiable {
 	var id: String { localId }
 }
 
-struct Share: Equatable {
+struct Share: Equatable, Sendable {
 	let transferId: UInt64
 	let ticket: String
 	let transferName: String
@@ -68,7 +68,7 @@ struct Share: Equatable {
 	let totalSize: UInt64
 }
 
-struct TransferMetadataModel: Equatable {
+struct TransferMetadataModel: Equatable, Sendable {
 	let transferId: UInt64
 	let transferName: String
 	let senderName: String?
@@ -77,12 +77,12 @@ struct TransferMetadataModel: Equatable {
 	let totalSize: UInt64
 }
 
-struct TicketInspectionModel: Equatable {
+struct TicketInspectionModel: Equatable, Sendable {
 	let kind: String
 	let metadata: TransferMetadataModel
 }
 
-enum ReceiverDeliveryStatus: Equatable {
+enum ReceiverDeliveryStatus: Equatable, Sendable {
 	case requested
 	case accepted
 	case refused
@@ -91,7 +91,7 @@ enum ReceiverDeliveryStatus: Equatable {
 	case unknown
 }
 
-struct ReceiverRequestModel: Equatable, Identifiable {
+struct ReceiverRequestModel: Equatable, Identifiable, Sendable {
 	let id: String
 	let transferId: UInt64
 	let remoteEndpointId: String
@@ -106,7 +106,7 @@ struct ReceiverRequestModel: Equatable, Identifiable {
 	let completedAt: Int64?
 }
 
-struct CoreState: Equatable {
+struct CoreState: Equatable, Sendable {
 	var isInitialized: Bool = false
 	var status: CoreStatus?
 	var events: [CoreEventModel] = []
@@ -116,7 +116,7 @@ struct CoreState: Equatable {
 }
 
 /// Coalesced change hints emitted from the event sink, ported from `CoreSignal`.
-enum CoreSignal: Equatable {
+enum CoreSignal: Equatable, Sendable {
 	case approvalChanged(transferId: UInt64)
 	case receiverHistoryChanged(transferId: UInt64)
 	/// Transfer status/history changed enough to re-read the durable snapshot.

apple/VniDrop/Core/CoreRepository.swift

@@ -1,6 +1,6 @@
 import Foundation
 import Combine
-import VnidropCore
+@preconcurrency import VnidropCore
 
 /// Swift port of `core/CoreRepository.kt`. Owns the `VnidropCore` handle, maps the
 /// generated UniFFI records into app domain models, publishes an observable
@@ -16,13 +16,16 @@ final class CoreRepository: ObservableObject {
 	/// Coalesced change hints; subscribe to react to approval/history/transfer changes.
 	var signals: AnyPublisher<CoreSignal, Never> { signalsSubject.eraseToAnyPublisher() }
 
-	private var core: VnidropCore?
+	// Set on the main actor (initialize/shutdown) but read from `queue` inside
+	// `runCore`; the underlying core is internally synchronized, so this crossing
+	// is safe. `nonisolated(unsafe)` documents that contract for Swift 6.
+	private nonisolated(unsafe) var core: VnidropCore?
 	private let queue = DispatchQueue(label: "com.vnidrop.core", qos: .userInitiated)
 	private lazy var sink = RepositoryEventSink { [weak self] event in
 		Task { @MainActor in self?.handle(event: event) }
 	}
 
-	private static let maxEvents = 200
+	private nonisolated static let maxEvents = 200
 
 	// MARK: - Lifecycle
 
@@ -186,7 +189,7 @@ final class CoreRepository: ObservableObject {
 	// MARK: - Internals
 
 	/// Snapshot of the values read from the core in one pass.
-	private struct CoreSnapshot {
+	private struct CoreSnapshot: Sendable {
 		let status: CoreStatus
 		let transfers: [Transfer]
 		let events: [CoreEventModel]
@@ -194,11 +197,11 @@ final class CoreRepository: ObservableObject {
 
 	/// Reads the current core state. Safe to call off the main actor (pure core
 	/// FFI reads); does not touch `@Published` state.
-	private func readSnapshot() -> CoreSnapshot? {
+	private nonisolated func readSnapshot() -> CoreSnapshot? {
 		guard let core = self.core else { return nil }
 		let status = core.status()
-		let transfers = (try? core.listTransfers())?.map { $0.toModel() } ?? state.transfers
-		let events = (try? core.listEvents(transferId: nil))?.prefix(Self.maxEvents).map { $0.toModel() } ?? state.events
+		let transfers = (try? core.listTransfers())?.map { $0.toModel() } ?? []
+		let events = (try? core.listEvents(transferId: nil))?.prefix(Self.maxEvents).map { $0.toModel() } ?? []
 		return CoreSnapshot(
 			status: CoreStatus(
 				endpointId: status.endpointId,
@@ -221,7 +224,7 @@ final class CoreRepository: ObservableObject {
 		if let snapshot = readSnapshot() { applySnapshot(snapshot) }
 	}
 
-	private func requireCore() throws -> VnidropCore {
+	private nonisolated func requireCore() throws -> VnidropCore {
 		guard let core = self.core else {
 			throw InvitationError.message("Initialize the core first.")
 		}
@@ -229,7 +232,7 @@ final class CoreRepository: ObservableObject {
 	}
 
 	/// Runs a blocking core call off the main actor and hops the result back.
-	private func runCore<T>(_ block: @escaping () throws -> T) async -> Result<T, Error> {
+	private nonisolated func runCore<T: Sendable>(_ block: @escaping @Sendable () throws -> T) async -> Result<T, Error> {
 		await withCheckedContinuation { continuation in
 			queue.async {
 				let result: Result<T, Error>
@@ -243,7 +246,7 @@ final class CoreRepository: ObservableObject {
 		}
 	}
 
-	private static func nextTransferId() -> UInt64 {
+	private nonisolated static func nextTransferId() -> UInt64 {
 		UInt64.random(in: 1...UInt64(Int64.max))
 	}
 }

apple/VniDrop/Core/FileSystemService.swift

@@ -3,7 +3,7 @@ import VnidropCore
 
 /// A file/folder selected for sharing, ported from `PickedShareFile` in
 /// `core/FilePicker.kt`.
-struct PickedShareFile: Equatable, Identifiable {
+struct PickedShareFile: Equatable, Identifiable, Sendable {
 	let value: String
 	let displayName: String
 	var sizeBytes: UInt64? = nil
@@ -18,6 +18,7 @@ struct PickedShareFile: Equatable, Identifiable {
 
 /// Receive-destination and share-source platform bridge, ported from
 /// `core/FileSystemService.kt` and its iOS/desktop actuals.
+@MainActor
 protocol FileSystemService {
 	var supportsCustomReceiveFolders: Bool { get }
 

apple/VniDrop/Features/Receive/ReceiveInvitationActions.swift

@@ -118,7 +118,7 @@ struct InvitationReviewPanel: View {
 				.background(colors.backgroundSurface200, in: RoundedRectangle(cornerRadius: 14))
 
 				Field(label: String(localized: "field_receiver_name"),
-					  value: Binding(get: { state.receiverName }, set: model.setReceiverName))
+					  value: Binding(get: { state.receiverName }, set: { model.setReceiverName($0) }))
 				Text(state.receiveFolder?.displayName ?? String(localized: "value_unavailable"))
 					.font(VniType.bodySmall)
 					.foregroundStyle(state.folderAccessStatus == .writable ? colors.foregroundLight : colors.destructiveDefault)

apple/VniDrop/Features/Send/TransferComposer.swift

@@ -52,9 +52,9 @@ struct TransferComposer: View {
 				)
 			}
 			Field(label: String(localized: "field_transfer_name"),
-				  value: Binding(get: { state.transferName }, set: model.setTransferName))
+				  value: Binding(get: { state.transferName }, set: { model.setTransferName($0) }))
 			Field(label: String(localized: "field_sender_name"),
-				  value: Binding(get: { state.senderName }, set: model.setSenderName))
+				  value: Binding(get: { state.senderName }, set: { model.setSenderName($0) }))
 			Text(LocalizedStringKey("send_access_title")).font(.headline)
 			PolicyOption(
 				icon: "checkmark.shield", titleKey: "send_access_approval", descKey: "send_access_approval_description",

apple/VniDrop/Features/Settings/BugReportService.swift

@@ -11,6 +11,7 @@ struct BugReportDraft {
 
 /// Bug-report submission. The full diagnostics transport (URLSession + build
 /// config) lands in the diagnostics phase; this protocol is the stable seam.
+@MainActor
 protocol BugReportService {
 	func submit(_ draft: BugReportDraft, deviceInfo: DeviceInfo?) async -> Result<Void, Error>
 	func previewLogBytes() async -> Int

apple/VniDrop/Features/Settings/SettingsSections.swift

@@ -9,7 +9,7 @@ struct PreferencesSettings: View {
 	var body: some View {
 		Section(String(localized: "field_username")) {
 			TextField(String(localized: "field_username"),
-					  text: Binding(get: { model.state.username }, set: model.setUsername))
+					  text: Binding(get: { model.state.username }, set: { model.setUsername($0) }))
 		}
 		if model.state.supportsCustomReceiveFolders {
 			Section(String(localized: "preferences_receive_folder_title")) {
@@ -228,25 +228,25 @@ struct BugReportSettings: View {
 
 	var body: some View {
 		Section(String(localized: "bug_report_what_label")) {
-			TextField("", text: Binding(get: { model.state.bugWhatHappened }, set: model.setBugWhatHappened),
+			TextField("", text: Binding(get: { model.state.bugWhatHappened }, set: { model.setBugWhatHappened($0) }),
 					  prompt: Text(LocalizedStringKey("bug_report_what_hint")), axis: .vertical)
 				.lineLimit(3, reservesSpace: true)
 				.labelsHidden()
 		}
 		Section(String(localized: "bug_report_expected_label")) {
-			TextField("", text: Binding(get: { model.state.bugExpected }, set: model.setBugExpected),
+			TextField("", text: Binding(get: { model.state.bugExpected }, set: { model.setBugExpected($0) }),
 					  prompt: Text(LocalizedStringKey("bug_report_expected_hint")), axis: .vertical)
 				.lineLimit(3, reservesSpace: true)
 				.labelsHidden()
 		}
 		Section(String(localized: "bug_report_steps_label")) {
-			TextField("", text: Binding(get: { model.state.bugSteps }, set: model.setBugSteps),
+			TextField("", text: Binding(get: { model.state.bugSteps }, set: { model.setBugSteps($0) }),
 					  prompt: Text(LocalizedStringKey("bug_report_steps_hint")), axis: .vertical)
 				.lineLimit(3, reservesSpace: true)
 				.labelsHidden()
 		}
 		Section(String(localized: "bug_report_contact_label")) {
-			TextField("", text: Binding(get: { model.state.bugContact }, set: model.setBugContact),
+			TextField("", text: Binding(get: { model.state.bugContact }, set: { model.setBugContact($0) }),
 					  prompt: Text(LocalizedStringKey("bug_report_contact_hint")))
 				.labelsHidden()
 		}

apple/VniDrop/Platform/ReceiveInvitationActions+iOS.swift

@@ -1,7 +1,7 @@
 #if os(iOS)
 import UIKit
-import AVFoundation
-import CoreNFC
+@preconcurrency import AVFoundation
+@preconcurrency import CoreNFC
 import UniformTypeIdentifiers
 
 @MainActor
@@ -98,6 +98,8 @@ final class IosReceiveInvitationActions: NSObject, ReceiveInvitationActions, UID
 		case .authorized:
 			completion(true)
 		case .notDetermined:
+			// The permission callback is delivered back on the main queue.
+			nonisolated(unsafe) let completion = completion
 			AVCaptureDevice.requestAccess(for: .video) { granted in
 				DispatchQueue.main.async { completion(granted) }
 			}
@@ -183,11 +185,14 @@ final class QrScannerViewController: UIViewController, AVCaptureMetadataOutputOb
 		DispatchQueue.global(qos: .userInitiated).async { [session] in session.startRunning() }
 	}
 
-	func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
+	// The metadata output delegate queue is `.main`, so hop back onto the main
+	// actor to touch view-controller state.
+	nonisolated func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
 		let value = metadataObjects
 			.compactMap { $0 as? AVMetadataMachineReadableCodeObject }
 			.first { $0.type == .qr }?.stringValue?.trimmingCharacters(in: .whitespacesAndNewlines) ?? ""
-		if !value.isEmpty { finish(.success(value)) }
+		guard !value.isEmpty else { return }
+		MainActor.assumeIsolated { finish(.success(value)) }
 	}
 
 	private func finish(_ result: Result<String, Error>) {
@@ -203,7 +208,8 @@ final class QrScannerViewController: UIViewController, AVCaptureMetadataOutputOb
 }
 
 /// NFC invitation reader, ported from `InvitationNfcReader`.
-final class InvitationNfcReader: NSObject, NFCNDEFReaderSessionDelegate {
+// Runs entirely on the NFC session's `.main` delegate queue.
+final class InvitationNfcReader: NSObject, NFCNDEFReaderSessionDelegate, @unchecked Sendable {
 	private let onResult: (Result<String, Error>) -> Void
 	private var session: NFCNDEFReaderSession?
 	private var finished = false

apple/VniDrop/Platform/TransferShareActions+iOS.swift

@@ -1,6 +1,6 @@
 #if os(iOS)
 import UIKit
-import CoreNFC
+@preconcurrency import CoreNFC
 
 @MainActor
 func makePlatformShareActions() -> TransferShareActions { IosTransferShareActions() }
@@ -63,7 +63,8 @@ final class IosTransferShareActions: NSObject, TransferShareActions {
 
 /// Writes a VniDrop invitation to a writable NDEF tag, ported from
 /// `InvitationNfcWriter` in `TransferShareActions.ios.kt`.
-final class InvitationNfcWriter: NSObject, NFCNDEFReaderSessionDelegate {
+// Runs entirely on the NFC session's `.main` delegate queue.
+final class InvitationNfcWriter: NSObject, NFCNDEFReaderSessionDelegate, @unchecked Sendable {
 	private let ticket: String
 	private let onResult: (Result<Void, Error>) -> Void
 	private var session: NFCNDEFReaderSession?
@@ -95,9 +96,13 @@ final class InvitationNfcWriter: NSObject, NFCNDEFReaderSessionDelegate {
 	func readerSession(_ session: NFCNDEFReaderSession, didDetectNDEFs messages: [NFCNDEFMessage]) {}
 
 	func readerSession(_ session: NFCNDEFReaderSession, didDetect tags: [NFCNDEFTag]) {
-		guard let tag = tags.first else {
+		guard let firstTag = tags.first else {
 			return finish(.failure(InvitationError.message("No NFC tag was detected")))
 		}
+		// CoreNFC completion handlers run on the session's `.main` queue; these
+		// framework values are safe to use there.
+		nonisolated(unsafe) let session = session
+		nonisolated(unsafe) let tag = firstTag
 		session.connect(to: tag) { [weak self] connectError in
 			guard let self else { return }
 			if let connectError { return self.finish(.failure(connectError)) }

apple/project.yml

@@ -37,7 +37,8 @@ targets:
         # (the editor reads these build settings, not the manual plist).
         INFOPLIST_KEY_CFBundleDisplayName: VniDrop
         INFOPLIST_KEY_LSApplicationCategoryType: public.app-category.utilities
-        SWIFT_VERSION: "5.9"
+        SWIFT_VERSION: "6.0"
+        SWIFT_STRICT_CONCURRENCY: complete
         ENABLE_USER_SCRIPT_SANDBOXING: NO
         ASSETCATALOG_COMPILER_APPICON_NAME: AppIcon
         CODE_SIGN_STYLE: Automatic