iOS: native upload and download services (background URLSession)

Swift implementation of the upload_service/download_service channels:
background PUT/GET against the account's WebDAV root, one summary local
notification per batch, Downloads visible in the Files app. Pure helpers
covered by RunnerTests.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

ios/Runner/Native/NativeServices.swift

@@ -0,0 +1,114 @@
+import Flutter
+import Foundation
+
+/// Pushes upload-batch completions to Dart's `UploadService.completions`.
+final class UploadStatusStreamHandler: NSObject, FlutterStreamHandler {
+  var sink: FlutterEventSink?
+
+  func onListen(withArguments arguments: Any?, eventSink events: @escaping FlutterEventSink)
+    -> FlutterError?
+  {
+    sink = events
+    return nil
+  }
+
+  func onCancel(withArguments arguments: Any?) -> FlutterError? {
+    sink = nil
+    return nil
+  }
+}
+
+/// The iOS side of the `dev.ayushya.noo/*` channels `lib/services/` talks to
+/// (Android's lives in `MainActivity.kt`). Only the upload and download
+/// services are implemented so far; the rest still throw
+/// `MissingPluginException`, which the Dart side treats as "unavailable"
+/// (`lib/services/native_channel.dart`).
+enum NativeServices {
+  private static let uploadStatus = UploadStatusStreamHandler()
+
+  static func register(messenger: FlutterBinaryMessenger) {
+    FlutterMethodChannel(name: "dev.ayushya.noo/upload_service", binaryMessenger: messenger)
+      .setMethodCallHandler { call, result in
+        guard call.method == "startUpload" else { return result(FlutterMethodNotImplemented) }
+        handle(call, result) { args in
+          let files = try parseJSONList(args["files"])
+          try TransferManager.shared.startUpload(
+            serverUrl: try string(args, "serverUrl"),
+            username: try string(args, "username"),
+            authHeader: try string(args, "authHeader"),
+            files: files.compactMap { entry in
+              guard let uri = entry["uri"] as? String, let name = entry["name"] as? String else {
+                return nil
+              }
+              return UploadFile(uri: uri, name: name)
+            },
+            remoteFolder: (args["remoteFolder"] as? String) ?? "/"
+          )
+        }
+      }
+
+    FlutterMethodChannel(name: "dev.ayushya.noo/download_service", binaryMessenger: messenger)
+      .setMethodCallHandler { call, result in
+        guard call.method == "startDownload" else { return result(FlutterMethodNotImplemented) }
+        handle(call, result) { args in
+          let items = try parseJSONList(args["files"])
+          try TransferManager.shared.startDownload(
+            serverUrl: try string(args, "serverUrl"),
+            username: try string(args, "username"),
+            authHeader: try string(args, "authHeader"),
+            items: items.compactMap { entry in
+              guard let path = entry["path"] as? String, let name = entry["name"] as? String else {
+                return nil
+              }
+              return (path: path, name: name)
+            }
+          )
+        }
+      }
+
+    FlutterEventChannel(name: "dev.ayushya.noo/upload_service/status", binaryMessenger: messenger)
+      .setStreamHandler(uploadStatus)
+    TransferManager.shared.onUploadBatchFinished = { folder, succeeded, failed in
+      uploadStatus.sink?(["remoteFolder": folder, "succeeded": succeeded, "failed": failed])
+    }
+    TransferManager.shared.reconnect()
+  }
+
+  // MARK: - Argument helpers
+
+  /// Runs [work] with the call's argument map, turning a thrown error into
+  /// the `FlutterError` Dart's `catch` shows the user.
+  private static func handle(
+    _ call: FlutterMethodCall,
+    _ result: @escaping FlutterResult,
+    work: ([String: Any]) throws -> Void
+  ) {
+    guard let args = call.arguments as? [String: Any] else {
+      return result(FlutterError(code: "bad_args", message: "Missing arguments.", details: nil))
+    }
+    do {
+      try work(args)
+      result(nil)
+    } catch {
+      result(FlutterError(code: "transfer_failed", message: error.localizedDescription, details: nil))
+    }
+  }
+
+  private static func string(_ args: [String: Any], _ key: String) throws -> String {
+    guard let value = args[key] as? String, !value.isEmpty else {
+      throw TransferError(message: "Missing \(key).")
+    }
+    return value
+  }
+
+  /// The Dart services pass their file list as one JSON string.
+  private static func parseJSONList(_ value: Any?) throws -> [[String: Any]] {
+    guard let json = value as? String,
+      let data = json.data(using: .utf8),
+      let list = try JSONSerialization.jsonObject(with: data) as? [[String: Any]]
+    else {
+      throw TransferError(message: "Missing file list.")
+    }
+    return list
+  }
+}