chore: import upstream snapshot with attribution

Sources/Services/RuntimeLinux/Server/NonisolatedInterfaceStrategy.swift

@@ -0,0 +1,56 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2026 Apple Inc. and the container project authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import ContainerResource
+import ContainerRuntimeClient
+import ContainerXPC
+import Containerization
+import ContainerizationError
+import Logging
+import Virtualization
+import vmnet
+
+/// Interface strategy for containers that use macOS's custom network feature.
+@available(macOS 26, *)
+public struct NonisolatedInterfaceStrategy: InterfaceStrategy {
+    private let log: Logger
+
+    public init(log: Logger) {
+        self.log = log
+    }
+
+    public func toInterface(attachment: Attachment, interfaceIndex: Int, additionalData: XPCMessage?) throws -> Interface {
+        guard let additionalData else {
+            throw ContainerizationError(.invalidState, message: "network state does not contain custom network reference")
+        }
+
+        var status: vmnet_return_t = .VMNET_SUCCESS
+        guard let networkRef = vmnet_network_create_with_serialization(additionalData.underlying, &status) else {
+            throw ContainerizationError(.invalidState, message: "cannot deserialize custom network reference, status \(status)")
+        }
+
+        log.info("creating NATNetworkInterface with network reference")
+        let ipv4Gateway = interfaceIndex == 0 ? attachment.ipv4Gateway : nil
+        return NATNetworkInterface(
+            ipv4Address: attachment.ipv4Address,
+            ipv4Gateway: ipv4Gateway,
+            reference: networkRef,
+            macAddress: attachment.macAddress,
+            // https://github.com/apple/containerization/pull/38
+            mtu: attachment.mtu ?? 1280
+        )
+    }
+}