chore: import upstream snapshot with attribution

Sources/ContainerResource/Common/ApplicationError.swift

@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+// 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.
+//===----------------------------------------------------------------------===//
+
+/// Protocol for errors with a stable code and structured metadata.
+/// This allows the client to present the error as it chooses.
+
+import OrderedCollections
+
+public protocol AppError: Error {
+    var code: AppErrorCode { get }
+    var metadata: OrderedDictionary<String, String> { get }
+    var underlyingError: Error? { get }
+}
+
+public struct AppErrorCode: RawRepresentable, Hashable, Sendable {
+    public let rawValue: String
+
+    public init(rawValue: String) {
+        self.rawValue = rawValue
+    }
+
+    public static let invalidArgument = AppErrorCode(rawValue: "invalid_argument")
+}