chore: import upstream snapshot with attribution

Sources/Containerization/IO/ReaderStream.swift

@@ -0,0 +1,22 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025-2026 Apple Inc. and the Containerization 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 Foundation
+
+/// A type that returns a stream of Data.
+public protocol ReaderStream: Sendable {
+    func stream() -> AsyncStream<Data>
+}

Sources/Containerization/IO/Terminal+ReaderStream.swift

@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025-2026 Apple Inc. and the Containerization 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 ContainerizationOS
+import Foundation
+
+extension Terminal: ReaderStream {
+    public func stream() -> AsyncStream<Data> {
+        .init { cont in
+            self.handle.readabilityHandler = { handle in
+                let data = handle.availableData
+                if data.isEmpty {
+                    self.handle.readabilityHandler = nil
+                    cont.finish()
+                    return
+                }
+                cont.yield(data)
+            }
+        }
+    }
+}
+
+extension Terminal: Writer {}

Sources/Containerization/IO/Writer.swift

@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025-2026 Apple Inc. and the Containerization 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 Foundation
+
+/// A type that writes the provided Data.
+public protocol Writer: Sendable {
+    func write(_ data: Data) throws
+    func close() throws
+}