chore: import upstream snapshot with attribution

Sources/ContainerBuild/BuildStdio.swift

@@ -0,0 +1,70 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025-2026 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 ContainerizationOS
+import Foundation
+import GRPCCore
+import NIO
+
+actor BuildStdio: BuildPipelineHandler {
+    public let quiet: Bool
+    public let handle: FileHandle
+
+    init(quiet: Bool = false, output: FileHandle = FileHandle.standardError) throws {
+        self.quiet = quiet
+        self.handle = output
+    }
+
+    nonisolated func accept(_ packet: ServerStream) throws -> Bool {
+        guard let _ = packet.getIO() else {
+            return false
+        }
+        return true
+    }
+
+    func handle(_ sender: AsyncStream<ClientStream>.Continuation, _ packet: ServerStream) async throws {
+        guard !quiet else {
+            return
+        }
+        guard let io = packet.getIO() else {
+            throw Error.ioMissing
+        }
+        if let cmdString = try TerminalCommand().json() {
+            var response = ClientStream()
+            response.buildID = packet.buildID
+            response.command = .init()
+            response.command.id = packet.buildID
+            response.command.command = cmdString
+            sender.yield(response)
+        }
+        handle.write(io.data)
+    }
+}
+
+extension BuildStdio {
+    enum Error: Swift.Error, CustomStringConvertible {
+        case ioMissing
+        case invalidContinuation
+        var description: String {
+            switch self {
+            case .ioMissing:
+                return "io field missing in packet"
+            case .invalidContinuation:
+                return "continuation could not created"
+            }
+        }
+    }
+}