chore: import upstream snapshot with attribution

vminitd/Sources/VminitdCore/PauseCommand.swift

@@ -0,0 +1,82 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 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.
+//===----------------------------------------------------------------------===//
+
+#if os(Linux)
+
+import ArgumentParser
+import Dispatch
+import Logging
+
+#if canImport(Musl)
+import Musl
+private let _exit = Musl.exit
+#elseif canImport(Glibc)
+import Glibc
+private let _exit = Glibc.exit
+#endif
+
+public struct PauseCommand: ParsableCommand {
+    public static let configuration = CommandConfiguration(
+        commandName: "pause",
+        abstract: "Run the pause container"
+    )
+
+    public init() {}
+
+    @OptionGroup var options: LogLevelOption
+
+    public mutating func run() throws {
+        let log = makeLogger(label: "pause", level: options.resolvedLogLevel())
+
+        if getpid() != 1 {
+            log.warning("pause should be the first process")
+        }
+
+        // NOTE: For whatever reason, using signal() for the below causes a swift compiler issue.
+        // Can revert whenever that is understood.
+        let sigintSource = DispatchSource.makeSignalSource(signal: SIGINT)
+        sigintSource.setEventHandler {
+            log.info("Shutting down, got SIGINT")
+            _exit(0)
+        }
+        sigintSource.resume()
+
+        let sigtermSource = DispatchSource.makeSignalSource(signal: SIGTERM)
+        sigtermSource.setEventHandler {
+            log.info("Shutting down, got SIGTERM")
+            _exit(0)
+        }
+        sigtermSource.resume()
+
+        let sigchldSource = DispatchSource.makeSignalSource(signal: SIGCHLD)
+        sigchldSource.setEventHandler {
+            var status: Int32 = 0
+            while waitpid(-1, &status, WNOHANG) > 0 {}
+        }
+        sigchldSource.resume()
+
+        log.info("pause container running, waiting for signals...")
+
+        while true {
+            _ = pause()
+        }
+
+        log.error("Error: infinite loop terminated")
+        _exit(42)
+    }
+}
+
+#endif