Add comments clarifying thread-safety

Sources/Containerization/ContainerManager.swift

@@ -45,6 +45,7 @@ public struct ContainerManager: Sendable {
     @available(macOS 26.0, *)
     public struct VmnetNetwork: Network {
         private var allocator: Allocator
+        // `reference` isn't used concurrently.
         nonisolated(unsafe) private let reference: vmnet_network_ref
 
         /// The IPv4 subnet of this network.
@@ -94,6 +95,7 @@ public struct ContainerManager: Sendable {
             public let gateway: String?
             public let macAddress: String?
 
+            // `reference` isn't used concurrently.
             nonisolated(unsafe) private let reference: vmnet_network_ref
 
             public init(
@@ -478,9 +480,4 @@ extension CIDRAddress {
     }
 }
 
-@available(macOS 26.0, *)
-private struct SendableReference: Sendable {
-    nonisolated(unsafe) private let reference: vmnet_network_ref
-}
-
 #endif

Sources/Containerization/NATNetworkInterface.swift

@@ -31,6 +31,7 @@ public final class NATNetworkInterface: Interface, Sendable {
     public let macAddress: String?
 
     @available(macOS 26, *)
+    // `reference` isn't used concurrently.
     public nonisolated(unsafe) let reference: vmnet_network_ref!
 
     @available(macOS 26, *)

Sources/Containerization/UnixSocketRelay.swift

@@ -267,6 +267,7 @@ extension SocketRelay {
             )
         }
 
+        // `buf1` isn't used concurrently.
         nonisolated(unsafe) let buf1 = UnsafeMutableBufferPointer<UInt8>.allocate(capacity: Int(getpagesize()))
         connSource.setEventHandler {
             Self.fdCopyHandler(
@@ -278,6 +279,7 @@ extension SocketRelay {
         }
 
         nonisolated(unsafe) let buf2 = UnsafeMutableBufferPointer<UInt8>.allocate(capacity: Int(getpagesize()))
+        // `buf2` isn't used concurrently.
         vsockConnectionSource.setEventHandler {
             Self.fdCopyHandler(
                 buffer: buf2,

Sources/Containerization/VZVirtualMachineInstance.swift

@@ -68,6 +68,7 @@ struct VZVirtualMachineInstance: VirtualMachineInstance, Sendable {
         }
     }
 
+    // `vm` isn't used concurrently.
     private nonisolated(unsafe) let vm: VZVirtualMachine
     private let queue: DispatchQueue
     private let group: MultiThreadedEventLoopGroup

Sources/ContainerizationOS/AsyncSignalHandler.swift

@@ -53,6 +53,7 @@ public final class AsyncSignalHandler: Sendable {
 
     struct State: Sendable {
         var conts: [AsyncStream<Int32>.Continuation] = []
+        // `sources` isn't used concurrently.
         nonisolated(unsafe) var sources: [any DispatchSourceSignal] = []
     }
 

Sources/Integration/ProcessTests.swift

@@ -62,6 +62,7 @@ extension IntegrationSuite {
     }
 
     final class BufferWriter: Writer {
+        // `data` isn't used concurrently.
         nonisolated(unsafe) var data = Data()
 
         func write(_ data: Data) throws {