Fix foreground process signal forwarding

Sources/Services/ContainerAPIService/Client/ClientProcess.swift

@@ -36,7 +36,7 @@ public protocol ClientProcess: Sendable {
     func resize(_ size: Terminal.Size) async throws
     /// Send a signal to the process `id`.
     /// Kill does not wait for the process to exit, it only delivers the signal.
-    func kill(_ signal: Int32) async throws
+    func kill(_ signal: String) async throws
     ///  Wait for the process `id` to complete and return its exit code.
     /// This method blocks until the process exits and the code is obtained.
     func wait() async throws -> Int32
@@ -76,11 +76,11 @@ struct ClientProcessImpl: ClientProcess, Sendable {
     }
 
     /// Send a signal to the process.
-    public func kill(_ signal: Int32) async throws {
+    public func kill(_ signal: String) async throws {
         let request = XPCMessage(route: .containerKill)
         request.set(key: .id, value: containerId)
         request.set(key: .processIdentifier, value: id)
-        request.set(key: .signal, value: Int64(signal))
+        request.set(key: .signal, value: signal)
 
         try await xpcClient.send(request)
     }

Sources/Services/ContainerAPIService/Client/ProcessIO.swift

@@ -30,9 +30,23 @@ public struct ProcessIO: Sendable {
         SIGINT,
         SIGUSR1,
         SIGUSR2,
-        SIGWINCH,
     ]
 
+    static func signalName(_ signal: Int32) -> String {
+        switch signal {
+        case SIGTERM:
+            "SIGTERM"
+        case SIGINT:
+            "SIGINT"
+        case SIGUSR1:
+            "SIGUSR1"
+        case SIGUSR2:
+            "SIGUSR2"
+        default:
+            "\(signal)"
+        }
+    }
+
     public struct IoTracker: Sendable {
         let stream: AsyncStream<Void>
         let cont: AsyncStream<Void>.Continuation
@@ -198,7 +212,7 @@ public struct ProcessIO: Sendable {
                 _ = group.addTaskUnlessCancelled {
                     for await sig in signals.signals {
                         do {
-                            try await process.kill(sig)
+                            try await process.kill(Self.signalName(sig))
                         } catch {
                             log.error(
                                 "failed to send signal",

Tests/ContainerAPIClientTests/ProcessIOTests.swift

@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+// 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.
+//===----------------------------------------------------------------------===//
+
+import Darwin
+import Testing
+
+@testable import ContainerAPIClient
+
+struct ProcessIOTests {
+    @Test("Forwarded process signals are encoded as names")
+    func forwardedSignalNames() {
+        #expect(ProcessIO.signalName(SIGTERM) == "SIGTERM")
+        #expect(ProcessIO.signalName(SIGINT) == "SIGINT")
+        #expect(ProcessIO.signalName(SIGUSR1) == "SIGUSR1")
+        #expect(ProcessIO.signalName(SIGUSR2) == "SIGUSR2")
+    }
+
+    @Test("Terminal resize signal is handled by the resize path")
+    func terminalResizeSignalIsNotForwardedAsKill() {
+        #expect(!ProcessIO.signalSet.contains(SIGWINCH))
+    }
+}