diff --git a/tests/AcDream.Headless.Tests/HeadlessConsoleTests.cs b/tests/AcDream.Headless.Tests/HeadlessConsoleTests.cs
index 4a0b5f45..d8991b58 100644
--- a/tests/AcDream.Headless.Tests/HeadlessConsoleTests.cs
+++ b/tests/AcDream.Headless.Tests/HeadlessConsoleTests.cs
@@ -524,6 +524,51 @@ public sealed class HeadlessConsoleTests
 
     // ── HeadlessProcessHost: end-to-end console wiring ───────────────────
 
+    /// <summary>
+    /// S3: an end-to-end proof that a console line, read from a plain
+    /// <see cref="StringReader"/>, reaches the real session's
+    /// <c>SubmitConsoleLine</c> pipeline through the actual
+    /// <see cref="HeadlessProcessHost"/> wiring (background reader thread →
+    /// per-tick <c>ConsolePump</c> → <c>ChatCommandRouter.Submit</c> → the
+    /// wire), and that <c>/quit</c> ends <see cref="HeadlessProcessHost.RunAsync"/>
+    /// through the SAME graceful path an external cancellation takes —
+    /// <see cref="HeadlessExitCode.Success"/>, not an error code.
+    /// </summary>
+    [Fact]
+    public async Task ConsoleLineReachesTheSessionAndQuitEndsTheProcessGracefully()
+    {
+        var captured = new List<byte[]>();
+        var operations = new FixtureSessionOperations
+        {
+            GameActionCapture = body => captured.Add(body),
+        };
+        var configuration = new HeadlessConfiguration
+        {
+            Version = 1,
+            Sessions = [Descriptor()],
+        };
+        using var diagnostics = new StringWriter();
+        using var input = new System.IO.StringReader(
+            "hello" + Environment.NewLine + "/quit" + Environment.NewLine);
+        using var host = new HeadlessProcessHost(
+            configuration,
+            HeadlessPathSet.Resolve(new HeadlessPathOverrides()),
+            input,
+            diagnostics,
+            operations,
+            new FakeTimeProvider(),
+            directCredentials: new HeadlessDirectCredentials("account", "password"),
+            consoleEnabled: true);
+
+        HeadlessExitCode exitCode = await host.RunAsync(CancellationToken.None)
+            .WaitAsync(TimeSpan.FromSeconds(10));
+
+        Assert.Equal(HeadlessExitCode.Success, exitCode);
+        byte[] body = Assert.Single(captured);
+        Assert.Equal(ChatRequests.TalkOpcode, ActionOpcode(body));
+        Assert.Equal("hello", TalkText(body));
+    }
+
     /// <summary>
     /// S6: <c>standardOutputIsTerminal</c> is threaded in as a constructor
     /// parameter, not read from the real <c>System.Console</c> inside