[RT-E6] test: the door refusals and the contender exit head are pinned before RT-E6 rewrites them

tests/OpenCode.Sdk.Tests/Hosting/BackgroundService/Contender/ServiceContenderSpawnerTests.cs

@@ -639,6 +639,8 @@ public async Task TryGetFailure_Should_Report_A_Nonzero_Exit_With_The_Stderr_Tai
             await Assert.That(failure).IsNotNull();
             await Assert.That(failure!.Message).Contains("exited with code 2");
             await Assert.That(failure.Message).Contains("Usage: contender-probe");
+            await Assert.That(failure.Message).StartsWith(
+                "The background service contender (pid " + contender.ProcessId.ToString(CultureInfo.InvariantCulture) + ") exited with code 2.\n");
         }
         finally
         {

tests/OpenCode.Sdk.Tests/Hosting/OpenCodeServerContractTests.cs

@@ -205,6 +205,41 @@ public async Task StartAsync_Should_Refuse_A_Blank_Command_Entry()
             new OpenCodeServerOptions { Command = ["bun", " "] })).Throws<ArgumentException>();
     }
 
+    [Test]
+    [Arguments(false, "OpenCodeServerOptions.Command needs the executable and its leading arguments.")]
+    [Arguments(true, "OpenCodeServerOptions.Command entries cannot be blank.")]
+    public Task StartAsync_Should_Name_The_Refused_Command_And_Its_Options(bool blankEntry, string text) =>
+        AssertOptionsRefusalAsync(
+            async () => await OpenCodeServer.StartAsync(new OpenCodeServerOptions { Command = RefusedCommand(blankEntry) }),
+            text);
+
+    [Test]
+    [Arguments(false, "OpenCodeServerEnsureOptions.Command needs the executable and its leading arguments.")]
+    [Arguments(true, "OpenCodeServerEnsureOptions.Command entries cannot be blank.")]
+    public Task EnsureAsync_Should_Name_The_Refused_Command_And_Its_Options(bool blankEntry, string text) =>
+        AssertOptionsRefusalAsync(
+            async () => await OpenCodeServer.EnsureAsync(new OpenCodeServerEnsureOptions { Command = RefusedCommand(blankEntry) }),
+            text);
+
+    private static string[] RefusedCommand(bool blankEntry) => blankEntry ? ["bun", " "] : [];
+
+    /// <summary>
+    /// The door refuses with exactly <paramref name="text"/> for its public <c>options</c> parameter, in the
+    /// message <see cref="ArgumentException"/> renders on each runtime.
+    /// </summary>
+    private static async Task AssertOptionsRefusalAsync(Func<Task> door, string text)
+    {
+        var failure = await Assert.That(door).Throws<ArgumentException>();
+
+        await Assert.That(failure!.Message).IsEqualTo(
+#if NET
+            text + " (Parameter 'options')");
+#else
+            text + Environment.NewLine + "Parameter name: options");
+#endif
+        await Assert.That(failure.ParamName).IsEqualTo("options");
+    }
+
     [Test]
     public async Task Endpoint_Should_Throw_The_Mock_Seam_Failure_On_A_Bare_Mock()
     {