lightweight variant

CursorLang.Agent.Tests/Windows/SettingsSignalTests.cs

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+using CursorLang.Agent.Windows;
+using CursorLang.Core.Services;
+using CursorLang.Tests.Shared;
+
+namespace CursorLang.Agent.Tests.Windows;
+
+/// <summary>
+/// The one thing the settings window says to the agent.
+/// </summary>
+/// <remarks>
+/// Both halves of it live apart — the message and the window class name in Core, the
+/// window that answers in the agent — and nothing but a matching pair makes it work.
+/// A renamed class or a renamed message would leave the agent showing yesterday's
+/// settings until it is restarted, and nothing else would complain.
+///
+/// The agent's own window is used rather than a stand-in: what is being checked is
+/// that the window the agent really creates is the one the message reaches.
+/// </remarks>
+public sealed class SettingsSignalTests
+{
+    [Fact]
+    public void The_signal_reaches_the_agents_window()
+    {
+        var delivered = 0;
+
+        using AgentWindow window = Pump.Run(() =>
+        {
+            var created = new AgentWindow();
+            created.AddFilter((message, _, _) =>
+            {
+                if (message != SettingsSignal.Message)
+                {
+                    return false;
+                }
+
+                delivered++;
+                return true;
+            });
+
+            return created;
+        });
+
+        Pump.Run(SettingsSignal.NotifyAgent);
+        Pump.Drain();
+
+        Assert.Equal(1, delivered);
+    }
+
+    // Nobody is listening, and that is a normal state of affairs: the settings window
+    // works perfectly well with no agent behind it
+    [Fact]
+    public void Signalling_with_no_agent_running_passes_without_consequence()
+    {
+        Pump.Run(SettingsSignal.NotifyAgent);
+        Pump.Drain();
+    }
+}