Add launcher coordinator IPC and startup reservation

Introduce a launcher coordinator to reserve startup ownership and prevent duplicate host launches. Adds a NamedPipe-based IPC server/client (LauncherCoordinatorIpcServer/Client), coordinator messages/models, and PublicShellStatus/activation types for richer shell reporting. Enhances StartupAttemptRecord and StartupAttemptRegistry to track coordinator pid/pipe, heartbeat, reserved-before-host-start, and public IPC status, plus new reservation/heartbeat APIs and takeover logic. Wire coordinator into App and LauncherFlowCoordinator to attach secondary launchers, publish coordinator status, probe existing hosts, and include more detailed launch result details. Also adds unit tests and docs describing coordinator and startup visuals behavior.

LanMountainDesktop.Tests/LauncherCoordinatorRegistryTests.cs

@@ -0,0 +1,126 @@
+using System.Text.Json.Nodes;
+using LanMountainDesktop.Launcher.Models;
+using LanMountainDesktop.Launcher.Services;
+using LanMountainDesktop.Shared.Contracts.Launcher;
+using Xunit;
+
+namespace LanMountainDesktop.Tests;
+
+public sealed class LauncherCoordinatorRegistryTests
+{
+    [Fact]
+    public void TryReserveCoordinator_WhenActiveCoordinatorExists_ReturnsActiveAttempt()
+    {
+        using var temp = TemporaryAttemptState.Create();
+        var firstRegistry = new StartupAttemptRegistry(temp.StatePath);
+        var secondRegistry = new StartupAttemptRegistry(temp.StatePath);
+
+        Assert.True(firstRegistry.TryReserveCoordinator(
+            "normal",
+            "Foreground",
+            "pipe-a",
+            out var firstAttempt,
+            out var firstActive));
+        Assert.Null(firstActive);
+
+        Assert.False(secondRegistry.TryReserveCoordinator(
+            "normal",
+            "Foreground",
+            "pipe-b",
+            out _,
+            out var secondActive));
+
+        Assert.NotNull(secondActive);
+        Assert.Equal(firstAttempt.AttemptId, secondActive.AttemptId);
+        Assert.Equal("pipe-a", secondActive.CoordinatorPipeName);
+        Assert.Equal(Environment.ProcessId, secondActive.CoordinatorPid);
+    }
+
+    [Fact]
+    public void TryReserveCoordinator_WhenHeartbeatIsStale_TakesOverAttempt()
+    {
+        using var temp = TemporaryAttemptState.Create();
+        var firstRegistry = new StartupAttemptRegistry(temp.StatePath);
+        var secondRegistry = new StartupAttemptRegistry(temp.StatePath);
+
+        Assert.True(firstRegistry.TryReserveCoordinator(
+            "normal",
+            "Foreground",
+            "pipe-a",
+            out var firstAttempt,
+            out _));
+        temp.SetHeartbeat(DateTimeOffset.UtcNow.AddSeconds(-30));
+
+        Assert.True(secondRegistry.TryReserveCoordinator(
+            "normal",
+            "Foreground",
+            "pipe-b",
+            out var reservedAttempt,
+            out var activeAttempt));
+
+        Assert.Null(activeAttempt);
+        Assert.Equal(firstAttempt.AttemptId, reservedAttempt.AttemptId);
+        Assert.Equal("pipe-b", reservedAttempt.CoordinatorPipeName);
+    }
+
+    [Fact]
+    public void AssignOwnedHostProcess_ClearsReservedBeforeHostStart()
+    {
+        using var temp = TemporaryAttemptState.Create();
+        var registry = new StartupAttemptRegistry(temp.StatePath);
+
+        Assert.True(registry.TryReserveCoordinator(
+            "normal",
+            "Foreground",
+            "pipe-a",
+            out var reservedAttempt,
+            out _));
+        Assert.True(reservedAttempt.ReservedBeforeHostStart);
+
+        var assignedAttempt = registry.AssignOwnedHostProcess(
+            Environment.ProcessId,
+            StartupStage.Initializing,
+            "host assigned");
+
+        Assert.Equal(Environment.ProcessId, assignedAttempt.HostPid);
+        Assert.False(assignedAttempt.ReservedBeforeHostStart);
+    }
+
+    private sealed class TemporaryAttemptState : IDisposable
+    {
+        private TemporaryAttemptState(string directory)
+        {
+            Directory = directory;
+            StatePath = Path.Combine(directory, "startup-attempt.json");
+        }
+
+        public string Directory { get; }
+
+        public string StatePath { get; }
+
+        public static TemporaryAttemptState Create()
+        {
+            var directory = Path.Combine(
+                Path.GetTempPath(),
+                "LanMountainDesktop.LauncherCoordinatorTests",
+                Guid.NewGuid().ToString("N"));
+            System.IO.Directory.CreateDirectory(directory);
+            return new TemporaryAttemptState(directory);
+        }
+
+        public void SetHeartbeat(DateTimeOffset heartbeatAtUtc)
+        {
+            var node = JsonNode.Parse(File.ReadAllText(StatePath))!.AsObject();
+            node["heartbeatAtUtc"] = heartbeatAtUtc.ToString("O");
+            File.WriteAllText(StatePath, node.ToJsonString());
+        }
+
+        public void Dispose()
+        {
+            if (System.IO.Directory.Exists(Directory))
+            {
+                System.IO.Directory.Delete(Directory, recursive: true);
+            }
+        }
+    }
+}