feat(launcher): implement verified atomic updates

tests/AcDream.Launcher.Core.Tests/Updates/UpdateSessionBarrierTests.cs

@@ -0,0 +1,147 @@
+using System.Diagnostics;
+using AcDream.Launcher.Core.Updates;
+
+namespace AcDream.Launcher.Core.Tests.Updates;
+
+public sealed class UpdateSessionBarrierTests : IDisposable
+{
+    private readonly string _root = Path.Combine(
+        Path.GetTempPath(),
+        "acdream-update-lease-tests",
+        Guid.NewGuid().ToString("N"));
+
+    public void Dispose()
+    {
+        if (Directory.Exists(_root))
+        {
+            Directory.Delete(_root, recursive: true);
+        }
+    }
+
+    [Fact]
+    public void SharedSessionsCoexistAndExcludeUpdateTransactions()
+    {
+        var barrier = new UpdateSessionBarrier(_root);
+        using UpdateSessionBarrier.SessionLease first = barrier.AcquireSession();
+        using UpdateSessionBarrier.SessionLease second = barrier.AcquireSession();
+
+        LauncherUpdateException blocked = Assert.Throws<LauncherUpdateException>(
+            barrier.AcquireExclusive);
+
+        Assert.Contains("session", blocked.Message, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public void ExclusiveUpdaterExcludesSessionsAndConcurrentUpdater()
+    {
+        var barrier = new UpdateSessionBarrier(_root);
+        using UpdateSessionBarrier.ExclusiveLease update = barrier.AcquireExclusive();
+
+        Assert.Throws<LauncherUpdateException>(barrier.AcquireSession);
+        Assert.Throws<LauncherUpdateException>(barrier.AcquireExclusive);
+    }
+
+    [Theory]
+    [InlineData("session")]
+    [InlineData("exclusive")]
+    public async Task CrossProcessLeaseRefusesRacingLauncherAndReleasesCleanly(string mode)
+    {
+        string ready = Path.Combine(_root, mode + ".ready");
+        string release = Path.Combine(_root, mode + ".release");
+        Directory.CreateDirectory(_root);
+        string fixture = GetFixturePath();
+        Assert.True(File.Exists(fixture), $"Missing fixture: {fixture}");
+        var startInfo = new ProcessStartInfo("dotnet")
+        {
+            UseShellExecute = false,
+            RedirectStandardError = true,
+            RedirectStandardOutput = true,
+        };
+        startInfo.ArgumentList.Add(fixture);
+        startInfo.ArgumentList.Add("hold-update-lease");
+        startInfo.ArgumentList.Add(mode);
+        startInfo.ArgumentList.Add(_root);
+        startInfo.ArgumentList.Add(ready);
+        startInfo.ArgumentList.Add(release);
+        using Process holder = Process.Start(startInfo)
+            ?? throw new InvalidOperationException("Could not start update lease fixture.");
+        try
+        {
+            await WaitForFileAsync(ready, holder);
+            var barrier = new UpdateSessionBarrier(_root);
+            Assert.Throws<LauncherUpdateException>(barrier.AcquireExclusive);
+            if (mode == "session")
+            {
+                using UpdateSessionBarrier.SessionLease peer = barrier.AcquireSession();
+            }
+            else
+            {
+                Assert.Throws<LauncherUpdateException>(barrier.AcquireSession);
+            }
+
+            await File.WriteAllTextAsync(release, "release");
+            await holder.WaitForExitAsync().WaitAsync(TimeSpan.FromSeconds(10));
+            Assert.Equal(0, holder.ExitCode);
+            using UpdateSessionBarrier.ExclusiveLease after = barrier.AcquireExclusive();
+        }
+        finally
+        {
+            if (!holder.HasExited)
+            {
+                holder.Kill(entireProcessTree: true);
+                await holder.WaitForExitAsync().WaitAsync(TimeSpan.FromSeconds(10));
+            }
+        }
+    }
+
+    private static async Task WaitForFileAsync(string path, Process process)
+    {
+        DateTimeOffset deadline = DateTimeOffset.UtcNow + TimeSpan.FromSeconds(10);
+        while (!File.Exists(path))
+        {
+            if (process.HasExited)
+            {
+                throw new InvalidOperationException(
+                    $"Lease fixture exited early with {process.ExitCode}: "
+                    + await process.StandardError.ReadToEndAsync());
+            }
+
+            if (DateTimeOffset.UtcNow >= deadline)
+            {
+                throw new TimeoutException("Lease fixture did not become ready.");
+            }
+
+            await Task.Delay(20);
+        }
+    }
+
+    private static string GetFixturePath()
+    {
+        string root = FindRepositoryRoot();
+        string configuration = new DirectoryInfo(AppContext.BaseDirectory)
+            .Parent?.Name ?? "Release";
+        return Path.Combine(
+            root,
+            "tests",
+            "AcDream.Launcher.Core.Tests.Fixtures.InstallLeaseHolder",
+            "bin",
+            configuration,
+            "net10.0",
+            "AcDream.Launcher.Core.Tests.Fixtures.InstallLeaseHolder.dll");
+    }
+
+    private static string FindRepositoryRoot()
+    {
+        for (var directory = new DirectoryInfo(AppContext.BaseDirectory);
+             directory is not null;
+             directory = directory.Parent)
+        {
+            if (File.Exists(Path.Combine(directory.FullName, "AcDream.slnx")))
+            {
+                return directory.FullName;
+            }
+        }
+
+        throw new InvalidOperationException("Repository root was not found.");
+    }
+}