feat(releases): add SelfUpdater.HandleReplaceSelfAsync

tests/ClaudeDo.Releases.Tests/SelfUpdaterTests.cs

@@ -124,3 +124,56 @@ public class SelfUpdaterDecisionTests
         Assert.Equal(SelfUpdateDecisionKind.NoUpdate, d.Kind);
     }
 }
+
+public class SelfUpdaterReplaceSelfTests : IDisposable
+{
+    private readonly string _tempDir;
+
+    public SelfUpdaterReplaceSelfTests()
+    {
+        _tempDir = Path.Combine(Path.GetTempPath(), "ClaudeDo.Releases.Tests-" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(_tempDir);
+    }
+
+    public void Dispose() { try { Directory.Delete(_tempDir, true); } catch { } }
+
+    [Fact]
+    public async Task Replace_DeletesOldAndCopiesCurrent()
+    {
+        var oldPath = Path.Combine(_tempDir, "old.exe");
+        var currentPath = Path.Combine(_tempDir, "current.exe");
+        await File.WriteAllTextAsync(oldPath, "OLD");
+        await File.WriteAllTextAsync(currentPath, "NEW");
+
+        var relaunchedWith = "";
+        var result = await SelfUpdater.HandleReplaceSelfAsync(
+            oldPath: oldPath,
+            currentExePath: currentPath,
+            launchProcess: path => { relaunchedWith = path; return true; },
+            maxWaitMs: 500);
+
+        Assert.True(result);
+        Assert.Equal(oldPath, relaunchedWith);
+        Assert.Equal("NEW", await File.ReadAllTextAsync(oldPath));
+    }
+
+    [Fact]
+    public async Task Replace_TimesOutWhenFileStaysLocked_ReturnsFalse()
+    {
+        var oldPath = Path.Combine(_tempDir, "locked.exe");
+        var currentPath = Path.Combine(_tempDir, "current.exe");
+        await File.WriteAllTextAsync(oldPath, "OLD");
+        await File.WriteAllTextAsync(currentPath, "NEW");
+
+        // Hold an exclusive lock across the wait window.
+        using var lockStream = new FileStream(oldPath, FileMode.Open, FileAccess.ReadWrite, FileShare.None);
+
+        var result = await SelfUpdater.HandleReplaceSelfAsync(
+            oldPath: oldPath,
+            currentExePath: currentPath,
+            launchProcess: _ => true,
+            maxWaitMs: 200);
+
+        Assert.False(result);
+    }
+}