feat(releases): add SelfUpdater.DownloadAndVerifyAsync

src/ClaudeDo.Releases/SelfUpdater.cs

@@ -1,3 +1,4 @@
+using System.IO;
 using System.Net.Http;
 using System.Text.RegularExpressions;
 
@@ -92,4 +93,34 @@ public static partial class SelfUpdater
         File.Copy(currentExePath, oldPath, overwrite: false);
         return launchProcess(oldPath);
     }
+
+    public static async Task<string?> DownloadAndVerifyAsync(
+        IReleaseClient releases,
+        ReleaseAsset installerAsset,
+        ReleaseAsset checksumsAsset,
+        string tempDir,
+        IProgress<long> progress,
+        CancellationToken ct)
+    {
+        Directory.CreateDirectory(tempDir);
+        var installerPath = Path.Combine(tempDir, installerAsset.Name);
+        var checksumsPath = Path.Combine(tempDir, "checksums.txt");
+
+        try
+        {
+            await releases.DownloadAsync(installerAsset.BrowserDownloadUrl, installerPath, progress, ct);
+            await releases.DownloadAsync(checksumsAsset.BrowserDownloadUrl, checksumsPath, new Progress<long>(_ => { }), ct);
+        }
+        catch (Exception ex) when (ex is HttpRequestException or IOException or TaskCanceledException)
+        {
+            return null;
+        }
+
+        var checksumsText = await File.ReadAllTextAsync(checksumsPath, ct);
+        var map = ChecksumVerifier.ParseChecksumsFile(checksumsText);
+        if (!map.TryGetValue(installerAsset.Name, out var expected))
+            return null;
+
+        return ChecksumVerifier.Verify(installerPath, expected) ? installerPath : null;
+    }
 }