feat(launcher): implement verified atomic updates

src/AcDream.Launcher.Core/Updates/ReleaseManifest.cs

@@ -0,0 +1,37 @@
+namespace AcDream.Launcher.Core.Updates;
+
+public sealed record ReleaseArtifact(Uri Url, string Sha256, long Size);
+
+public sealed record ReleaseManifest(
+    LauncherVersion Version,
+    LauncherVersion MinimumLauncherVersion,
+    IReadOnlyDictionary<string, ReleaseArtifact> Clients,
+    IReadOnlyDictionary<string, ReleaseArtifact> Launchers)
+{
+    public const int CurrentSchemaVersion = 1;
+
+    public ReleaseArtifact RequireClient(string rid) =>
+        Clients.TryGetValue(rid, out ReleaseArtifact? artifact)
+            ? artifact
+            : throw new LauncherUpdateException(
+                $"Release {Version} has no client payload for RID '{rid}'.");
+
+    public ReleaseArtifact RequireLauncher(string rid) =>
+        Launchers.TryGetValue(rid, out ReleaseArtifact? artifact)
+            ? artifact
+            : throw new LauncherUpdateException(
+                $"Release {Version} has no launcher payload for RID '{rid}'.");
+}
+
+public sealed class LauncherUpdateException : Exception
+{
+    public LauncherUpdateException(string message)
+        : base(message)
+    {
+    }
+
+    public LauncherUpdateException(string message, Exception innerException)
+        : base(message, innerException)
+    {
+    }
+}