Moving the copilot-sdk cookbook content in here

cookbook/copilot-sdk/dotnet/recipe/persisting-sessions.cs

@@ -0,0 +1,38 @@
+#:package GitHub.Copilot.SDK@*
+#:property PublishAot=false
+
+using GitHub.Copilot.SDK;
+
+await using var client = new CopilotClient();
+await client.StartAsync();
+
+// Create session with a memorable ID
+var session = await client.CreateSessionAsync(new SessionConfig
+{
+    SessionId = "user-123-conversation",
+    Model = "gpt-5"
+});
+
+await session.SendAsync(new MessageOptions { Prompt = "Let's discuss TypeScript generics" });
+Console.WriteLine($"Session created: {session.SessionId}");
+
+// Destroy session but keep data on disk
+await session.DisposeAsync();
+Console.WriteLine("Session destroyed (state persisted)");
+
+// Resume the previous session
+var resumed = await client.ResumeSessionAsync("user-123-conversation");
+Console.WriteLine($"Resumed: {resumed.SessionId}");
+
+await resumed.SendAsync(new MessageOptions { Prompt = "What were we discussing?" });
+
+// List sessions
+var sessions = await client.ListSessionsAsync();
+Console.WriteLine("Sessions: " + string.Join(", ", sessions.Select(s => s.SessionId)));
+
+// Delete session permanently
+await client.DeleteSessionAsync("user-123-conversation");
+Console.WriteLine("Session deleted");
+
+await resumed.DisposeAsync();
+await client.StopAsync();