Moving the copilot-sdk cookbook content in here

cookbook/copilot-sdk/dotnet/persisting-sessions.md

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+# Session Persistence and Resumption
+
+Save and restore conversation sessions across application restarts.
+
+## Example scenario
+
+You want users to be able to continue a conversation even after closing and reopening your application.
+
+> **Runnable example:** [recipe/persisting-sessions.cs](recipe/persisting-sessions.cs)
+>
+> ```bash
+> cd recipe
+> dotnet run persisting-sessions.cs
+> ```
+
+### Creating a session with a custom ID
+
+```csharp
+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" });
+
+// Session ID is preserved
+Console.WriteLine(session.SessionId); // "user-123-conversation"
+
+// Destroy session but keep data on disk
+await session.DisposeAsync();
+await client.StopAsync();
+```
+
+### Resuming a session
+
+```csharp
+await using var client = new CopilotClient();
+await client.StartAsync();
+
+// Resume the previous session
+var session = await client.ResumeSessionAsync("user-123-conversation");
+
+// Previous context is restored
+await session.SendAsync(new MessageOptions { Prompt = "What were we discussing?" });
+
+await session.DisposeAsync();
+await client.StopAsync();
+```
+
+### Listing available sessions
+
+```csharp
+var sessions = await client.ListSessionsAsync();
+foreach (var s in sessions)
+{
+    Console.WriteLine($"Session: {s.SessionId}");
+}
+```
+
+### Deleting a session permanently
+
+```csharp
+// Remove session and all its data from disk
+await client.DeleteSessionAsync("user-123-conversation");
+```
+
+### Getting session history
+
+Retrieve all messages from a session:
+
+```csharp
+var messages = await session.GetMessagesAsync();
+foreach (var msg in messages)
+{
+    Console.WriteLine($"[{msg.Type}] {msg.Data.Content}");
+}
+```
+
+## Best practices
+
+1. **Use meaningful session IDs**: Include user ID or context in the session ID
+2. **Handle missing sessions**: Check if a session exists before resuming
+3. **Clean up old sessions**: Periodically delete sessions that are no longer needed