Moving the copilot-sdk cookbook content in here

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

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+# Working with Multiple Sessions
+
+Manage multiple independent conversations simultaneously.
+
+> **Runnable example:** [recipe/multiple-sessions.cs](recipe/multiple-sessions.cs)
+>
+> ```bash
+> dotnet run recipe/multiple-sessions.cs
+> ```
+
+## Example scenario
+
+You need to run multiple conversations in parallel, each with its own context and history.
+
+## C#
+
+```csharp
+using GitHub.Copilot.SDK;
+
+await using var client = new CopilotClient();
+await client.StartAsync();
+
+// Create multiple independent sessions
+var session1 = await client.CreateSessionAsync(new SessionConfig { Model = "gpt-5" });
+var session2 = await client.CreateSessionAsync(new SessionConfig { Model = "gpt-5" });
+var session3 = await client.CreateSessionAsync(new SessionConfig { Model = "claude-sonnet-4.5" });
+
+// Each session maintains its own conversation history
+await session1.SendAsync(new MessageOptions { Prompt = "You are helping with a Python project" });
+await session2.SendAsync(new MessageOptions { Prompt = "You are helping with a TypeScript project" });
+await session3.SendAsync(new MessageOptions { Prompt = "You are helping with a Go project" });
+
+// Follow-up messages stay in their respective contexts
+await session1.SendAsync(new MessageOptions { Prompt = "How do I create a virtual environment?" });
+await session2.SendAsync(new MessageOptions { Prompt = "How do I set up tsconfig?" });
+await session3.SendAsync(new MessageOptions { Prompt = "How do I initialize a module?" });
+
+// Clean up all sessions
+await session1.DisposeAsync();
+await session2.DisposeAsync();
+await session3.DisposeAsync();
+```
+
+## Custom session IDs
+
+Use custom IDs for easier tracking:
+
+```csharp
+var session = await client.CreateSessionAsync(new SessionConfig
+{
+    SessionId = "user-123-chat",
+    Model = "gpt-5"
+});
+
+Console.WriteLine(session.SessionId); // "user-123-chat"
+```
+
+## Listing sessions
+
+```csharp
+var sessions = await client.ListSessionsAsync();
+foreach (var sessionInfo in sessions)
+{
+    Console.WriteLine($"Session: {sessionInfo.SessionId}");
+}
+```
+
+## Deleting sessions
+
+```csharp
+// Delete a specific session
+await client.DeleteSessionAsync("user-123-chat");
+```
+
+## Use cases
+
+- **Multi-user applications**: One session per user
+- **Multi-task workflows**: Separate sessions for different tasks
+- **A/B testing**: Compare responses from different models