Phase 8: README updates for OnLifecycle<T> and lifecycle event types

Replace stale references to SessionLifecycleEventTypes constants with the
new typed hierarchy (SessionCreatedEvent / SessionDeletedEvent / etc.).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SteveSandersonMS

dotnet/README.md

@@ -153,35 +153,31 @@ Get the ID of the session currently displayed in the TUI. Only available when co
 
 Request the TUI to switch to displaying the specified session. Only available in TUI+server mode.
 
-##### `On(Action<SessionLifecycleEvent> handler): IDisposable`
+##### `OnLifecycle<T>(Action<T> handler): IDisposable where T : SessionLifecycleEvent`
 
-Subscribe to all session lifecycle events. Returns an `IDisposable` that unsubscribes when disposed.
+Subscribe to session lifecycle events. Pass a derived type to filter by kind, or `SessionLifecycleEvent` to receive every lifecycle event. Returns an `IDisposable` that unsubscribes when disposed.
 
 ```csharp
+// Receive every lifecycle event:
 using var subscription = client.OnLifecycle<SessionLifecycleEvent>(evt =>
 {
     Console.WriteLine($"Session {evt.SessionId}: {evt.Type}");
 });
-```
-
-##### `On(string eventType, Action<SessionLifecycleEvent> handler): IDisposable`
 
-Subscribe to a specific lifecycle event type. Use `SessionLifecycleEventTypes` constants.
-
-```csharp
-using var subscription = client.OnLifecycle<SessionForegroundEvent>(evt =>
+// Only receive foreground events:
+using var foreground = client.OnLifecycle<SessionForegroundEvent>(evt =>
 {
     Console.WriteLine($"Session {evt.SessionId} is now in foreground");
 });
 ```
 
 **Lifecycle Event Types:**
 
-- `SessionLifecycleEventTypes.Created` - A new session was created
-- `SessionLifecycleEventTypes.Deleted` - A session was deleted
-- `SessionLifecycleEventTypes.Updated` - A session was updated
-- `SessionLifecycleEventTypes.Foreground` - A session became the foreground session in TUI
-- `SessionLifecycleEventTypes.Background` - A session is no longer the foreground session
+- `SessionCreatedEvent` — A new session was created
+- `SessionDeletedEvent` — A session was deleted
+- `SessionUpdatedEvent` — A session was updated
+- `SessionForegroundEvent` — A session became the foreground session in TUI
+- `SessionBackgroundEvent` — A session is no longer the foreground session
 
 ---
 

dotnet/test/E2E/HookLifecycleAndOutputE2ETests.cs

@@ -3,6 +3,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 using Microsoft.Extensions.AI;
+using System.Text.Json;
 using Xunit;
 using Xunit.Abstractions;
 
@@ -326,7 +327,7 @@ public async Task Should_Allow_PostToolUse_To_Return_ModifiedResult()
                         {
                             TextResultForLlm = "modified by post hook",
                             ResultType = "success",
-                            ToolTelemetry = new Dictionary<string, object>(),
+                            ToolTelemetry = new Dictionary<string, JsonElement>(),
                         },
                         SuppressOutput = false,
                     });