SessionStartEvent and SessionShutdownEvent never fire via CopilotSession.On for .NET #535

#!/usr/bin/env dotnet
#:package GitHub.Copilot.SDK@0.1.26-preview.0

// Bug repro: SessionStartEvent and SessionShutdownEvent never fire
// when subscribing to CopilotSession events via session.On(...).
//
// This repro addresses potential timing/scoping objections:
//   1. Subscription is created immediately after CreateSessionAsync
//   2. Subscription is kept alive through session disposal (manual dispose order)
//   3. GetMessagesAsync checks the event history independently
//
// SDK version: GitHub.Copilot.SDK 0.1.26-preview.0

using GitHub.Copilot.SDK;

using var client = new CopilotClient();
await client.StartAsync(CancellationToken.None);

string workDir = Path.Combine(Path.GetTempPath(), $"sdk-model-repro-{Guid.NewGuid():N}");
Directory.CreateDirectory(workDir);

try
{
    var config = new SessionConfig
    {
        Model = "claude-sonnet-4",
        WorkingDirectory = workDir,
    };

    Console.WriteLine($"SessionConfig.Model = \"{config.Model}\"");
    Console.WriteLine();

    var receivedEvents = new List<string>();

    // Create session, then subscribe immediately (no gap for missed events)
    var session = await client.CreateSessionAsync(config);
    var sub = session.On(evt =>
    {
        receivedEvents.Add(evt.GetType().Name);

        switch (evt)
        {
            case SessionStartEvent start:
                Console.WriteLine($"[SessionStartEvent]");
                Console.WriteLine($"  SelectedModel = {Quote(start.Data?.SelectedModel)}");
                break;

            case AssistantTurnStartEvent:
                Console.WriteLine($"[AssistantTurnStartEvent]");
                break;

            case AssistantUsageEvent usage:
                Console.WriteLine($"[AssistantUsageEvent]");
                Console.WriteLine($"  Model         = {Quote(usage.Data?.Model)}");
                Console.WriteLine($"  InputTokens   = {usage.Data?.InputTokens}");
                Console.WriteLine($"  OutputTokens  = {usage.Data?.OutputTokens}");
                break;

            case AssistantTurnEndEvent:
                Console.WriteLine($"[AssistantTurnEndEvent]");
                break;

            case SessionShutdownEvent shutdown:
                Console.WriteLine($"[SessionShutdownEvent]");
                Console.WriteLine($"  CurrentModel  = {Quote(shutdown.Data?.CurrentModel)}");
                Console.WriteLine($"  ShutdownType  = {shutdown.Data?.ShutdownType}");
                break;
        }
    });

    Console.WriteLine("Sending prompt...");
    Console.WriteLine();

    try
    {
        await session.SendAndWaitAsync(
            new MessageOptions { Prompt = "Reply with exactly: hello" },
            timeout: TimeSpan.FromMinutes(2));
    }
    catch (Exception ex)
    {
        Console.WriteLine($"SendAndWaitAsync threw: {ex.Message}");
    }

    // Check event history independently of the subscription
    Console.WriteLine();
    Console.WriteLine("--- Event history (GetMessagesAsync) ---");
    var history = await session.GetMessagesAsync(CancellationToken.None);
    foreach (var evt in history)
        Console.WriteLine($"  {evt.GetType().Name}");

    // Dispose session while subscription is still active
    Console.WriteLine();
    Console.WriteLine("--- Disposing session (subscription still active) ---");
    await session.DisposeAsync();
    await Task.Delay(1000); // allow any async event delivery

    // Now dispose subscription
    sub.Dispose();

    // Diagnosis
    Console.WriteLine();
    Console.WriteLine("--- Diagnosis ---");

    var historyTypes = history.Select(e => e.GetType().Name).ToHashSet();

    Console.WriteLine($"SessionStartEvent    in history: {historyTypes.Contains("SessionStartEvent"),-5}  delivered to On(): {receivedEvents.Contains("SessionStartEvent")}");
    Console.WriteLine($"SessionShutdownEvent in history: {historyTypes.Contains("SessionShutdownEvent"),-5}  delivered to On(): {receivedEvents.Contains("SessionShutdownEvent")}");
}
finally
{
    try { Directory.Delete(workDir, recursive: true); } catch { }
}

static string Quote(string? value) => value is null ? "<null>" : $"\"{value}\"";