Consider an alternative implementation of the https://github.com/a2aproject/a2a-dotnet/blob/main/src/A2A/Server/TaskUpdateEventEnumerator.cs

Some context:

• ...it looks like this should just be a Channel. NotifyEvent would Write into the channel, NotifyFinalEvent would write into the channel and call Complete on it, and GetAsyncEnumerator would just return ReadAllAsync from the channel
• https://www.youtube.com/watch?v=J3IQBI5HVOw
• https://learn.microsoft.com/en-us/dotnet/api/system.net.serversentevents.sseformatter.writeasync?view=net-9.0-pp