I'm thinking something like panicking all the goroutines started in a context that's been cancelled, and something like defer to handle cleanup during cancellat

I'm thinking something like panicking all the goroutines started in a context that's been cancelled, and something like defer to handle cleanup during cancellation. Some expression that can read and write a typed value for a key in the current context (not even the standard library can do this without generics). If contexts have to become part of the calling convention, that's fine, just don't add more noise to every function call in the source.