Strictly speaking they’re shared state, but the way you model your application around channels is generally to have independent little chunks of work and the channels are just a means of communicating. I know it’s not one-for-one with Erlang.

You can think of closing the channel as sending a message “there will be no further messages”, the panic on write is enforcement of that contract.

Additionally the safe way to use closing of a channel is the writer closing it. If you have multiple writers, you have to either synchronise them, or don’t close the channel.

You don't have to close a channel in Go and in many cases you actually shouldn't.

Even if you choose to close a channel because it's useful to you, it's not necessarily shared state. In a lot of cases, closing a channel behaves just like a message in its queue.