Reproduction

Start the server

$ cd server
$ go run main.go

By default the server accepts up to 64 concurrent h2 steams on a single connection.

Start the proxy

$ cd proxy
$ cargo run

The proxy configures the peer with 100 initial concurrent streams and doesn't limit the number of streams from a downstream client.

Start the client

$ cd client
$ go run main.go

The client attempts to open 100 concurrent streams on a single connection, but fails once 64 streams are opened.