Don't spawn a default environment upfront.
This ensures we reply to "kernel_info_request" in a timely fashion, and that we don't spawn a useless environment. It also allows the user to not repeat ";;guix run my-env" in subsequent cells since the default environment is now recorded across cells. * guix-jupyter-kernel.scm (%default-environment-property): New variable. (proxy-state-default-environment, set-proxy-state-default-environment): New procedures. (create-environment): Call 'set-proxy-state-default-environment'. (reply-execute-request): Use the environment returned by 'proxy-state-default-environment'. Print an error as HTML when it's false. <top level>: Remove call to 'start-container' for the "default" environment.