A custom command can be added like this:

(:add-command (in jwno/context :command-manager) :brew-coffee
   (fn [strength extraction amount]
     # Do the actual brewing here
     ))

Here :brew-coffee is the name of our new command. strength, extraction and amount are the parameters our command can accept. This will overwrite the command registered under the same name, if there's any.

When the command is not needed anymore, you can remove it by passing its name to the :remove-command method from the command manager object:

(:remove-command (in jwno/context :command-manager) :brew-coffee)

Disclaimer: Jwno can not brew your coffee yet. Maybe we can have that in a future version.