DSL builder for a CommandNode: declare static choices, dynamic completions and an executes body.
Adds a literal completion value with no further arguments.
Adds a literal completion value with a nested sub-tree built by block.
Adds a runtime-computed set of completions from provider.
Adds runtime completions from provider with a nested sub-tree (for the next argument) via block.
Sets the executor run when the command ends at this node; receiver is the sender, param the args.