carapace supports usage of cobra completions.

IMO it is probably far simpler to specify the ValidArgsFunction attribute for each *cobra.Command instance that requires it, and return completion directives there that carapace then picks up, like so:

ValidArgsFunction: func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
	if build.Flake() {
		return nil, cobra.ShellCompDirectiveFilterDirs
	} else {
		return nil, cobra.ShellCompDirectiveDefault
	}
},

you can adapt as needed for other positional arguments.

This is looking good! Just one small change :}

Thanks for all the changes!