This is basically working now.
Because "hint" is designed to be as forgiving as possible, by default the non-presentation of a topic will cause the command to automatically look up the current topic and display it.
This means the shell infrastructure's normal handling of tab is different, as there is no mandatory argument. As with the rest of Roo, TAB will only present options if a mandatory option name is specified, or "--" is specified.
Therefore, to access TAB assist with the "hint" command, one needs to type "hint --TAB TAB". This will expand to "hint --topic" and then the list of options. This is likely to be useful to those who don't want to type the hint topics in by hand.
Git commit f170c196293cbc07ff378b61eee8f5464059527d.