That worked. I reiterate for future reference.
Dear Future Programmer,
Contrary to the statement on its NPM reference page, steal-less is not built into steal. Further, it does not get included in a project in the same was as other plugins, i.e., "--save-dev" not "--save" and no "import steal-less from 'blah/path/'.
Instead, you need to first install as a dev dependency:
npm steal-less --save-dev
Then you need to edit your package.json manually to add this:
(It's worth noting that the migration page mentioned above calls for this to be a "system" property. Later in the doc though, it says that "system" is deprecated in favor of "steal". "steal" works. .less is available and the steal-tools build process likes it.)
After these, the connection to less is conducted behind the scenes. No specific 'import' or other reference is needed. The system detects the file extension and does good things automatically. I am able to get full .less goodness with this call...
...to style my application.
In case it's helpful, this is how my package.json looks right now...