Stylus is not available via the Android AMO site, but I have been using it for months in both Fennec Release and Beta.
Is this the appropriate place to report such an issue?
Possibly the developer needs to check the Android box during upload of a future version.
I suggested as much to the dev.
The response was somewhat vague, as I recall.
Is the interface for selecting supported platforms something that the dev has to look for when uploading, or is it very straight forward?
This is a screenshot from the page you upload a new version on:
So yes, very straight forward.