For the initial release (https://phabricator.wikimedia.org/T1228), let's lock down the subset of endpoints we intend to open to the public, and document them sufficiently well that a user can consume them without needing knowledge of the underlying code.

There are a few forms that this might take, such as a Swagger spec with a Swagger-UI instance in front of it, or a simple static documentation published on a wiki somewhere.