There are a couple of instances where we'd like to signal that a page doesn't have a summary or that the summary is empty:
- When the page is a disambiguation page (T168391)
We can and should use the Disambiguator extension's API to detect whether or not the page is a disambiguation page.
- When the last sentence from the page's introductory paragraph ends with a ":" (T168328)
Currently, we test whether the extract is empty after some processing is done on the client. This work can and should be done in the page summary API.
We've deferred the decision to pick either the MediaWiki API or RESTBase as the place that we build the page summary API. We need to decide where we're going to move this logic and own that architectural decision.