See also: https://phabricator.wikimedia.org/T220402#5133994
We should have an openapi/swagger spec published at /?spec
See: https://swagger.io/docs/specification/about/
TODO: figure out what should be in spec
- Data for /_info
- Data and error codes for /termbox (probably details to be replicated from src/server/app.ts)
Looks like https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/services/mathoid/+/master/spec.yaml could be a good place to judge what we need.