Store pending model changes in a queue

Problem/Motivation

Applying a model change to the API the moment an editor adds a field would mean the front end learns about API changes in production. The whole design rests on a queue between the two: the model changes, the API does not, until someone says so.

Proposed resolution

• Storage for pending entries: what changed, which endpoints and structures it affects, what is proposed, who queued it and when.
• Entry kinds: new, removed, type changed, renamed, unmapped field, unmapped paragraph type, convention suggestion, generator conflict.
• Idempotent — rescanning does not duplicate an entry, and an entry whose cause disappeared is withdrawn.
• Survives a cache rebuild and a deployment, because a queue that empties itself is worse than no queue.

Remaining tasks

Everything.