Add an explicit migration step to compare generated OpenAPI and SDK output after each HttpApi slice so we record whether any diff is a real contract change or only acceptable schema churn.
Add a route-by-route inventory for the instance server surface, record which groups are already migrated, and identify the next likely HttpApi candidates and the routes to defer.
Document how auth, instance lookup, and error mapping should continue to compose around the first parallel HttpApi slices so the next migrations can follow the same boundary pattern.
Capture the reusable pattern from the question HttpApi spike and turn the follow-up work into a checklist so the next route-group migrations can follow the same shape.
Kit Langton