The endpoint is a contract someone has to keep for years.
[ trace // field response ]
An API endpoint is a contract. The moment a third party starts using it, you owe them backward compatibility for as long as that third party exists, even if your roadmap would prefer otherwise. The endpoint is a hostage of its own success.
This is why versioning matters and why breaking changes deserve a louder announcement than features. The cost is borne by every integrator, distributed across every codebase that ever called the URL.
Design endpoints to outlast the team that shipped them. The team rotates. The clients do not.
