I do it during tests. Since I'm already spawning a TestHost and trying out various API calls, one of these tests basically does "curl $host/openapi/openapi.jso

I do it during tests. Since I'm already spawning a TestHost and trying out various API calls, one of these tests basically does "curl $host/openapi/openapi.json | diff ./docs/openapi.json". If it spots a change and fails the test, I check that the difference is expected, and if so I temporarily enable and run a different "test" which actually writes the updated file.