Updating implementation to match design changes

I am fully convinced that the design-first approach is superior to generating OAS defs from code. However, I have not yet found a good process, or tool, to keep my controller implementations up to date with my OAS design.

Currently, I can design my API in StopLight and then use the resulting OAS def to generate my controller code, with a tool like swagger-codegen. Generating this code is a one time bootstrap process through. Once created, I have modify the stubs to hook into my existing application. If I make changes to the URI or name of a variable, I have no way to automatically push that change to the implementation.

Does anyone have a good way to keep your server code up to date with design?