How do you control the development of independent libraries so that there's no incompatibility problems? Really, people have been solving this exact problem for decades. The fact that you changed a word there for something more specific does not change the world.
The answer, of course, is that you version it. Not put in version control, but manually assign version numbers to it.
You try to make it possible to use several versions at the same time, but that's not always possible. If you have to use only one version, make sure to not make any incompatible changes in a single step, first you deprecate old functionality, some time later you remove it. Some times that's impossible, it's natural but it'll hurt anyway, keep those times at a minimum.
Also, make sure you mark your versions differently for features added and incompatible changes, so that developers can express things like "I'll need an API newer enough for implementing feature X, but old enough so that feature Y is still there".
The answer, of course, is that you version it. Not put in version control, but manually assign version numbers to it.
You try to make it possible to use several versions at the same time, but that's not always possible. If you have to use only one version, make sure to not make any incompatible changes in a single step, first you deprecate old functionality, some time later you remove it. Some times that's impossible, it's natural but it'll hurt anyway, keep those times at a minimum.
Also, make sure you mark your versions differently for features added and incompatible changes, so that developers can express things like "I'll need an API newer enough for implementing feature X, but old enough so that feature Y is still there".