check out the branch. if the changes are that risky, the web ui for your repository host is not suitable for reviewing them.

the rest of your issues sound architectural.

if changes are breaking contracts in calling code, that heavily implies that type declarations are not in use, or enumerable values which drive conditional behavior are mistyped as a primitive supertype.

if unit tests are not catching things, that implies the unit tests are asserting trivial things, being written after the implementation to just make cases that pass based on it, or are mocking modules they don't need to. outside of pathological cases the only thing you should be mocking is i/o, and even then that is the textbook use for dependency injection.