Warnings breaking builds is something you should opt in to with the knowledge that warnings are not part of the fixed public API of the thing you're building against/using as a dependency.

That's the whole point of warnings in the first place - they're a way to communicate that people might be doing something wrong, without hard failing their builds. Otherwise what would be the difference between a warning and an error?

Likewise, opting in to warnings as failures in your build system is a perfectly reasonable decision if you want to be strict about quality, and catch potential issues early. But the fix for a warning you don't want to treat as a warning is to just suppress it somehow (or fix it anyway if it isn't a complete false positive), not demand the maintainer remove it.

(Note I'm just replying to the context of your TLDR, not the whole situation, which I haven't read through yet.)