You always have this problem thats why you have a release process for apis.
And monorepo or not, bad software developers will always run into this issue. Most software will not have 'many teams'. Most software is written by a lot of small companies doing niche things. Big software companies with more than one team, normally have release managers.
My tipp: use architecture unit tests for external facing APIs. If you are a smaller company: 24/7 doesn't has to be the thing, just communicate this to your customers but overall if you run SaaS Software and still don't know how to do zero-downtime-deployment in 2025/2026, just do whatever you are still doing because man come on...
And monorepo or not, bad software developers will always run into this issue. Most software will not have 'many teams'. Most software is written by a lot of small companies doing niche things. Big software companies with more than one team, normally have release managers.
My tipp: use architecture unit tests for external facing APIs. If you are a smaller company: 24/7 doesn't has to be the thing, just communicate this to your customers but overall if you run SaaS Software and still don't know how to do zero-downtime-deployment in 2025/2026, just do whatever you are still doing because man come on...