That's why I mention having real stable APIs for cross-service interaction, as you can't guarantee that all teams deploy the exact same commit everywhere at once. It is possible but I'd argue that's beyond what a monorepo provides. You can't exactly atomically update your postgres schema and JavaScript backend in one step, regardless of your repo arrangement.

Adding new APIs is always easy. Removing them not so much since other teams may not want to do a new release just to update to your new API schema.