I used to work for Firebase, this is a common problem. For my own developer focussed startup I have prevented functions from calling each other to an unbounded depth, exactly so this footgun is removed.

The technical details is outbound requests is given a role encoded in the user-agent, and then I can easily filter out incoming requests by user-agents [1].

[1] https://observablehq.com/@endpointservices/webcode-docs#opti... (see loop prevention flags)