> You are totally correct that to achieve the same performance, correctness, and overall master level "green"ness in a multirepo system you would have to either define or detect dependencies and dependent repos, build the entire affected chain, and test the result. That part is much easier in monorepo.

You also would need to do that as an atomic operation (in the mono-repo + especially with a commit queue you're building on the atomicity of git).

Having to unwinding that transaction if you aren't atomic can get you into a big mess at larger scales.

Here's a good related talk: C++ as a "Live at Head" language: https://www.youtube.com/watch?v=tISy7EJQPzI by Titus Winters (from Google).