I don't understand why people are making this so complicated. We have a battle tested SDLC. We don't need to reinvent this shit. We just need to make some affordances in the tools and processes we set up for the majority of the actors in the system to be agents (such as rationing human attention).

Spec your software like an architect/po, decompose it into a task dag, then orchestrate for each lane and assemble all change sets in a merge branch rather than constantly repointing head.