> monorepos can only work well when there is a mechanical tool for ensuring correctness and that refactorings can be done atomically across the whole tree
Isn't a compiler such a tool? I use a statically typed language, and if I would try to do this:
> everything can reach everything else
then there'll be compilation errors.
which is one of the reasons I like microrepos and versioning: you can do refactorings across subtrees. if there's an edge case you want to address later, you can address it later. if you eschew versioning entirely, you effectively have no choice but to do everything all-or-nothing.
I now believe that monorepos can only work well when there is a mechanical tool for ensuring correctness and that refactorings can be done atomically across the whole tree. Infact, it might be necessary to _only_ commit the refactoring operation to the tree and the source itself. That the whole tree is a blockchain of tree edit operations.