Why do you say that? I would argue that as long as your tests and interfaces are clearly defined no reason it couldn't scale indefinitely.

Practically there is with Claude Code at least.

Hypothetically, if you codified the architecture as a form of durable meta tests, you might be able to significantly raise the ceiling.

Decomposing to interfaces seems to actually increase architectural entropy instead of decrease it when Claude Code is acting on a code base over a certain size/complexity.