I think with enough structure (written rules and good folder layout), poly/monorepos are the way.

https://backnotprop.com/blog/context-monorepos/

  - Better models can keep the drift in check.
  - What's super important these days is having all historical context, historical decision making, prototypes and whatnot.
  - all projects and their worktrees located together
  - all reference docs, code, etc - a folder away

When I ask "what happened to x?" ... the agent has everything it needs to give me that answer. When it plans the next feature it can validate assumptions against previous decions made in my `decisions` folder.