I'm quite happy with the process I've stumbled into:

1) Plan the hell out of everything. Aggressively have multiple agents weigh-in on that plan, in sequential waves. Don't skimp here.

2) Have subagents review every code commit.

3) Create tests for EVERYTHING. If something breaks you want it discovered immediately. Not just unit tests - use golden masters to ensure your UI doesn't break, etc, etc.

Nothing magical, but it gets me to a very stable dev system. And all I have to do is paste those three rules into my agent, and he does it all for me. It's not difficult.