You don't!
Have you tried adding rules/automations that make it explicit to review and fix the code for bloat (per your taste, with examples if needed)?
With this setup + a good frontier model you will never have to be on the lookout for code bloat. You can even get the agent to send you text message with the LOC-- if it makes you feel better.
I think I understand where you're coming from, that it's hard to "let go" (I've been coding for 30 years and it was hard for me). That's why I'm recommending to have agents write verifiable quantified reports of the things you care about, so you can build up some trust in the agent's work and you don't have to do things by faith.
How do you establish sane patterns when you’re in an exploratory /architectural mode? You could do this in English, sure, but many of us do this more efficiently and precisely in code in a way that lets us be careful, internalize details, and add measurement + QA to ensure it’s adhered to by agents or humans.
I’m not saying to write all the code. I’m saying it’s useful to write 5% of it. Then let an Agent stamp out / rewrite the rest
100% agreed. And it leads to far better LLM output and lower token usage, too, I find.