Stop architectural drift when agents write most code

Your team has shipped fast with coding agents for 2 quarters, and about 70% of new code is now machine-written. Tests pass, but the codebase has drifted: 3 HTTP clients, 2 ways of handling dates, and input checks copied into every handler instead of shared. The pieces no longer fit together.

As the staff engineer, what do you change so next quarter's code converges instead of drifting further?