Your AI agent's diff looks fine. That's the problem.

Give an agent a simple task:

Add an optional loyalty discount to retail pricing. Enterprise pricing and the public API must stay unchanged.

Twenty minutes later it's done. Tests are green, the summary is confident. Along the way it also "cleaned up" a shared pricing helper — and in the diff, that looks like diligence, not scope creep.

Here's the uncomfortable part: the diff can't tell you the difference. Did the agent stay inside the intended subsystem? Did it touch the enterprise path? Did it introduce another clone of that helper? Did it modify the public API despite claiming otherwise? A green diff answers none of that.

So you either re-read every agent patch line by line — and lose the speed you adopted agents for — or you trust the checkmark and accumulate structural drift you'll find months later.