Weigh an agent for a 12-line hot path change

A staff engineer on your team is making a 12-line change to a hot path in the C++ rendering loop. It relies on 2 facts written down nowhere. An upstream stage always zeroes a buffer before this code runs, and the caller already holds a particular lock. A teammate suggests describing it all to an agent and letting the agent write the change.

What does the agent route really cost compared with writing it by hand? Make the call you would defend.