I actually read the frontend code much more than the backend code for the project I'm working on.

Backend code I'm fairly comfortable if the tests are good that it works correctly. It's a much more constrained environment. Obviously there can be things like performance issues that creep in or problems when it mocks too much of the environment.

Meanwhile frontend code I have to consider different browsers, screen sizes, a11y issues, and so on, which agents can certainly do but you have to be fairly explicit about it, and they don't always make the best tradeoffs.