I didn’t understand this part. You said you reviewed the code and it was looking good, so how did the cruft creep in? Were you reviewing every diff, or taking an occasional sample?
I use templates / conventions and make the AI generate code using them. When reviewing code I'm scanning if a file uses a specific template and follows specific conventions.
This can't catch subtle errors like a function is re-created vs is re-used (duplicate code), unnecessary code (bloat), inconsistent naming (a Button component has a cssRow() styling function associated vs cssButton()).
When you start editing, using code these little things add up, consume your attention, drain you up, giving no flow and resulting in minimal productivity.
Looking at the individual changes in isolation, it's harder to see it doesn't match other conventions, duplicates code, removes or disables paths without cleaning up, etc. I'll bet there's also some crazy spaghetti code in there, from helping a co-worker clean up their Ai-generated code that they didn't understand.