You forgot: "The code is now 100% production ready. All features implemented."
It confidently says this without testing anything or running it.
Placeholder code everywhere, features missing, overall the code ends up not compiling due to the dumbest errors imaginable.
From time to time, go into Opus planning mode, have it review your entire codebase and tell it to go file by file and look for bugs, security issues, logical problems, etc.
Have it make a list. Then load up the context + task list...
Load up the context with your information + task list (broken down into phases).
Have Sonnet implement phase one tasks and mark phase 1 as done. Go into planning mode, have Opus review the work (you should ideally also review it at this point).
Double press escape and go back to the point in the conversation where you loaded up the context with your information + task list.
Tell it to do phase 2.
Repeat until you run out of usage.