Agents are already too good, the models improved

Nowadays you can just start with a plan.md and add everything you want there, verification etc

And you can build a loop to verify/validate it in case its a big/long-running plan

I don't have the problems you mentioned that the models aren't able to follow instructions throughoutly, they do make some mistakes, but it's up to you to set up a process that would work for your codebase to understand that the mistakes were made and need to be fixed, that can be done in a loop for example.