But with GPT 5.6 Sol, I'm still finding that the model makes conceptual mistakes, or gets edge cases wrong, or assumes incorrectly (making an ass out of both user and model). In many cases, I need to at least refine the proposed approach, or amend, correct, or flat out just stop and start over. Not planning and catching these errors, and just letting the agents code their code, would mean I'd have to rollback and redo many times. What a waste!
For a current project, which is ~33k lines of code, I'm also finding that I know the codebase better than the model, and that's vital at the planning stages too. If I wasn't in the planning loop, the model would have reinvented various wheels a few times over. How much spaghetti do you want with your code?
As always, I may simply be doing this wrong. But I'm personally not convinced that the plan is dead, or that I want the plan to be dead. Planning is also good for me -- it keeps me thinking about the code, prompting better, guiding the model better.
If I'm no longer on top of the codebase, then at some point my prompts will devolve to "Do the thing with the thing, that does thing". And I don't want that.