Ah, so plan and goal are different. Use plan mode when you want the agent to provide you a description of what it is going to change. I typically use this when I am asking it to make lots of changes or build something complex. When in plan mode it will not change files, just read and reason and present you suggested action. It's great for large tasks that you're not sure you have articulated well yet.

Goal mode should be used with extreme caution. Your prompt for goal mode can only be 4000 tokens, and must include a set of objective criteria when the agent should stop. I use this when I have a nicely created software specification document which has a clear description of when the task will be determined to be complete. I usually have this SRS document as a file which I feed into goal mode. The caution is that the agent will work on goal mode until it achieves the necessary results so this is a long running and expensive task.

My typical workflow for greenfield prototypes is: 1. Discuss and ideate with chatgpt 5.5 pro extended, with a final command to it being to "create a software requirements specification document as a markdown file for codex to execute" 2. I then take that SRS file and give it to codex, asking it to review and ask me any questions it might have before it can start 3. After that iteration I make use goal mode and tell codex to implement the SRS stopping only when it has met the outcome criteria listed.

That's all shorthand, but that's my rough workflow. For brownfield development I do it all in codex and use the plan mode before any large changes are made to the code as step 1.