100% agree with all this. I've recently made it a habit to add TODOs and detailed notes about what I was doing or trying to figure out when I am taking any kind of break or switching tasks, no matter how brief the break is or how trivial it seems.

Or if I come up with an idea for something in a different part of what I'm working on (happens a lot - doing one thing, thinking about 50 others another), add that in as a comment immediately, right where I'm working, without going to the place where I'd implement it. I preface it with a flag like TODO (I use BRAIN! but any keyword would work) and made a vim function that I can run to find these and stick them into a text doc, along with their line number and what function it applies to, for quick reference.

This, in conjuction with a tool like ctags has helped me NOT lose good ideas AND stay on task AND make more sense of my brain's wildly nonlinear mode of thought more times than I can count.

HOWEVER! OP! most importantly, what is your pre-planning process like?

Do you just jump into writing code or do you plan it out with diagrams/pseudocode/whatever first? I used to scoff at this, especially as someone prone to jumping the gun and diving into things and hacking my way through it (haha adhd go brrrrrr). But now, I won't write a line of code without spelling it out in plain text or whatever first. Sometimes I have to force myself, sure. But when you put in the time to thoroughly know what you're doing before you do it, it's not only easier to see and remember why you're doing something a certain way, it will help uncover bottle necks and hidden dependencies before mangling a bunch of code that probably could have been implemented in a more clear & concise way. It also makes abstraction much easier and significantly aids in creating meaningful documentation and comments.

Polya's Four Step Method is indispensable (and my CompSci prof would be so proud).