I'm in CET so time-wise it can be ok - problems open at 6am meaning if I get up I have about an hour around before I need to walk my walk my dog and get ready for work. But switching on at that time is really hard, the amount of stupid off-by-one errors, or referring to since-renamed-but-still-present functions in my Jupyter Notebook is not even funny.

But I luckily managed to avoid the "reusable AoC library" problem around 2019 when a week beforehand I wrote down the sort of functions I wanted to have at my disposal (usually things around representing 2D/3D grids of unknown size and pathfinding/debugging therein, but a few other bits and pieces) and made a simple library that I will sometimes add things to after I'm done with the problem for the day.

I was tempted to some functions (similar to those your CLI harness provided) for retrieving test data and submitting answers but I managed to stop myself short of that! But I am sure you're far from the only one to end up down that road.