Mild spoilers ahead, but you're reading the solutions thread.
I was just doing some preliminary checking of the data on my phone with Nushell (to see how much my ageing laptop would suffer) when I discovered there weren't any non trivial cases.
Normally I get the test data working before trying the input data, this is definitely teaching me the value of investigating the data before heading down into the code mines.
Unfortunately I can't get the second star yet because I missed a few days.