Thank you for finding the bugs! It shouldn't even be possible feed a 5 to a one-bit connector.

Yes I think I shot myself in the foot by designing the connectors so the labels could only be one or two letters. There is no technical reason they couldn't have descriptive labels like "clock" rather than "c". But it would probably require to turn the design "on the side", so the connectors are left-right rather than top-bottom.

I know I miss tests for a few of the levels.

Thanks for the nice words, it is encouraging!