Pretty minor, but iron pipes shouldn't be allowed to be directed to objects that can only output items. This works fine for e.g. the mining well, but doesn't for the quarry.

How does this not work? I don't have one setup like this personally, but I would assume this would mean you could run a pipeline directly adjacent to a quarry and have no items even attempt to go towards the quarry and spill into the world.

yup

Pipes connects to quarry to get the output. This is just a minor fix to the iron pipe that should indeed get the input, but not try to send to it. No emergency, that can wait.

Well if you remove IInventory (via IBuilderInventory) and implement IPipeConnection it would solve it as well without a hard coded entry for the Quarry.

Once IInventory is gone, the Iron Pipe should no longer see the Quarry as a valid target. IPipeConnection can then be used to make the pipe appear to connect to the Quarry again.

The first question that needs to be asked, "why do pipes even connect to the quarry?" Once you can answer that question, then you can make use of the existing API connection override interfaces to make it "look" like pipes attach to it. Or something...

Upon review, this change appears that it will have to wait until the Builder branch changes are merged in, because it requires removing IBuilderInventory from the Quarry. Which breaks the Quarry's ability to build the frame.

This interface is will be removed in the future anyway.