Sorry, left out a step here; when the tank wouldn’t fill, I removed the cartridge and manually opened the slit; I had thought I had closed it and it was ok to reinsert, but obviously the ensuing overfill was a consequence of doing that poorly.
I’m using the same cartridge now, after reinserting it again, after checking the valve. Still looked that same. Not sure just what I did that wouldn’t let it reseal, but it ain’t no nevermind. All is well now. Running the first print.
Working is working.
There’s some very clever intelligence in the 2. A major improvement!