No CUPS server setup can be considered complete without sending a print job to the wrong printer:
Which wouldn’t be quite so bad if the printer weren’t ever so much faster than I am:
It turns out an ordinary clothes iron can flatten those pages. Set it to “silk”, spread packing paper on the ironing board to intercept the toner, iron a few millimeters of pages at a time, and feed them back into the printer.
Back in the day, laser-specific printer paper came with a grain arranged so it wouldn’t curl when you fed it into the printer with the proper side up. Those days are gone; I’ve tried both ways and they both curl.
Protip: When CUPS thinks it’s done with the job and the Web interface shows nothing’s going on, it’s handed the job to the server’s printing subsystem, which continues spooling data to the printer. Choking off the bitstream requires one command-line invocation on the server connected to the printer:
A paper jam gives you enough time to figure all that out.