Haha that’s brilliant! I have a similar script for Conda, where it tries to install R packages by first looking in bioconductor and then trying the rejects through conda-forge, and then the rejects from that are compiled from source or just outright rejected.
I would have thought you would have needed a (while :; do echo; done) | pdflatex or a yes “end” | pdflatex, i.e. something that repeatedly generates output. It’s actually quite elegant that pdflatex checks if stdin is already EOF