[[w:Birthday]]
brew install imessage-ruby
It feels blasphemous to say so, but I believe I may have actually outdone the Original Masterpiece, Bee Movie Spam...
This shortcut uses a Run Shell Script action commanding iMessage-ruby on macOS to send the entirety of the Spy Kids 3 screenplay (or at least... I think it's the actual screenplay - not actually sure, nor does it matter,) line-by-line to a specified phone number via Messages.
The command itself:
imessage --text "Repeat Item" --contacts "Provided Input"
By my count, the screenplay text totals 6937 words in 1559 lines, which means 1559 messages total. I've tested it once all the way through just to confirm the cycle will complete, but didn't think to set a timer. It was more than 10 minutes, less than 30, I'd say.
I left my own phone number - +15738234380 - in the Default Number field of the Ask for Input action very much on purpose - I promise it'll make my day if you use me as a test subject.