I did read both of those – I wouldn’t have made it this far without them 
– but I’m not seeing where I’m diverging from the instructions. I also tried to read through this forum thread: Including shared pde files across projects (though I got a little lost in which things did and did not work) and I think what I have follows the example in https://github.com/GoToLoop/Processing_Jar_Creation
But I’m not in any sense a Java developer so it’s entirely possible I got the “building the .jar” part wrong, since that’s the part that’s glossed over in the Wiki entry. What I did was run, in a directory containing only name.java:
javac -d ./build -classpath /Applications/Processing/Processing.app/Contents/Java/core/library/core.jar:/Applications/Processing/Processing.app/Contents/Java/modes/java/libraries/net/library/net.jar *.java
cd build
jar cvf name.jar *
Do I maybe need other things in that directory when I make the .jar?