I thought about it some more, and just to be sure the Eshell bits don't 
regress at some point in the future, I added some new unit tests in 
test/lisp/eshell/esh-proc-tests.el to make sure that Eshell sets the 
`:connection-type' properly. (They're pretty similar to the tests in 
test/src/process-tests.el, really.)