How to resume OS X apps that have been suspended by the system
More googling revealed that the process management window I am looking for is the "Force Quit Applications" dialog, and that it can be easily accessed from the Apple () menu or with the keyboard shortcut Command Option Escape.  In normal use, this only has a Force Quit button, but it should also have a Resume button if the system suspends any of my processes again (although I can't directly test this at the moment).