Terminal-IDE / wifi routing issues
After some discussions on the (new, and not yet archived) Terminal-IDE community email list, I learned that the configuration should be working correctly!

A bit frustrated, I kept trying and then noticed something that I suppose should not have surprise me: I set one computer screen to 'pinging' the Android device, with ZERO reply for a long time, and forgot about it. Then, I later noticed the pings were getting through and there were zillions of them scrolling past.

From this, and a bit more investigation, I found that the stability of a WiFi connection on my Android device isn't very stable, especially as compared with my laptop. 

In short, "be patient, ping the heck out of it while moving the device to find a good signal path, and it should eventually work."