Yep, my Fraunchpad is borked!
As best as I can determine, I was playing with MSPDebug on Linux with my Fraunchpad and must have, somehow, written into one or more of memory locations 0x17FC to 17FF. Can anyone guess what that does to an MSP430FR5739? It irreversibly disables the JTAG interface and now my board is, well, rather useless. I tried using IAR under Windows but it wouldn't talk to my Fraunchpad either. I really wish that TI had designed this puppy to expected a very specific bit pattern in those memory locations instead of allowing anything other than all zeros or all ones to pop the security fuse.
Oh well, live and learn...
-Rusty-