Thanks for the reply! I thought I had done the search you suggested, but it got me trying different search terms, specifically the M3_wakeupSS_0" term. This lead to articles saying how I had to bypass the M3 processor in the target configuration, which moved me on to the next error, but it's progress. It's now clear that the StaterWare examples are not remotely ready to play. I have more trial-and-error ahead of me.
My new error is:
CortxA8: File Loader: Data verification failed at address 0x80000000 Please verify target memory and memory map.
CortxA8: Unable to terminate memory download: NULL buffer pointer at 0x3a9f
CortxA8: GEL: File: C:\ti\AM335X_StarterWare_02_00_01_01\binary\armv7a\cgt_ccs\am335x\beaglebone\gpio\Debug\gpioLEDBlink.out: a data verification error occurred, file load failed.
But thanks for helping me move forward! I'll mark this question answered, since it's specific to the "held in reset" error.