on a separate note - neither of the two Oaks I've tried this on, no longer work properly. The file did upload to SPIFFS, and I can read it from SPIFFS. On the downside, neither of these Oaks now flash properly. What actually happens is inconsistent. For example, using the BLINK sketch, when not in Config Mode, flashing message does not appear after "sending file", i.e.
Sending file to cloud, to flash Unnamed Device (Device ID: d957040015acac56745f580c)
There's no "Flashing ...." but eventually I do get an
Error : An error occurred while flashing the device:
Sometimes I do get the "Flashing.........." but the Oak light does not flash and it eventually times out. Reboot confirms flash did not work.
Only by shorting pin 1 to ground to enter Config Mode can I get it to flash. Then it sometimes flashes, sometimes stops flashing before the upload is complete. Even when the flash completes, it may reboot into Config Mode (nothing on pin 1), or into a do-nothing mode, or it may rarely do what the sketch intended (i.e. blink, or play a tone, or whatever), or it may revert to what the last sketch was, pre-flash.
Until I can figure this one out (or someone else does) I have to consider the possibility that either SPIFFS has borked my MCUs, or that my implementation of it has. So - beware. And if anyone figures this one out, please let us know.