Thank you Gardin. You would not believe the man-weeks we have wasted on the how fragile the IDE system. It doesn't seem to matter which IDE we have used: Eclipse, Espressif-IDE, PlatformIO, VSCode - the system will work fine for a few days and then simply stop communicating with the debugger. It has got to the point where we would run [idf.py flash] from the command line, and then start the debugger to attach to a running system. This worked OK up until the last few hours (which I've wasted trying various power cycles, resets, rebuilds etc.) In 30+ years of development I have never used such a terrible set of tools. Are we not seeing more reports of this because very few use the IDF - and use Arduino instead?
Yet for all the wasted days/weeks the fix was running openocd from the command line - sweet! In my case I was using an ESP32S3 with the internal USB/JTAG interface, so for anyone else having the same issues the command (having done all the regular stuff to set up the environment variables:
was
openocd -f board/esp32s3-builtin.cfg
Now this is of course a workaround to the current fragility, so if anyone has a much better fix, which perhaps includes reflashing the code instead of having to use the command line tools, that would be very much welcomed! (If I fix it myself I'll post the solution here - I can't be only us with the issues.)