MAX10: JTAG sharing not working -- how to erase fw-image?

I got into the same problem - programmed an image which didn't define the JTAG pins in my design, so that instead of becoming shared under the control of JTAGEN they became undedicated inputs.

As described in the other link, problem solved by defining three inputs and an output in the HDL and assigning them to the TDI/TDO/TMS/TCK pins.

I rescued my 'bricked' prototypes by soldering a wire onto my nSTATUS and CONF_DONE pins (probably just one of them would have been enough), and holding it to GND while powering up the board. The JTAG will then operate to program the internal memory (or simply erase), and after that things are back to normal and I could remove my wire.

I didn't find a way to soft-configure the device in that state - the JTAG could load the RAM image but holding down the nSTATUS all the way through prevented it from configuring after the download, and letting go of it too soon seemed to start an internal-configure with the bogus image.

Hopefully the OP solved is problem before now, but maybe this will help someone finding this page on a search like I did.