But wait! ;-).
I think you need NRST on that STLINK header too. Which signals did you hook up when you did your snapped-off-STLINK programming experiment a while back?
We run 8 signals to our programming header:
VCC, GND, NRST, SWCLK, SWD, SWDIO, STLINK_RX, STLINK_TX
I think VCC is so the programmer knows what voltage the target is running at. SWD I don’t use but I think it permits trace/debug stuff.
Here you go… you had five wires hooked up: https://community.openenergymonitor.org/t/stm32-hardware-development/7135/20?u=dbc