FrameworkHacksPkg VS debugprobe

No problem, let me just use ECTool to reflash the backup. Uh oh, the first thing ECTool does is say "press any key to abort". Due to my keys repeating, it kept aborting! Finally after some panicking, I figured out I could press Shift after hitting Enter, and it wouldn't count for its "press any key" logic. With that, I was able to reflash a backup. As a side note, I have a fork of ECTool that adds an option to avoid the "press any key to abort" behavior. I'll see about getting this feature into ECTool proper.

use the JECDB header to connect a SWD probe like a Picoprobe and debug the firmware

Can Raspberry Pi Pico replace J-Link? I saw PicoProbe project, installed and wired for it, but pyocd stucks with "Waiting for a debug probe to be connected..." and nRF Connect Programmer fails with error "Unsupported device. The detected device could not be recognized as neither JLink device nor Nordic USB device."

Even once you've got that handled, though, I'm not sure the JLink will be able to connect. The RP2040 uses a somewhat uncommon variant on SWD to communicate with its two cores; not all debug probes support this. If you can't get the JLink to work and you have a spare Pi Pico around, you can use the Picoprobe firmware to turn the extra Pi into a DAPlink-compatible debug probe.

That's cool, but does it do anything you can't already do with just another Pico running picoprobe? (like this)

I need to boot rp2040 from ram (no flash), which I have tested with the picotool (with USB) and picoprobe (with swd+gdb load) and I can boot from ram and flashing a LED.

Yes -- the Picoprobe firmware is what you're after.

And here's the repo for the picoprobe software: https://github.com/raspberrypi/picoprobe