I have a mixed update. It took a few weeks for the WSON-8 6x5 test probe to arrive, but it came yesterday. I was able to use it to pull the contents of the flash closest to the EC on the bottom side of the mainboard, and the first 0x80000 bytes exactly match what ECTool pulled in its backup, so that looks good.
The other two flash chips on the bottom have what appears to be other firmware for some other components. Both have very different contents and none of them match the ECTool backup, so I’m just going to leave them alone. If someone wants, I can post the contents of those chips somewhere.
So, feeling confident I have an escape hatch, I reassembled my laptop, and… it wouldn’t charge or boot. It had been disconnected from battery for like 3 weeks. I was pretty careful handling the mainboard, so I’m not sure what the issue could have been.
I saw some suggestions that I should pop out and in the CMOS battery and try trickle charging it. Unfortunately, I cracked the CMOS receptacle, so Framework is luckily replacing the mainboard for me. When I get that replaced I guess I will get new flash backups and then finally try the flashing.