No, the disk has not shown that it is disabled. I tried running xfs repair again and to my surprise I think it worked. I restarted the array and Disk1 is now accessible, and I can see the files.
I tried running a parity check (non-correcting), and it went very slowly (~300kbps), so I canceled it. Running a smart test on Disk 1 also yielded an error message (something about being interrupted by host), so I set the disk spindown to never and am in the process of running the extended test again.
I've also tried switching the SATA data/power cables around (after a clean shutdown) to see if that would improve anything.
unraidserver-diagnostics-20240126-1654.zip