ZFS - gptzfsboot really doesn't work as expected. What am I missing?

From: Frank Leonhardt <freebsd-doc_at_fjl.co.uk>
Date: Tue, 04 Mar 2025 13:07:55 UTC
I'm pushing the boundaries of ZFS and have got into a position where the 
system is trying to boot from a drive that's in the middle of a 
resilver. I can cure this by shuffling the drives around so it picks a 
different one. However, if I don't I get a boot prompt:

----------------

BIOS drive C: is disk0
BIOS drive D: is disk1
BIOS drive E: is disk2

<snip>

Can't find boot/zfsloader

Can't find /boot/loader

Can't find /boot/kernel/kernel

FreeBSD/x86 boot
Default: disk-1:/boot/kernel/kernel
boot:

Can't find /boot/kernel/kernel

FreeBSD/x86 boot
Default: disk-1:/boot/kernel/kernel
boot:


----------------


There is NOTHING I can type to get out of this. I assume 
zfs:zroot/ROOT/current:/boot/zfsloader would be appropriate but it 
doesn't say this when I go back and RTFM. It defaults to trying to load 
disk-1:/boot/kernel/kernel, which is bonkers. I'm seriously wondering if 
the installer has dropped the wrong code there.

The FM says of gptzfsboot:

---

Normally    gptzfsboot will    boot in    fully automatic mode.    
However,  like
        boot(8),    it is possible to interrupt the    automatic boot 
process and in-
        teract  with  gptzfsboot     through a prompt.  gptzfsboot 
accepts all the
        options that boot(8) supports.

---

In my experience today, it accepts NONE of the options that boot 
supports! I think I ought to be able to type a '?' and get a directory 
and so on.

Does anyone have an explanation? Is there some proper documentation for 
this or am I going to have to reverse-engineer the source?

Thanks, Frank.