Comment 1 for bug 1837369

The 'block-devices' interface is meant for things like smartctl and hdparm (or flashing tools) to perform actions on raw disks. It says specifically: "Only allow raw disk devices; not loop, ram, CDROM, generic SCSI, network, tape, raid, etc devices or disk partitions"

So block-devices should not be extended to individual partitions.

hardware-observe is meant to allow lsblk and querying udevadm, have you tried that? /sbin/blockdev is not included in hardware-observe and would need to be added, but you might be able to use stage-packages in the meantime.