OK, found ( a night sleep helps).
I successfully recovered the storage, apparently:
mcon@cinderella:~$ sudo lxd recover
This LXD server currently has the following storage pools:
Would you like to recover another storage pool? (yes/no) [default=no]: yes
Name of the storage pool: default
Name of the storage backend (lvm, zfs, btrfs, dir): zfs
Source of the storage pool (block device, volume group, dataset, path, ... as applicable): homez/lxd
Additional storage pool configuration property (KEY=VALUE, empty when done): zfs.pool_name=homez/lxd
Additional storage pool configuration property (KEY=VALUE, empty when done):
Would you like to recover another storage pool? (yes/no) [default=no]:
The recovery process will be scanning the following storage pools:
- NEW: "default" (backend="zfs", source="homez/lxd")
Would you like to continue with scanning for lost volumes? (yes/no) [default=yes]:
Scanning for unknown volumes...
The following unknown volumes have been found:
- Container "nrf-builder" on pool "default" in project "default" (includes 0 snapshots)
- Container "nrf-devel" on pool "default" in project "default" (includes 0 snapshots)
- Container "seeme-builder" on pool "default" in project "default" (includes 0 snapshots)
- Container "yocto-builder" on pool "default" in project "default" (includes 0 snapshots)
- Container "lxdMosaic" on pool "default" in project "default" (includes 0 snapshots)
You are currently missing the following:
- Network "lxdbr0" in project "default"
Please create those missing entries and then hit ENTER:
The following unknown volumes have been found:
- Container "lxdMosaic" on pool "default" in project "default" (includes 0 snapshots)
- Container "nrf-builder" on pool "default" in project "default" (includes 0 snapshots)
- Container "nrf-devel" on pool "default" in project "default" (includes 0 snapshots)
- Container "seeme-builder" on pool "default" in project "default" (includes 0 snapshots)
- Container "yocto-builder" on pool "default" in project "default" (includes 0 snapshots)
Would you like those to be recovered? (yes/no) [default=no]: yes
Starting recovery...
mcon@cinderella:~$ lxc list
+---------------+---------+------+------+-----------+-----------+
| NAME | STATE | IPV4 | IPV6 | TYPE | SNAPSHOTS |
+---------------+---------+------+------+-----------+-----------+
| lxdMosaic | STOPPED | | | CONTAINER | 0 |
+---------------+---------+------+------+-----------+-----------+
| nrf-builder | STOPPED | | | CONTAINER | 0 |
+---------------+---------+------+------+-----------+-----------+
| nrf-devel | STOPPED | | | CONTAINER | 0 |
+---------------+---------+------+------+-----------+-----------+
| seeme-builder | STOPPED | | | CONTAINER | 0 |
+---------------+---------+------+------+-----------+-----------+
| yocto-builder | STOPPED | | | CONTAINER | 0 |
+---------------+---------+------+------+-----------+-----------+
… but something is still amiss:
mcon@cinderella:~$ lxc delete lxdMosaic
mcon@cinderella:~$ lxc launch ubuntu: lxdMosaic
Creating lxdMosaic
Error: Failed instance creation: Failed creating instance record: Failed initialising instance: Invalid devices: Failed detecting root disk device: No root device could be found
I seem to have found root cause:
mcon@cinderella:~$ lxd init --dump
config: {}
networks:
- config:
ipv4.address: 10.194.203.1/24
ipv4.nat: "true"
ipv6.address: none
description: ""
name: lxdbr0
type: bridge
project: default
storage_pools:
- config:
source: homez/lxd
volatile.initial_source: homez/lxd
zfs.pool_name: homez/lxd
description: ""
name: default
driver: zfs
profiles:
- config: {}
description: Default LXD profile
devices: {}
name: default
projects:
- config:
features.images: "true"
features.networks: "true"
features.profiles: "true"
features.storage.volumes: "true"
description: Default LXD project
name: default
Apparently I am missing some devices: in my default profile; I expected something like:
...
profiles:
- config: {}
description: Default LXD profile
devices:
eth0:
name: eth0
nictype: bridged
parent: lxdbr0
type: nic
root:
path: /
pool: default
type: disk
name: default
...
Should I retry initialization?
I wouldn’t like to mess further with a half-crippled system without proper knowledge 
Probably editing default profile should be enough, but I’m unsure 
.
SUCCESS!!
lxc profile edit default did the trick.
Many thanks to @tomp: I will mark his answer as solution (and leave all this for future reference).