Can't start pool

(venv) root@chia-pool:~/pool-reference# CHIA_ROOT="/root/.chia/mainnet/" ./venv/bin/python -m pool
Traceback (most recent call last):
File "/usr/lib/python3.10/runpy.py", line 196, in _run_module_as_main
return _run_code(code, main_globals, None,
File "/usr/lib/python3.10/runpy.py", line 86, in _run_code
exec(code, run_globals)
File "/root/pool-reference/pool/main.py", line 1, in
from pool.pool_server import main
File "/root/pool-reference/pool/pool_server.py", line 35, in
from .pool import Pool
File "/root/pool-reference/pool/pool.py", line 50, in
from .singleton import create_absorb_transaction, get_singleton_state, get_coin_spend, get_farmed_height
File "/root/pool-reference/pool/singleton.py", line 20, in
from chia.types.blockchain_format.program import Program, SerializedProgram
ImportError: cannot import name 'SerializedProgram' from 'chia.types.blockchain_format.program' (/root/pool-reference/venv/lib/python3.10/site-packages/chia/types/blockchain_format/program.py)

Start by comparing the import in pool/singleton.py with the installed chia.types.blockchain_format.program module shown in the traceback. Then run the documented pool startup command and verify that the module loads without the ImportError; the issue does not identify a target chia version or intended compatibility change.