The sigstore package was updated to v4.0.0 a few days ago and does not pull the sigstore_protobuf_spec in anymore, which we are missing now and this leads to these kind of backtraces:
$ model_signing
Traceback (most recent call last):
File "/home/stefanb/.local/bin/model_signing", line 5, in <module>
from model_signing._cli import main
File "/home/stefanb/.local/lib/python3.13/site-packages/model_signing/__init__.py", line 124, in <module>
from model_signing import signing
File "/home/stefanb/.local/lib/python3.13/site-packages/model_signing/signing.py", line 51, in <module>
from model_signing._signing import sign_certificate as certificate
File "/home/stefanb/.local/lib/python3.13/site-packages/model_signing/_signing/sign_certificate.py", line 29, in <module>
from sigstore_protobuf_specs.dev.sigstore.bundle import v1 as bundle_pb
ModuleNotFoundError: No module named 'sigstore_protobuf_specs'