I am trying to get use the uv bootstrapping with a custom extension and get the following error:

Bootstrap failed while executing: set -e;
            uv sync --frozen --no-install-package metaflow --no-install-package _pythonpath_0;

It looks like it thinks that our extensions package name is

_pythonpath_0

I ran a simple flow with

METAFLOW_DEBUG_EXT=1 METAFLOW_ENVIRONMENT=uv ...

and got the following:

metaflow_extensions: 'metaflow_extensions' distributions order is []
metaflow_extensions: Non installed packages present at {'/path/to/.venv/lib/python3.11/site-packages/metaflow_extensions'}
metaflow_extensions: Walking path /path/to/.venv/lib/python3.11/site-packages/metaflow_extensions (package name _pythonpath_0)
metaflow_extensions:     Extends 'config' with config 'metaflow_extensions.deliveryhero.config.mfextinit_deliveryhero'
metaflow_extensions:     Extends 'plugins' with config 'metaflow_extensions.deliveryhero.plugins.mfextinit_deliveryhero'
metaflow_extensions:     Extends 'plugins.cards' with config 'None'

I think you probably want to install custom extensions that are in a pyproject.toml / requirements.txt rather than installing them with the metaflow package.