Pylance & Pylint report “could not be resolved” / “no-member” for a valid PyPI package in VSCode virtual environment

What configuration changes are needed in VSCode (or in my project layout) to make Pylance and Pylint recognize the installed cowsay package and its members? Is there a best practice for structuring local packages alongside third-party libraries so that both analysis engines pick them up correctly?

I’ve created a Python 3 virtual environment in VSCode (using python -m venv venv at the project root), installed the cowsay library via pip, and selected the interpreter from venv. However, in my source file I see:

Import "cowsay" could not be resolved  PylancereportMissingImports
Module 'cowsay' has no 'cow' member  PylintE1101:no-member

Code:

import cowsay
import sys

if len(sys.argv) == 2:
    cowsay.cow("Hello there, " + sys.argv[1])

This happens even though running the script with:

./venv/bin/python3.13 packages/say.py carl

prints the correct output:

./venv/bin/python3.13 packages/say.py carl
  _________________
| Hello there, carl |
  =================
                 \
                  \
                    ^__^
                    (oo)\_______
                    (__)\       )\/\
                        ||----w |
                        ||     ||

Project structure:

project-root/
├── packages/
│   └── say.py
├── venv/                ← virtual environment

Confirming VSCode is using the venv/bin/python interrupter