[Bug]: user-packages take precedence over pgai dependencies

[JamesGuthrie]

What happened?

In the pgai function initialization code, we remove site packages from sys.path to prevent system-packages from taking precedence over our packages.

user packages are also affected, and take precedence over our packages.

Concretely in a user's installation, we saw the following configuration:

Ollama install locations:

/home/<user>/.local/lib/python3.13/site-packages/ollama-0.2.1.dist-info
/home/<user>/.local/lib/python3.12/site-packages/ollama-0.2.1.dist-info
/usr/local/lib/pgai/0.7.0/ollama-0.4.5.dist-info
/usr/local/lib/pgai/0.6.0/ollama-0.2.1.dist-info
/usr/local/lib/pgai/0.5.0/ollama-0.2.1.dist-info
/usr/local/lib/pgai/0.4.1/ollama-0.2.1.dist-info
/usr/local/lib/pgai/0.4.0/ollama-0.2.1.dist-info
/usr/local/lib/pgai/0.8.0/ollama-0.4.5.dist-info

sys.path: [
  '/usr/local/lib/python312.zip',
  '/usr/local/lib/python3.12',
  '/usr/local/lib/python3.12/lib-dynload',
  '/home/<user>/.local/lib/python3.12/site-packages',
  '/usr/local/lib/python3.12/site-packages'
]
sysconfig.get_paths: {
  'stdlib': '/usr/local/lib/python3.12',
  'platstdlib': '/usr/local/lib/python3.12',
  'purelib': '/usr/local/lib/python3.12/site-packages',
  'platlib': '/usr/local/lib/python3.12/site-packages',
  'include': '/usr/local/include/python3.12',
  'platinclude': '/usr/local/include/python3.12',
  'scripts': '/usr/local/bin',
  'data': '/usr/local'
}

pgai extension affected

0.8.0

pgai library affected

PostgreSQL version used

17

What operating system did you use?

Ubuntu

What installation method did you use?

Source

What platform did you run on?

Not applicable

Relevant log output and stack trace

How can we reproduce the bug?

See above

Are you going to work on the bugfix?

None