Auto-detect whether session is interactive, and accordingly whether to perform background fetching

See here:
https://stackoverflow.com/questions/2356399/tell-if-python-is-in-interactive-mode

No file, test, or entry point is named. Start by tracing where background fetching is initiated and how the Python package detects its execution context, then use the linked Stack Overflow discussion as background. Done means interactive sessions and non-interactive sessions select the intended fetching behavior, with tests covering both cases.

Written by the indexing model from the issue text.