Artifacts stop pulling without visible failure

Sometimes, artifacts get stuck in a state of being "pulled" but no network traffic occurs. Buildstream will never finish or stop trying to pull these artifacts. These pulls never hit timeouts or retries. I can even turn off my network connection and buildstream will still present these as being actively pulled for hours, never showing a failure (even though the network is down).

I have hesitated to open this issue for a while because, unfortunately, I have not found clear reproduction steps for this. This has just occasionally happened for months with no clear pattern. Nothing is logged with default logging options.

Start by investigating the artifact-pulling path and how it handles network loss, timeouts, and retries. Reproduce or instrument a pull while disconnecting the network, then verify that the pull eventually reports a failure and that the outcome is visible with default logging.

Written by the indexing model from the issue text.