0.8.1: Mac model Get fails on a slow link #366

Split from #84. Known issue in the 0.8.0 release notes.

On a slow link the Mac's Get fails with 'Model content could not be read' after Carrier's 5 s reply deadline.

Done means

• Get completes on a slow link, or stops with a plain reason and Retry resumes it. Test: on a Mac with a throttled link, Get Qwen; it finishes or Retry resumes from the saved bytes.