Happier conclusion to this: I now use Google Drive, having uninstalled TeamViewer everywhere.

Each morning I can upload the night's images from the observatory PC to (free) Google Drive; simultaneously Google Backup and Sync on my home office PC download them automatically. Then when I drag the image folder to my work drive, the images disappear from Google Drive but not from the observatory PC. Nicer and much faster than I expected.

But I don't sync the observatory PC to Google Drive, for pretty good reasons: (1) upload times are negligible, (2) while running ACP etc I want the absolute fewest possible other processes running, and (3) when I move the images out of the home office Google Drive folder, google Sync would delete them off my *observatory* PC by relayed sync (eek).

(Yes it's annoying to give Google access to more data, but if they can divine purchase intent from FITS files, Civilization is canceled anyway...)