- compare-dest skips an exact basis match (leaving a sparse destination) and
still transfers files the basis cannot satisfy; a content mismatch forces a
normal transfer.
- copy-dest materializes the unchanged file as a real local copy (distinct
inode) and transfers content mismatches.
- link-dest hard-links (asserted same inode/nlink to the DIR file) and falls
back to a normal transfer on content mismatch.
- a missing basis dir is a clean full-transfer no-op for all three flags.
- link-dest works through -m multithreading and --delay-updates (staged and
published as a real link, staging cleaned up).
- --delete removes genuine extras while leaving the basis dir untouched.