same batch are complete. Only objects which were reported
in the output of 'list' with a sha1 may be fetched this way.
+
-Optionally may output a 'lock <file>' line indicating a file under
-GIT_DIR/objects/pack which is keeping a pack until refs can be
-suitably updated.
+Optionally may output a 'lock <file>' line indicating the full path of
+a file under `$GIT_DIR/objects/pack` which is keeping a pack until
+refs can be suitably updated. The path must end with `.keep`. This is
+a mechanism to name a <pack,idx,keep> tuple by giving only the keep
+component. The kept pack will not be deleted by a concurrent repack,
+even though its objects may not be referenced until the fetch completes.
+The `.keep` file will be deleted at the conclusion of the fetch.
+
If option 'check-connectivity' is requested, the helper must output
'connectivity-ok' if the clone is self-contained and connected.