Some error messages from "lfs mirror extend" start with "lfs mirror mirror" others start with "error: ". Both should start with "lfs mirror extend: ".

# lfs mirror extend -N -p ddn_ssd f0
lfs mirror mirror: cannot get UNLOCK lease, ext 4: Device or resource busy (16)
error: lfs mirror extend: f0: cannot merge layout: Device or resource busy

The first message should include the file path or at least FID. Paths should be enclosed in single quotes. We should not print two errors for the same message.