A SEND KEY / REPORT KEY step in the bus-auth handshake mapped every
SCSI error to a cert/key-specific code (AacsCertRejected, AacsCertRead,
AacsKeyRead, AacsKeyRejected, etc.) via map_err(|_| ...). That discarded
the underlying SCSI error, so a transport-layer wedge (bridge crash / USB
disconnect) mid-handshake was reported as 'drive rejected your host cert',
sending operators down a keydb/host-cert dead end for what is really a
replug/power-cycle situation.
Add a handshake_err() helper that keeps the original error when it is a
transport failure (is_scsi_transport_failure) and only substitutes the
handshake-specific code for genuine SCSI rejections. Apply it at every
SEND KEY / REPORT KEY / REPORT DISC STRUCTURE step in both the AACS 1.0
and AACS 2.0 paths. Add a regression test covering both branches.