Error codes: 1000-1001: device errors (not found, permission) 2000-2002: profile errors (unsupported, not found, parse) 3000-3003: unlock errors (failed, signature, not unlocked, not calibrated) 4000-4001: SCSI errors (command failed, timeout) 5000: I/O errors All errors carry structured data (vendor_id, opcode, etc). Applications format their own user-facing messages. Library returns code + data, never English text.