The site role
One Named Person Says Go,
and Can Say Stop.
Every job has a person behind it, by name. They clear the job before the machine is armed, choose whose way of working is in the seat, authorize the task and can take authority away at any moment. The unit can do none of those things for itself.
Authority on this line has three parts, and all three are written down: what the machine may do, who authorized it, and when the authorization ends.
Two authorizations stack. Canadian Shield issues the line's authorization as a lease: time-limited, signed, delivered by wire or at the dock, never by radio, and withdrawable. Your named person authorizes each task inside that lease. Either one ending has the same result: a safe stop at the next safe point, then the minimum-risk condition for that task. The unit stays installed and will not run until it is re-authorized, and the host machine is never touched.
Before every session the unit asks one thing first: whose way of working is in the seat today. The basic set it came with, the way your own operator taught it, or a specialist hired by name. There is no default and no last-used. Somebody chooses, and the record carries the name of whoever did.
A key is a human authority token, and key rotation is excluded from the unit's actuator set. A person starts the machine on Responder and civil work, every session. On Defender the machine may be started on a remote command from the stand-off station, over the tether, on ground closed to everyone the job does not need and with nobody at the machine; the authorization, the wired stop and the manual release are unchanged by it.