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Redeem an enrollment token, registering this machine as the bot's device. Registering the public key and consuming the token are atomic: the token is spent by a conditional UPDATE that exactly one concurrent caller can win, and the device row is written in the same transaction, so a token is never consumed without producing the device it paid for. No session, assertion or SVID is issued here. The device credential buys only the right to *ask* for one, on every future connection, against a registry that can deny it immediately. *** THERE IS EXACTLY ONE WAY TO LEAVE HERE WITHOUT A DEVICE ROW, AND IT IS AN ERROR. *** A 2xx from this endpoint means the registry holds a live, active device for the caller — either written by this call (``201``, ``newly_enrolled``) or read back within it (``200``, the machine already being that device and offering its key). The caller may therefore treat "this call succeeded" as "a device exists server-side", which is the property an installer needs and the one it cannot establish for itself.