A forwarded keyed managed command (registry browse, key-value, forks). Unlike
ForwardedQuery, several op kinds share one path, so the frame carries
command_code and the backend dispatches on it. payload is the opaque
CBOR request the SDK sent.
A forwarded managed query. Carries the authenticated identity the SDK cannot
set itself, plus the opaque request the SDK sent. CBOR-encoded, named fields.