The cancel-loose-end guards (cancel approval / question / reminder)
inferred manager-level privilege by string-matching the canceller
against the hardcoded `hive_sh4re::MANAGER_AGENT` ("ruth"). That laundered
privilege through a name: a request arrives on the privileged manager
socket, gets stamped with the bootstrap agent's name, and the guards
re-derive privilege from that name. Renaming or replacing the bootstrap
agent would then silently move privilege.
Privilege is a property of the SOCKET the request arrived on (the manager
socket is the trust boundary), so thread an explicit `privileged: bool`
through `dispatch_shared` → `handle_cancel_loose_end` → the three guards:
- `Broker::cancel_reminder_as` and `OperatorQuestions::cancel`: the
`== MANAGER_AGENT` leg becomes `privileged` (owner/asker + operator name
legs unchanged).
- `check_approval_canceller_is_manager(canceller)` →
`check_can_cancel_approval(privileged)` (manager-socket-only); unit tests
updated to assert on the flag.
The manager socket passes `privileged = true`; the agent socket passes
`false`. `MANAGER_AGENT` is still passed as the actor NAME for legitimate
attribution/routing (notifications, schedule ownership, bootstrap
destroy-protection) — those are not privilege checks and are left intact.
Scope is the privilege guards only.
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