`policy::render()` became `render(hive)` when a hive gained read on its own
entry, so two places now describe a document that no longer exists: this
module's header said it "is the same for every hive and depends on nothing",
and the security doc said the grant reaches the agent-credential prefix and
nothing else.
The module header is the load-bearing one. It sits above `write_policy_for`
and says, to anyone about to touch that function, that the render is
hive-independent — which is an invitation to hoist it to a shared constant
and hand every hive the stanza naming one of them.
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