Every newsroom already declares what it allows, usually in prose.
Signing the declaration converts it into something machines can check without a lawyer in the loop, and something editors can change without waiting for a crawler to be rebuilt.
The failure mode to avoid is silent drift: a policy page that says one thing while the feed says another.
Three files, one policy: the manifest, the delta index, and the revocation registry. When they disagree, clients notice before readers do.