Nine change-detector tests become four invariants (one per behaviour, two
behaviours per module): every realm-escaping / unknown / mixed-case token is
dropped and an emptied set falls back to the default posture; allowlisted
tokens survive deduped; the rendered frame carries the posture; props cannot
re-open it.
Docs: TS signature, the exact allowlist and the strip list the ruling names
(allow-same-origin, allow-top-navigation*, allow-popups*, allow-modals,
allow-storage-access-by-user-activation), teardown, and the rss-reader
(#115972) migration off its stubbed /preview → openExternal chain.
a48557baff