MSC: https://github.com/matrix-org/matrix-spec-proposals/pull/4284 * [x] Call `/sign` instead of `/check` as a fallback (and persist signatures) * [x] Ensure events (soft) fail rather than pass due to lack of signatures * [x] For 3-6 months, fall back to unstable `/sign` * https://github.com/element-hq/synapse/issues/19502 * [x] Proxy error responses from policy server to client-server API * [x] Support stable event type `m.room.policy` * [x] Fix shallow update when signatures are on the same domain
MSC: matrix-org/matrix-spec-proposals#4284
/signinstead of/checkas a fallback (and persist signatures)/signm.room.policy