MSC4115: stamp unsigned.membership on a served PDU with the requesting
userβs membership at the time of the event. The MSC permits omitting the
property when calculating it is expensive, so the project restricts it to
encrypted rooms where membership-vs-event ordering matters for key share.
Paginates a roomβs timeline, applying the request filter and (unless
bypass_visibility) the per-user visibility and ignore filters. Powers the
client-server /messages route and its admin bypass twin.
MSC3440 related_by_*: include an event only when another event relates
to it matching the filterβs reverse-relation criteria. A no-op stage when
the filter carries neither field.