After channels.leaveChannel, a client that polls channels.getFullChannel kept
receiving a projection that still showed it as an active member (left=false)
until the per-(viewer,channel) RPC projection cache and the store-level member
cache lapsed on their own or the async read-model NOTIFY landed. The client
therefore kept an open compose box while every send was already rejected with
CHANNEL_PRIVATE - most visible on public forum supergroups, where getFullChannel
keeps succeeding via the preview path instead of tearing the chat down.
Every other membership-mutating path already busts these caches synchronously;
join/leave/invite/request-approval did not. Add:
- store: invalidateChannelMembershipCaches (row + member + dialog caches),
called post-commit from JoinChannel, LeaveChannel, ImportInvite,
InviteToChannel.
- rpc: invalidateChannelMembershipProjection (channelFullProjectionCache pair),
called from the join/leave/invite/hide-requests handlers for every user whose
membership changed.
