sequenceDiagram
  participant M as N existing<br>members
  participant A as Alice
  participant B as Bob
  participant C as Existing<br>contact

  note over A, B: 1. send and accept group invitation
  A ->> B: x.grp.inv<br>invite Bob to group<br>(via contact connection)
  B ->> A: x.grp.acpt<br>accept invitation<br>(via member connection)<br>establish group member connection

  note over M, B: 2. introduce new member Bob to all existing members
  A ->> M: x.grp.mem.new<br>"announce" Bob<br>to existing members<br>(via member connections)
  loop batched
    A ->> B: x.grp.mem.intro * N<br>"introduce" members and<br>their chat protocol versions<br>(via member connection)
    note over B: prepare group member connections
    opt chat protocol compatible version < 2
      note over B: prepare direct connections
    end
    B ->> A: x.grp.mem.inv * N<br>"invitations" to connect<br>for all members<br>(via member connection)
  end
  A ->> M: x.grp.mem.fwd<br>forward "invitations" and<br>Bob's chat protocol version<br>to all members<br>(via member connections)

  note over M, B: 3. establish direct and group member connections
  M ->> B: establish group member connection

  opt chat protocol compatible version < 2
    M ->> B: establish direct connection
    note over M, C: 4. deduplicate new contact
    B ->> M: x.info.probe<br>"probe" is sent to all new members
    B ->> C: x.info.probe.check<br>"probe" hash,<br>in case contact and<br>member profiles match
    C ->> B: x.info.probe.ok<br> original "probe",<br> in case contact and member<br>are the same user
    note over B: merge existing and new contacts if received and sent probe hashes match
  end
