Group Message History — IQ stanza format for adding participants with history sharing?

[dahux-net]

WhatsApp launched Group Message History in February 2026: when adding a participant, admins can share recent messages with the new member.

I'm trying to implement this in my whatsmeow-based bridge. I've found the relevant protobufs in whatsmeow already:

• supportGroupHistory capability flag in WACompanionReg.proto
• waGroupHistory/WAWebProtobufsGroupHistory.proto with GroupHistory message bundle
• isGroupHistoryMessage and GroupHistoryBundleInfo in WAWebProtobufsWeb.proto

But I can't find the trigger mechanism, the correct IQ stanza format for requesting history when adding participants.

I've tried adding attributes to the IQ node:

<iq xmlns="w:g2" type="set" to="group@g.us">
   <add share_history="true" history_length="25">
      <participant jid="..."/>
   </add>
</iq>

This hangs, and WhatsApp server never responds.

Also tried history as a child node:

<add>
  <participant jid="..."/>
  <history length="25"/>
</add>

Same result.

Is the history sharing triggered via a different mechanism entirely (separate IQ, protobuf payload, group-level setting)? What's the correct stanza format?

[dahux-net]

Bumping this with a small update: whatsmeow is now at v0.0.0-20260529101937 and the Group Message History trigger still isn't in the high-level API — UpdateGroupParticipants only accepts add/remove/promote/demote.

To summarize what I've confirmed so far:

• The protobufs are all present (supportGroupHistory capability flag, waGroupHistory bundle, isGroupHistoryMessage / GroupHistoryBundleInfo)
• Adding share_history="true" / history_length="25" attributes to the IQ node (xmlns w:g2, type set) hangs — no response from server
• Adding a child node hangs the same way
• Regular participant add works fine (same IQ without the extra attributes)

Is the history-sharing trigger a separate IQ/mechanism entirely (e.g. a dedicated stanza or protobuf payload sent after the add), or does the official client set a group-level attribute first? If anyone has captured the stanza the official app sends when adding a member with "Share 25 messages," that's exactly what I need.

Related: discussion #502 (chat history), issue #654 (requesting historical messages) — neither covers this.