fix: add self user to MLS conversation when joining via invite link [WPB-22305]

[MohamadJaara]

WPB-22305 [Web] Joining MLS conversation by guest link doesn't produce welcome message

when joining a conv via invite link the web app was not sending welcome message to invite self user other clients to the conv

to test the fix you must have user A on web and mobile, and user B does not matter

1. B create a new empty MLS group
2. B create an invite link and send it to A in 1:1
3. A open the link from their web client
4. B send a message in that group

expected:
A should see this message on web and mobile
actual:
A sees the message only on web

to fix it i used codex with GPT-5.5 using this prompt

---

join an MLS conv via invite link is broken for other self clients when joining from this web app
my theory is the app is not doing step 8 from what the android app is doing

Here’s the Android/Kalium flow for “join MLS conversation via invite link”, with the CoreCrypto calls called out.

Flow

1. Public API: JoinConversationViaCodeUseCase
   calls conversationGroupRepository.joinViaInviteCode(code, key, null, password).

2. Backend invite join: ConversationGroupRepository
   calls:

   conversationApi.joinConversation(code, key, uri, password)

   Network side is POST /conversations/join.

3. If backend returns Changed, Kalium emits the local member-join event, reads the conversation protocol, and if it is MLS-capable starts crypto transaction joinViaInviteCode.

4. Inside that transaction, Kalium first joins the MLS group:
   JoinExistingMLSConversationUseCase
   fetches group info:

   GET /conversations/{domain}/{conversationId}/groupinfo

   implemented at ConversationApiV5.

5. Then Kalium calls:

   mlsConversationRepository.joinGroupByExternalCommit(mlsContext, groupId, groupInfo)

   which calls CoreCrypto:

   mlsContext.joinByExternalCommit(groupInfo)

   at MLSConversationRepository.

6. The actual CoreCrypto binding call is:

   context.joinByExternalCommit(
       groupInfo = publicGroupState.toGroupInfo(),
       customConfiguration = CUSTOM_CONFIGURATION_DEFAULT,
       credentialType = DEFAULT or X509,
   )

   at MLSClientImpl.

7. After that succeeds, Kalium reads the local epoch:

   mlsContext.conversationEpoch(groupId)

   and marks the local DB group state as ESTABLISHED.

8. Important second step: after external commit succeeds, invite-link join also calls:

   mlsConversationRepository.addMemberToMLSGroup(
       mlsContext,
       groupId,
       listOf(selfUserId),
       cipherSuite
   )

   See ConversationGroupRepository.

9. addMemberToMLSGroup first commits pending proposals:

   mlsContext.commitPendingProposals(groupId)

   then claims key packages for selfUserId, then calls either:

   mlsContext.addMember(groupId, clientKeyPackageList)

   or, if there are no key packages:

   mlsContext.updateKeyingMaterial(groupId)

   See MLSConversationRepository and MLSConversationRepository.

10. CoreCrypto implementations for those are:

context.commitPendingProposals(groupId.toCrypto())
context.addClientsToConversation(groupId.toCrypto(), keyPackages)
context.updateKeyingMaterial(groupId.toCrypto())

See MLSClientImpl and MLSClientImpl.

Transport detail web may be missing
Kalium does not manually POST every generated MLS commit from the repository. The MLS client is created with an MLSTransporter; CoreCrypto uses that transport to send commit bundles. The transport calls:

mlsMessageApi.sendCommitBundle(...)

which posts:

POST /mls/commit-bundles
Content-Type: message/mls

See MLSTransportProvider and MLSMessageApiV5.

So the short version to send web is:

After POST /conversations/join succeeds for an MLS conversation:
1. Fetch /conversations/{domain}/{conv}/groupinfo.
2. Call CoreCrypto joinByExternalCommit(groupInfo, config, credentialType).
3. Let CoreCrypto/MLS transport send the produced commit bundle to POST /mls/commit-bundles.
4. Read local conversationEpoch and mark local group established.
5. Then add the current user/self clients to the MLS group:
   - commitPendingProposals(groupId)
   - claim self key packages
   - addClientsToConversation(groupId, keyPackages)
     OR updateKeyingMaterial(groupId) if no key packages
6. Those commit-producing calls also need their commit bundles sent via POST /mls/commit-bundles.

[github-actions]

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🧪 Playwright Test Summary

• ✅ Passed: 15
• ❌ Failed: 0
• ⏭ Skipped: 0
• 🔁 Flaky: 0
• 📊 Total: 15
• ⏱ Total Runtime: 111.0s (~ 1 min 51 sec)

[sonarqubecloud]

Quality Gate passed

Issues
4 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud