Relay added on Android 2.56 is not synchronized to Desktop 2.53

[h31]

• Operating System (Linux/Mac/Windows/iOS/Android): Android 15 and macOS 26
• Core Version:
  • Android: 2.56.0
  • Desktop: 2.53.0
• Client Version: Latest stable versions
  • Delta Chat Android 2.56.0-gplay
  • Delta Chat Desktop 2.53.0

Expected behavior

I added another relay to an existing profile on Android. I expected the new
relay to be synchronized to macOS using the same profile.

Actual behavior

The relay was added successfully on Android, and the client there connects to
it. However, the relay does not appear on macOS.

MacOS client receives a synchronization message, but the log contains:

executing 1 sync item(s)
Ignored unknown sync item: {"Transports":{...}}

I noticed that OAuth-related fields were recently removed in this commit: 5c1e695

Perhaps this is related, since the synchronization message was sent by core
2.56.0 and received by core 2.53.0. This is only a guess based on comparing the
versions and looking at the log.

Steps to reproduce the problem

1. Use the same profile on Android 2.56.0 and Desktop 2.53.0.
2. Add another relay on Android.
3. Wait for the Desktop client to receive the synchronization message.
4. Open the relay list on Desktop.
5. The new relay is not present.
6. The Desktop log shows Ignored unknown sync item for a Transports item.

Screenshots

Logs

I am not attaching the complete log because the logged Transports payload
contains relay credentials.

[nicodh]

The same happens the other way round: Adding a second device from desktop 2.56.0 to Android < 2.56.0 fails with:

07-25 11:09:16.430  8212  8274 🔴 DeltaChat: [accId=97] Failed to start IO: missing field `oauth2` at line 1 column 938
07-25 11:09:16.430  8212  8274 🔴 DeltaChat: Failed to start IO: missing field `oauth2` at line 1 column 938