First message in a DM was not encrypted

[andybalaam]

Steps to reproduce

1. Start new chat
2. Type mxid of other person, click Go
3. Type a message to the other person

Outcome

What did you expect?

I expected all messages in this DM to be encrypted.

What happened instead?

The first message was not encrypted:

Source of that first event:

{
  "content": {
    "body": "Hi, thank you for looking at MSC3757, and sorry I have neglected it!",
    "m.mentions": {},
    "msgtype": "m.text"
  },
  "origin_server_ts": 1727188841453,
  "sender": "@andybalaam:matrix.org",
  "type": "m.room.message",
  "unsigned": {
    "membership": "join",
    "age": 12541,
    "transaction_id": "m1727188841284.81"
  },
  "event_id": "$RX_kUJTWDQL3DVE1fRkx2foUYt73DXpyaMlHRA73TXU",
  "room_id": "!qKSwlzySCzuQreJffe:matrix.org"
}

Later messages in this DM were encrypted as expected.

Operating system

Debian 12.7

Browser information

Firefox 130.0

URL for webapp

https://develop.element.io

Application version

Element version: 787feca-react-a1bdceed3e54-js-f8208b18916d Crypto version: Rust SDK 0.7.2 (7a21514), Vodozemac 0.7.0

Homeserver

matrix.org

Will you send logs?

Yes

[kegsay]

This could be due to the same race condition I outlined in my UTD talk - if we only latch encryption on if we see the m.room.encrpytion state event, then what happens if you try to send a message before the client is notified about that event via /sync?

[BillCarsonFr]

I recently had a similar problem of EW sending in clear but with a local setup, I sent a RS https://github.com/element-hq/element-web-rageshakes/issues/27122
As far as I remember it was not a fresh DM. Maybe not related as it was a local setup running local code. But yet adding here