Steps to reproduce

1. Have a message in a room with explicit mentions (m.mentions in its content)
2. Forward the message to another room

Outcome

What did you expect?

The message's m.mentions should be stripped from the forwarded message (as m.relates_to already appears to be, cf. matrix-org/matrix-react-sdk#7929).

What happened instead?

The message's m.mentions object is not stripped, and is included in the the forwarded message.

This can leak information in a sneaky manner (i.e. not directly observable without noting the message source).

Operating system

No response

Browser information

No response

URL for webapp

staging.element.io

Application version

Element version: 1.12.0

Homeserver

No response

Will you send logs?

No