How to handle event edits when excluding insecure devices

[richvdh]

Link to problem area:

matrix-org/matrix-spec-proposals#4153

Issue

MSC4153 requires that

Encrypted messages from non-cross-signed devices SHOULD be ignored

Now consider the following situation

• Alice sends an event from her cross-signed device, device A
• Alice sends an edit of that event from her non-cross-signed device, device B

What should Bob's client show? It seems like he should ignore the event edit (treating it the same way as other invalid edits), but this could do with being clarified, and we should make sure that the implementations in EW and EX do so.

[richvdh]

Related: #2294