Message keys withheld due to "Never send encrypted messages to unverified sessions from this session" are not shown as such

[kegsay]

Element-Web, Android and iOS all have the ability to enable a security flag which says something like:

Never send encrypted messages to unverified sessions from this session

This can cause UTDs if the recipient has not been verified yet. We should really be displaying warning banners if there are unverified devices in the room when you are typing a message, to warn the sender that this message will be undecryptable for some devices/users.

This appears at the protocol level as a "withheld" to-device message - https://spec.matrix.org/latest/client-server-api/#reporting-that-decryption-keys-are-withheld with the code of m.unverified.

• Element-R: withheld messages are no longer shown as such element-web#27653
• Withheld messages are not shown as such element-ios#7825
• Element X

[BillCarsonFr]

This is actually a expected UTD, we should probably report it as such.
Check that we properly display the withheld code to the user, if not it's bug.

[richvdh]

Can confirm this doesn't work correctly in Web: element-hq/element-web#27653

[richvdh]

element-hq/element-web#27653 is now fixed, and EW now shows "The sender has blocked you from receiving this message because your device is unverified".

However, this remains a problem in Element iOS (element-hq/element-ios#7825) and Element X.