Sender key distribution unreliable when running in embedded mode

[hughns]

When running as a widget (embedded mode) within Element X and Element Web, there have been reports of participant sender keys not finding their way to other recipients. This has resulted in those recipients not able to decrypt the media and so shows a grey box instead.

Apparently it is intermittent. This could be in the widget API interface or somewhere else. The keys are distributed via encrypted room events.

Whilst there is discussion about moving key distribution to use to-device messaging instead of encrypted room events for other reasons, it is not known if the root cause of the problem would also affect an alternative implementation

Possible next steps:

• Add tactical logging around key distribution (there is very little at the moment)
• Wait for some rageshakes reports
• Investigate those rageshakes and iterate