Add extensible-event fallback/text description to `protocol::OfferContent`

[ShadowJonathan]

Taking a look at the code, and thinking how someone would encounter this in the wild, one suggestion i have to add a little bit of grease is to add an extensible-event "content" / "text" to protocol::OfferContent, so that anyone seeing that message via an IM client knows that someone else sent a file.

Something like "[MXRXTX download offer, use mxrxtx download to download, see eras/mxrxtx for more information]" would work to guide people along.

[eras]

That's a good idea and actually on the todo list!

However, after playing a bit with Element's devtools/add event to timeline I was not able to get Element to render any such event, even after enabling rendering of MSC1767 events :/.

I was considering of non-standard embedding of the data inside a normal message instead of using the MSC for time time being.. Assuming such additional fields are possible; I don't think anything filters them.

[turt2live]

However, after playing a bit with Element's devtools/add event to timeline I was not able to get Element to render any such event, even after enabling rendering of matrix-org/matrix-spec-proposals#1767 events :/.

Element's support only exists in PR form, and in specific room versions (per the MSC).