Sticky event support is missing spec

[robintown]

#152 added support for sending sticky events in widgets and element-hq/element-web#31205 added support for receiving them. However this functionality doesn't seem to be specced anywhere yet. I would expect to see the details added to MSC2762 or an entirely new MSC.

[robintown]

Timo has drafted a spec at MSC4407. To-do: Review for completeness

[toger5]

@fkwp @BillCarsonFr if you can give the msc a review we can undraft the MSC and close this issue.

[fkwp]

@fkwp @BillCarsonFr if you can give the msc a review we can undraft the MSC and close this issue.

lgtm. Should we also address the replaying of the sticky map? Or is this included in the "allowed events" phrase?

[toger5]

It is included here:

Widget Client Implementation

This has the following behavioral impact on the widget client implementation:

• On widget startup, the client will send all sticky events that the widget is allowed to see.
• After capability re-negotiation, when the widget is granted m.receive.sticky_event, the client will send all currently sticky events that the widget is allowed to see.

If the capability m.send.sticky_event is granted and the client receives a send event with sticky_duration_ms set, the client must send a sticky event as described in matrix-org/matrix-spec-proposals#4354, using the sticky_duration_ms.

I updated it to explicitly mention the capability this relates to.

Widget Client Implementation

If a widget is granted the m.receive.sticky_event capability, the host client must do the following:

• On widget startup, the client will send all sticky events that the widget is allowed to see.
• After capability re-negotiation, when the widget is now granted m.receive.sticky_event and was not before, the client will send all currently sticky events that the widget is allowed to see.

If the capability m.send.sticky_event is granted and the client receives a send event with sticky_duration_ms set, the client must send a sticky event
as described in MSC4354, using the sticky_duration_ms.

[fkwp]

nice