If Riot is unaware of the event for a server-side aggregated edit, it edit doesn't get undone upon redacting

[bwindels]

As of matrix-org/matrix-js-sdk@5d928f0, riot will ignore edit events earlier than the server-side aggregated (SSA) edit, as it should, since the client might not be aware of all edits.

When that SSA edit gets redacted, riot receives the redacting event through sync, but it doesn't have the edit event to redact. It is only aware of the edit because it was SSA onto the original event, the edit event hasn't been received. If the redacted event is not in the part of the timeline Riot is aware of, the redaction doesn't have any effect, and the unsigned/m.relations/m.replace/origin_server_ts on the original event is kept in place, which keeps setting an lower limit for any prior unredacted edits to apply to the original event during local aggregation, causing them to be ignored.

So the aggregation of the original edited event isn't adjusted and the content stays what it was. Clearing the cache and reloading will fix the issue.

[bwindels]

as described in the draft spec for other use cases, we should probably refresh the original event using https://matrix.org/docs/spec/client_server/latest#get-matrix-client-r0-rooms-roomid-event-eventid

we'd need to do this not upon redacting the server-endorsed edit, but upon receiving the redaction for it through sync. E.g. it should be treated in the same way as receiving the original event in the stale_events section during gappy sync.

[bwindels]

I suggest implementing the proposed solution as part of implementing stale_events as described in the MSC. For now redacting the last edit of an event might not always update the message in the timeline until the event happens to be refetched from the server.

See #10330

[jryans]

Tentatively marking this phase 3 so it doesn't get lost, but please adjust as needed.

[bwindels]

Theoretically we could work on this, but it'll be more efficient to do this together with #10330, which is blocked. So marking this as blocked as well.