/send_join response includes unstable prefix for event field

[clokep]

The response generated for /send_join (and parsing of it on the federation client side) still uses an unstable prefix from MSC3083: org.matrix.msc3083.v2.event.

This should be updated to be just event, the stable field name. We probably need to send / handle both for a period of time unfortunately.

See

synapse/synapse/federation/federation_server.py

Line 617 in 98c8fc6

"org.matrix.msc3083.v2.event": event.get_pdu_json(),

[clokep]

This should not have been closed -- #11413 added the stable field but did not remove the unstable field.

[clokep]

Note that the proper field landed in Synapse v1.49.0, release 2021-12-21.

[clokep]

Note that Synapse v1.41.0 had support for room version 8, and Synapse v1.42.0 had support for room version 9; both of which could use the fields from above.