Missing knock->join transition on membership transition graph and table

[richvdh]

Link to problem area:

https://spec.matrix.org/v1.13/client-server-api/#room-membership, https://spec.matrix.org/v1.13/client-server-api/#mroommember

Issue

According to auth rules 4.3.5.3 and 4.3.6 it is legit to transition from knock to join if either (a) the join rule is restricted or knock_restricted and the join request satisfies the restrictions, or (b) the join rule is now public. (In other words, the same as a transition from leave to join.)

This transition is missing from the membership transition graph at https://spec.matrix.org/v1.13/client-server-api/#room-membership; furthermore the table at https://spec.matrix.org/v1.13/client-server-api/#mroommember states "Must never happen" which is flat out wrong.

Expected behaviour

Update the knock -> join transition to be the same as the leave -> join transition.