Clarify if notifications are cleared by stream ordering or topological ordering

[clokep]

Link to problem area: https://spec.matrix.org/latest/client-server-api/#receiving-notifications

Issue:

It is not stated clearly which notifications get cleared when a read receipt is received, currently the spec reads:

When the user updates their read receipt (either by using the API or by sending an event), notifications prior to and including that event MUST be marked as read.

It is unclear if "prior to" refers to stream ordering or topological ordering. Synapse clears this based on stream ordering.

(Note that because of the inconsistency in /sync and /messages either could give odd results to a user.)

See conversation around https://matrix.to/#/!NasysSDfxKxZBzJJoE:matrix.org/$sb6NPRyuiu4wN7egyY8SJ6YoubvQqZvJSOlMFsTzVSE?via=matrix.org&via=libera.chat&via=element.io

[clokep]

@turt2live Thinks that MSC2285 specifies this properly.

[turt2live]

kinda - I think MSC2285 has words which help clarify how this works rather than solves it.

[clokep]

kinda - I think MSC2285 has words which help clarify how this works rather than solves it.

The spec PR for this doesn't really seem to answer this question still, just uses terms like "before" and "after" to discuss events.