"state at" is ambiguous

In a whole bunch of places in the CS API and SS API specs, we refer to the "state at" an event, which is ambiguous.

This creates a lot of confusion for homeserver developers. It would be great to make sure that we always refer to either the "state before" (not including changes made by state events) or "state after" (including changes made by state events) an event.

Search the CS API and SS API specifications for every use of “state at” and read the surrounding event-state definitions. Replace each ambiguous reference with either “state before” or “state after,” as appropriate, and consider the work done when no ambiguous “state at” references remain in those specs.

Written by the indexing model from the issue text.