[pseudoIDs] More pseudo ID fixes - Part 2 (#3181)

Fixes include:
- Translating state keys that contain user IDs to their respective room
keys for both querying and sending state events
- **NOTE**: there may be design discussion needed on what should happen
when sender keys cannot be found for users
- A simple fix for kicking guests from rooms properly
- Logic for boundary history visibilities was slightly off (I'm
surprised this only manifested in pseudo ID room versions)

Signed-off-by: `Sam Wedgwood <sam@wedgwood.dev>`

clientapi/routing/state.go

@@ -217,6 +217,37 @@ func OnIncomingStateTypeRequest(
 	var worldReadable bool
 	var wantLatestState bool
 
+	roomVer, err := rsAPI.QueryRoomVersionForRoom(ctx, roomID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: spec.Forbidden(fmt.Sprintf("Unknown room %q or user %q has never joined this room", roomID, device.UserID)),
+		}
+	}
+
+	// Translate user ID state keys to room keys in pseudo ID rooms
+	if roomVer == gomatrixserverlib.RoomVersionPseudoIDs {
+		parsedRoomID, err := spec.NewRoomID(roomID)
+		if err != nil {
+			return util.JSONResponse{
+				Code: http.StatusNotFound,
+				JSON: spec.InvalidParam("invalid room ID"),
+			}
+		}
+		newStateKey, err := synctypes.FromClientStateKey(*parsedRoomID, stateKey, func(roomID spec.RoomID, userID spec.UserID) (*spec.SenderID, error) {
+			return rsAPI.QuerySenderIDForUser(ctx, roomID, userID)
+		})
+		if err != nil {
+			// TODO: work out better logic for failure cases (e.g. sender ID not found)
+			util.GetLogger(ctx).WithError(err).Error("synctypes.FromClientStateKey failed")
+			return util.JSONResponse{
+				Code: http.StatusInternalServerError,
+				JSON: spec.Unknown("internal server error"),
+			}
+		}
+		stateKey = *newStateKey
+	}
+
 	// Always fetch visibility so that we can work out whether to show
 	// the latest events or the last event from when the user was joined.
 	// Then include the requested event type and state key, assuming it