diff --git a/src/RTCConnectionStats.tsx b/src/RTCConnectionStats.tsx
index dcd8d019..d51089cf 100644
--- a/src/RTCConnectionStats.tsx
+++ b/src/RTCConnectionStats.tsx
@@ -19,10 +19,26 @@ import mediaViewStyles from "../src/tile/MediaView.module.css";
 interface Props {
   audio?: RTCInboundRtpStreamStats | RTCOutboundRtpStreamStats;
   video?: RTCInboundRtpStreamStats | RTCOutboundRtpStreamStats;
+  focusUrl?: string;
 }
 
+const extractDomain = (url: string): string => {
+  try {
+    const parsedUrl = new URL(url);
+    return parsedUrl.hostname; // Returns "kdk.cpm"
+  } catch (error) {
+    console.error("Invalid URL:", error);
+    return url;
+  }
+};
+
 // This is only used in developer mode for debugging purposes, so we don't need full localization
-export const RTCConnectionStats: FC<Props> = ({ audio, video, ...rest }) => {
+export const RTCConnectionStats: FC<Props> = ({
+  audio,
+  video,
+  focusUrl,
+  ...rest
+}) => {
   const [showModal, setShowModal] = useState(false);
   const [modalContents, setModalContents] = useState<
     "video" | "audio" | "none"
@@ -55,6 +71,13 @@ export const RTCConnectionStats: FC<Props> = ({ audio, video, ...rest }) => {
           </pre>
         </div>
       </Modal>
+      {focusUrl && (
+        <div>
+          <Text as="span" size="xs" title="focusURL">
+            &nbsp;{extractDomain(focusUrl)}
+          </Text>
+        </div>
+      )}
       {audio && (
         <div>
           <Button
diff --git a/src/button/ReactionToggleButton.test.tsx b/src/button/ReactionToggleButton.test.tsx
index b1af7ec8..1ac43ebc 100644
--- a/src/button/ReactionToggleButton.test.tsx
+++ b/src/button/ReactionToggleButton.test.tsx
@@ -19,7 +19,7 @@ import { alice, local, localRtcMember } from "../utils/test-fixtures";
 import { type MockRTCSession } from "../utils/test";
 import { ReactionsSenderProvider } from "../reactions/useReactionsSender";
 
-const localIdent = `${localRtcMember.sender}:${localRtcMember.deviceId}`;
+const localIdent = `${localRtcMember.userId}:${localRtcMember.deviceId}`;
 
 function TestComponent({
   rtcSession,
diff --git a/src/grid/GridLayout.tsx b/src/grid/GridLayout.tsx
index 51fbc6ea..cf46e8b4 100644
--- a/src/grid/GridLayout.tsx
+++ b/src/grid/GridLayout.tsx
@@ -14,7 +14,7 @@ import {
 import { distinctUntilChanged } from "rxjs";
 import { useObservableEagerState } from "observable-hooks";
 
-import { type GridLayout as GridLayoutModel } from "../state/CallViewModel";
+import { type GridLayout as GridLayoutModel } from "../state/layout-types.ts";
 import styles from "./GridLayout.module.css";
 import { useInitial } from "../useInitial";
 import { type CallLayout, arrangeTiles } from "./CallLayout";
diff --git a/src/grid/OneOnOneLayout.tsx b/src/grid/OneOnOneLayout.tsx
index 675e4d0a..6c5ae69f 100644
--- a/src/grid/OneOnOneLayout.tsx
+++ b/src/grid/OneOnOneLayout.tsx
@@ -9,7 +9,7 @@ import { type ReactNode, useCallback, useMemo } from "react";
 import { useObservableEagerState } from "observable-hooks";
 import classNames from "classnames";
 
-import { type OneOnOneLayout as OneOnOneLayoutModel } from "../state/CallViewModel";
+import { type OneOnOneLayout as OneOnOneLayoutModel } from "../state/layout-types.ts";
 import { type CallLayout, arrangeTiles } from "./CallLayout";
 import styles from "./OneOnOneLayout.module.css";
 import { type DragCallback, useUpdateLayout } from "./Grid";
diff --git a/src/grid/SpotlightExpandedLayout.tsx b/src/grid/SpotlightExpandedLayout.tsx
index 9dd2a109..ac47f0d4 100644
--- a/src/grid/SpotlightExpandedLayout.tsx
+++ b/src/grid/SpotlightExpandedLayout.tsx
@@ -7,7 +7,7 @@ Please see LICENSE in the repository root for full details.
 
 import { type ReactNode, useCallback } from "react";
 
-import { type SpotlightExpandedLayout as SpotlightExpandedLayoutModel } from "../state/CallViewModel";
+import { type SpotlightExpandedLayout as SpotlightExpandedLayoutModel } from "../state/layout-types.ts";
 import { type CallLayout } from "./CallLayout";
 import { type DragCallback, useUpdateLayout } from "./Grid";
 import styles from "./SpotlightExpandedLayout.module.css";
diff --git a/src/grid/SpotlightLandscapeLayout.tsx b/src/grid/SpotlightLandscapeLayout.tsx
index 96343296..d87be1f1 100644
--- a/src/grid/SpotlightLandscapeLayout.tsx
+++ b/src/grid/SpotlightLandscapeLayout.tsx
@@ -10,7 +10,7 @@ import { useObservableEagerState } from "observable-hooks";
 import classNames from "classnames";
 
 import { type CallLayout } from "./CallLayout";
-import { type SpotlightLandscapeLayout as SpotlightLandscapeLayoutModel } from "../state/CallViewModel";
+import { type SpotlightLandscapeLayout as SpotlightLandscapeLayoutModel } from "../state/layout-types.ts";
 import styles from "./SpotlightLandscapeLayout.module.css";
 import { useUpdateLayout, useVisibleTiles } from "./Grid";
 
diff --git a/src/grid/SpotlightPortraitLayout.tsx b/src/grid/SpotlightPortraitLayout.tsx
index ad11ed11..a6d1241c 100644
--- a/src/grid/SpotlightPortraitLayout.tsx
+++ b/src/grid/SpotlightPortraitLayout.tsx
@@ -10,7 +10,7 @@ import { useObservableEagerState } from "observable-hooks";
 import classNames from "classnames";
 
 import { type CallLayout, arrangeTiles } from "./CallLayout";
-import { type SpotlightPortraitLayout as SpotlightPortraitLayoutModel } from "../state/CallViewModel";
+import { type SpotlightPortraitLayout as SpotlightPortraitLayoutModel } from "../state/layout-types.ts";
 import styles from "./SpotlightPortraitLayout.module.css";
 import { useUpdateLayout, useVisibleTiles } from "./Grid";
 import { useBehavior } from "../useBehavior";
diff --git a/src/reactions/ReactionsReader.test.tsx b/src/reactions/ReactionsReader.test.tsx
index 01815c82..76ea45be 100644
--- a/src/reactions/ReactionsReader.test.tsx
+++ b/src/reactions/ReactionsReader.test.tsx
@@ -47,7 +47,7 @@ test("handles a hand raised reaction", () => {
             new MatrixEvent({
               room_id: rtcSession.room.roomId,
               event_id: reactionEventId,
-              sender: localRtcMember.sender,
+              sender: localRtcMember.userId,
               type: EventType.Reaction,
               origin_server_ts: localTimestamp.getTime(),
               content: {
@@ -67,7 +67,7 @@ test("handles a hand raised reaction", () => {
       expectObservable(raisedHands$).toBe("ab", {
         a: {},
         b: {
-          [`${localRtcMember.sender}:${localRtcMember.deviceId}`]: {
+          [`${localRtcMember.userId}:${localRtcMember.deviceId}`]: {
             reactionEventId,
             membershipEventId: localRtcMember.eventId,
             time: localTimestamp,
@@ -95,7 +95,7 @@ test("handles a redaction", () => {
             new MatrixEvent({
               room_id: rtcSession.room.roomId,
               event_id: reactionEventId,
-              sender: localRtcMember.sender,
+              sender: localRtcMember.userId,
               type: EventType.Reaction,
               origin_server_ts: localTimestamp.getTime(),
               content: {
@@ -117,7 +117,7 @@ test("handles a redaction", () => {
             new MatrixEvent({
               room_id: rtcSession.room.roomId,
               event_id: reactionEventId,
-              sender: localRtcMember.sender,
+              sender: localRtcMember.userId,
               type: EventType.RoomRedaction,
               redacts: reactionEventId,
             }),
@@ -129,7 +129,7 @@ test("handles a redaction", () => {
       expectObservable(raisedHands$).toBe("abc", {
         a: {},
         b: {
-          [`${localRtcMember.sender}:${localRtcMember.deviceId}`]: {
+          [`${localRtcMember.userId}:${localRtcMember.deviceId}`]: {
             reactionEventId,
             membershipEventId: localRtcMember.eventId,
             time: localTimestamp,
@@ -156,7 +156,7 @@ test("handles waiting for event decryption", () => {
           const encryptedEvent = new MatrixEvent({
             room_id: rtcSession.room.roomId,
             event_id: reactionEventId,
-            sender: localRtcMember.sender,
+            sender: localRtcMember.userId,
             type: EventType.Reaction,
             origin_server_ts: localTimestamp.getTime(),
             content: {
@@ -183,7 +183,7 @@ test("handles waiting for event decryption", () => {
             new MatrixEvent({
               room_id: rtcSession.room.roomId,
               event_id: reactionEventId,
-              sender: localRtcMember.sender,
+              sender: localRtcMember.userId,
               type: EventType.Reaction,
               origin_server_ts: localTimestamp.getTime(),
               content: {
@@ -199,7 +199,7 @@ test("handles waiting for event decryption", () => {
       expectObservable(raisedHands$).toBe("a-c", {
         a: {},
         c: {
-          [`${localRtcMember.sender}:${localRtcMember.deviceId}`]: {
+          [`${localRtcMember.userId}:${localRtcMember.deviceId}`]: {
             reactionEventId,
             membershipEventId: localRtcMember.eventId,
             time: localTimestamp,
@@ -227,7 +227,7 @@ test("hands rejecting events without a proper membership", () => {
             new MatrixEvent({
               room_id: rtcSession.room.roomId,
               event_id: reactionEventId,
-              sender: localRtcMember.sender,
+              sender: localRtcMember.userId,
               type: EventType.Reaction,
               origin_server_ts: localTimestamp.getTime(),
               content: {
@@ -270,7 +270,7 @@ test("handles a reaction", () => {
             new MatrixEvent({
               room_id: rtcSession.room.roomId,
               event_id: reactionEventId,
-              sender: localRtcMember.sender,
+              sender: localRtcMember.userId,
               type: ElementCallReactionEventType,
               content: {
                 emoji: reaction.emoji,
@@ -295,7 +295,7 @@ test("handles a reaction", () => {
         {
           a: {},
           b: {
-            [`${localRtcMember.sender}:${localRtcMember.deviceId}`]: {
+            [`${localRtcMember.userId}:${localRtcMember.deviceId}`]: {
               reactionOption: reaction,
               expireAfter: new Date(REACTION_ACTIVE_TIME_MS),
             },
@@ -327,7 +327,7 @@ test("ignores bad reaction events", () => {
             new MatrixEvent({
               room_id: rtcSession.room.roomId,
               event_id: reactionEventId,
-              sender: localRtcMember.sender,
+              sender: localRtcMember.userId,
               type: ElementCallReactionEventType,
               content: {},
             }),
@@ -342,7 +342,7 @@ test("ignores bad reaction events", () => {
             new MatrixEvent({
               room_id: rtcSession.room.roomId,
               event_id: reactionEventId,
-              sender: localRtcMember.sender,
+              sender: localRtcMember.userId,
               type: ElementCallReactionEventType,
               content: {
                 emoji: reaction.emoji,
@@ -363,7 +363,7 @@ test("ignores bad reaction events", () => {
             new MatrixEvent({
               room_id: rtcSession.room.roomId,
               event_id: reactionEventId,
-              sender: aliceRtcMember.sender,
+              sender: aliceRtcMember.userId,
               type: ElementCallReactionEventType,
               content: {
                 emoji: reaction.emoji,
@@ -384,7 +384,7 @@ test("ignores bad reaction events", () => {
             new MatrixEvent({
               room_id: rtcSession.room.roomId,
               event_id: reactionEventId,
-              sender: localRtcMember.sender,
+              sender: localRtcMember.userId,
               type: ElementCallReactionEventType,
               content: {
                 name: reaction.name,
@@ -404,7 +404,7 @@ test("ignores bad reaction events", () => {
             new MatrixEvent({
               room_id: rtcSession.room.roomId,
               event_id: reactionEventId,
-              sender: localRtcMember.sender,
+              sender: localRtcMember.userId,
               type: ElementCallReactionEventType,
               content: {
                 emoji: " ",
@@ -448,7 +448,7 @@ test("that reactions cannot be spammed", () => {
             new MatrixEvent({
               room_id: rtcSession.room.roomId,
               event_id: reactionEventId,
-              sender: localRtcMember.sender,
+              sender: localRtcMember.userId,
               type: ElementCallReactionEventType,
               content: {
                 emoji: reactionA.emoji,
@@ -470,7 +470,7 @@ test("that reactions cannot be spammed", () => {
             new MatrixEvent({
               room_id: rtcSession.room.roomId,
               event_id: reactionEventId,
-              sender: localRtcMember.sender,
+              sender: localRtcMember.userId,
               type: ElementCallReactionEventType,
               content: {
                 emoji: reactionB.emoji,
@@ -495,7 +495,7 @@ test("that reactions cannot be spammed", () => {
         {
           a: {},
           b: {
-            [`${localRtcMember.sender}:${localRtcMember.deviceId}`]: {
+            [`${localRtcMember.userId}:${localRtcMember.deviceId}`]: {
               reactionOption: reactionA,
               expireAfter: new Date(REACTION_ACTIVE_TIME_MS),
             },
diff --git a/src/reactions/ReactionsReader.ts b/src/reactions/ReactionsReader.ts
index b630f4b9..9e30eff5 100644
--- a/src/reactions/ReactionsReader.ts
+++ b/src/reactions/ReactionsReader.ts
@@ -130,7 +130,7 @@ export class ReactionsReader {
   private onMembershipsChanged = (oldMemberships: CallMembership[]): void => {
     // Remove any raised hands for users no longer joined to the call.
     for (const identifier of Object.keys(this.raisedHandsSubject$.value).filter(
-      (rhId) => oldMemberships.find((u) => u.sender == rhId),
+      (rhId) => oldMemberships.find((u) => u.userId == rhId),
     )) {
       this.removeRaisedHand(identifier);
     }
@@ -138,10 +138,10 @@ export class ReactionsReader {
     // For each member in the call, check to see if a reaction has
     // been raised and adjust.
     for (const m of this.rtcSession.memberships) {
-      if (!m.sender || !m.eventId) {
+      if (!m.userId || !m.eventId) {
         continue;
       }
-      const identifier = `${m.sender}:${m.deviceId}`;
+      const identifier = `${m.userId}:${m.deviceId}`;
       if (
         this.raisedHandsSubject$.value[identifier] &&
         this.raisedHandsSubject$.value[identifier].membershipEventId !==
@@ -151,13 +151,13 @@ export class ReactionsReader {
         // was raised, reset.
         this.removeRaisedHand(identifier);
       }
-      const reaction = this.getLastReactionEvent(m.eventId, m.sender);
+      const reaction = this.getLastReactionEvent(m.eventId, m.userId);
       if (reaction) {
         const eventId = reaction?.getId();
         if (!eventId) {
           continue;
         }
-        this.addRaisedHand(`${m.sender}:${m.deviceId}`, {
+        this.addRaisedHand(`${m.userId}:${m.deviceId}`, {
           membershipEventId: m.eventId,
           reactionEventId: eventId,
           time: new Date(reaction.localTimestamp),
@@ -219,7 +219,7 @@ export class ReactionsReader {
 
       const membershipEventId = content?.["m.relates_to"]?.event_id;
       const membershipEvent = this.rtcSession.memberships.find(
-        (e) => e.eventId === membershipEventId && e.sender === sender,
+        (e) => e.eventId === membershipEventId && e.userId === sender,
       );
       // Check to see if this reaction was made to a membership event (and the
       // sender of the reaction matches the membership)
@@ -229,7 +229,7 @@ export class ReactionsReader {
         );
         return;
       }
-      const identifier = `${membershipEvent.sender}:${membershipEvent.deviceId}`;
+      const identifier = `${membershipEvent.userId}:${membershipEvent.deviceId}`;
 
       if (!content.emoji) {
         logger.warn(`Reaction had no emoji from ${reactionEventId}`);
@@ -278,7 +278,7 @@ export class ReactionsReader {
       // Check to see if this reaction was made to a membership event (and the
       // sender of the reaction matches the membership)
       const membershipEvent = this.rtcSession.memberships.find(
-        (e) => e.eventId === membershipEventId && e.sender === sender,
+        (e) => e.eventId === membershipEventId && e.userId === sender,
       );
       if (!membershipEvent) {
         logger.warn(
@@ -289,7 +289,7 @@ export class ReactionsReader {
 
       if (content?.["m.relates_to"].key === "🖐️") {
         this.addRaisedHand(
-          `${membershipEvent.sender}:${membershipEvent.deviceId}`,
+          `${membershipEvent.userId}:${membershipEvent.deviceId}`,
           {
             reactionEventId,
             membershipEventId,
diff --git a/src/reactions/useReactionsSender.tsx b/src/reactions/useReactionsSender.tsx
index 5f509a0c..ec29c2af 100644
--- a/src/reactions/useReactionsSender.tsx
+++ b/src/reactions/useReactionsSender.tsx
@@ -65,7 +65,7 @@ export const ReactionsSenderProvider = ({
   const myMembershipEvent = useMemo(
     () =>
       memberships.find(
-        (m) => m.sender === myUserId && m.deviceId === myDeviceId,
+        (m) => m.userId === myUserId && m.deviceId === myDeviceId,
       )?.eventId,
     [memberships, myUserId, myDeviceId],
   );
diff --git a/src/room/CallEventAudioRenderer.test.tsx b/src/room/CallEventAudioRenderer.test.tsx
index e7d7e85a..bc1a1b39 100644
--- a/src/room/CallEventAudioRenderer.test.tsx
+++ b/src/room/CallEventAudioRenderer.test.tsx
@@ -156,7 +156,7 @@ test("plays one sound when a hand is raised", () => {
   act(() => {
     handRaisedSubject$.next({
       // TODO: What is this string supposed to be?
-      [`${bobRtcMember.sender}:${bobRtcMember.deviceId}`]: {
+      [`${bobRtcMember.userId}:${bobRtcMember.deviceId}`]: {
         time: new Date(),
         membershipEventId: "",
         reactionEventId: "",
diff --git a/src/room/GroupCallView.test.tsx b/src/room/GroupCallView.test.tsx
index 37f5c850..a96a9c7d 100644
--- a/src/room/GroupCallView.test.tsx
+++ b/src/room/GroupCallView.test.tsx
@@ -122,7 +122,7 @@ function createGroupCallView(
 } {
   const client = {
     getUser: () => null,
-    getUserId: () => localRtcMember.sender,
+    getUserId: () => localRtcMember.userId,
     getDeviceId: () => localRtcMember.deviceId,
     getRoom: (rId) => (rId === roomId ? room : null),
   } as Partial<MatrixClient> as MatrixClient;
diff --git a/src/room/GroupCallView.tsx b/src/room/GroupCallView.tsx
index a9c31150..1359b003 100644
--- a/src/room/GroupCallView.tsx
+++ b/src/room/GroupCallView.tsx
@@ -207,7 +207,7 @@ export const GroupCallView: FC<Props> = ({
 
   // Count each member only once, regardless of how many devices they use
   const participantCount = useMemo(
-    () => new Set<string>(memberships.map((m) => m.sender!)).size,
+    () => new Set<string>(memberships.map((m) => m.userId!)).size,
     [memberships],
   );
 
diff --git a/src/room/InCallView.test.tsx b/src/room/InCallView.test.tsx
index 1caa3e3d..d75fd598 100644
--- a/src/room/InCallView.test.tsx
+++ b/src/room/InCallView.test.tsx
@@ -110,7 +110,7 @@ function createInCallView(): RenderResult & {
 } {
   const client = {
     getUser: () => null,
-    getUserId: () => localRtcMember.sender,
+    getUserId: () => localRtcMember.userId,
     getDeviceId: () => localRtcMember.deviceId,
     getRoom: (rId) => (rId === roomId ? room : null),
   } as Partial<MatrixClient> as MatrixClient;
diff --git a/src/room/InCallView.tsx b/src/room/InCallView.tsx
index fd631bae..6b07dacc 100644
--- a/src/room/InCallView.tsx
+++ b/src/room/InCallView.tsx
@@ -59,11 +59,7 @@ import { type MuteStates } from "../state/MuteStates";
 import { type MatrixInfo } from "./VideoPreview";
 import { InviteButton } from "../button/InviteButton";
 import { LayoutToggle } from "./LayoutToggle";
-import {
-  CallViewModel,
-  type GridMode,
-  type Layout,
-} from "../state/CallViewModel";
+import { CallViewModel, type GridMode } from "../state/CallViewModel";
 import { Grid, type TileProps } from "../grid/Grid";
 import { useInitial } from "../useInitial";
 import { SpotlightTile } from "../tile/SpotlightTile";
@@ -113,6 +109,7 @@ import { useAudioContext } from "../useAudioContext";
 import ringtoneMp3 from "../sound/ringtone.mp3?url";
 import ringtoneOgg from "../sound/ringtone.ogg?url";
 import { useTrackProcessorObservable$ } from "../livekit/TrackProcessorContext.tsx";
+import { type Layout } from "../state/layout-types.ts";
 
 const maxTapDurationMs = 400;
 
@@ -300,6 +297,10 @@ export const InCallView: FC<InCallViewProps> = ({
   const audioOutputSwitcher = useBehavior(vm.audioOutputSwitcher$);
   const sharingScreen = useBehavior(vm.sharingScreen$);
 
+  const fatalCallError = useBehavior(vm.configError$);
+  // Stop the rendering and throw for the error boundary
+  if (fatalCallError) throw fatalCallError;
+
   // We need to set the proper timings on the animation based upon the sound length.
   const ringDuration = pickupPhaseAudio?.soundDuration["waiting"] ?? 1;
   useEffect((): (() => void) => {
diff --git a/src/rtcSessionHelpers.test.ts b/src/rtcSessionHelpers.test.ts
index b2caaf89..2ac61480 100644
--- a/src/rtcSessionHelpers.test.ts
+++ b/src/rtcSessionHelpers.test.ts
@@ -13,8 +13,8 @@ import EventEmitter from "events";
 import { enterRTCSession, leaveRTCSession } from "../src/rtcSessionHelpers";
 import { mockConfig } from "./utils/test";
 import { ElementWidgetActions, widget } from "./widget";
-import { ErrorCode } from "./utils/errors.ts";
 
+const USE_MUTI_SFU = false;
 const getUrlParams = vi.hoisted(() => vi.fn(() => ({})));
 vi.mock("./UrlParams", () => ({ getUrlParams }));
 
@@ -93,41 +93,26 @@ test("It joins the correct Session", async () => {
       livekit_service_url: "http://my-well-known-service-url.com",
       type: "livekit",
     },
-    true,
+    {
+      encryptMedia: true,
+      useMultiSfu: USE_MUTI_SFU,
+    },
   );
 
   expect(mockedSession.joinRoomSession).toHaveBeenLastCalledWith(
     [
-      {
-        livekit_alias: "my-oldest-member-service-alias",
-        livekit_service_url: "http://my-oldest-member-service-url.com",
-        type: "livekit",
-      },
       {
         livekit_alias: "roomId",
         livekit_service_url: "http://my-well-known-service-url.com",
         type: "livekit",
       },
-      {
-        livekit_alias: "roomId",
-        livekit_service_url: "http://my-well-known-service-url2.com",
-        type: "livekit",
-      },
-      {
-        livekit_alias: "roomId",
-        livekit_service_url: "http://my-default-service-url.com",
-        type: "livekit",
-      },
     ],
-    {
-      focus_selection: "oldest_membership",
-      type: "livekit",
-    },
-    {
-      manageMediaKeys: false,
+    undefined,
+    expect.objectContaining({
+      manageMediaKeys: true,
       useLegacyMemberEvents: false,
       useExperimentalToDeviceTransport: false,
-    },
+    }),
   );
 });
 
@@ -172,37 +157,6 @@ test("leaveRTCSession doesn't close the widget when returning to lobby", async (
   await testLeaveRTCSession("user", false);
 });
 
-test("It fails with configuration error if no live kit url config is set in fallback", async () => {
-  mockConfig({});
-  vi.spyOn(AutoDiscovery, "getRawClientConfig").mockResolvedValue({});
-
-  const mockedSession = vi.mocked({
-    room: {
-      roomId: "roomId",
-      client: {
-        getDomain: vi.fn().mockReturnValue("example.org"),
-      },
-    },
-    memberships: [],
-    getFocusInUse: vi.fn(),
-    joinRoomSession: vi.fn(),
-  }) as unknown as MatrixRTCSession;
-
-  await expect(
-    enterRTCSession(
-      mockedSession,
-      {
-        livekit_alias: "roomId",
-        livekit_service_url: "http://my-well-known-service-url.com",
-        type: "livekit",
-      },
-      true,
-    ),
-  ).rejects.toThrowError(
-    expect.objectContaining({ code: ErrorCode.MISSING_MATRIX_RTC_TRANSPORT }),
-  );
-});
-
 test("It should not fail with configuration error if homeserver config has livekit url but not fallback", async () => {
   mockConfig({});
   vi.spyOn(AutoDiscovery, "getRawClientConfig").mockResolvedValue({
@@ -239,6 +193,9 @@ test("It should not fail with configuration error if homeserver config has livek
       livekit_service_url: "http://my-well-known-service-url.com",
       type: "livekit",
     },
-    true,
+    {
+      encryptMedia: true,
+      useMultiSfu: USE_MUTI_SFU,
+    },
   );
 });
diff --git a/src/rtcSessionHelpers.ts b/src/rtcSessionHelpers.ts
index b80c8efd..27a0aeb2 100644
--- a/src/rtcSessionHelpers.ts
+++ b/src/rtcSessionHelpers.ts
@@ -98,13 +98,37 @@ export async function makeTransport(
   return transport;
 }
 
+export interface EnterRTCSessionOptions {
+  encryptMedia: boolean;
+  // TODO: remove this flag, the new membership manager is stable enough
+  useNewMembershipManager?: boolean;
+  // TODO: remove this flag, to-device transport is stable enough now
+  useExperimentalToDeviceTransport?: boolean;
+  /** EXPERIMENTAL: If true, will use the multi-sfu codepath where each member connects to its SFU instead of everyone connecting to an elected on. */
+  useMultiSfu?: boolean;
+}
+
+/**
+ * TODO! document this function properly
+ * @param rtcSession
+ * @param transport
+ * @param options
+ */
 export async function enterRTCSession(
   rtcSession: MatrixRTCSession,
   transport: LivekitTransport,
-  encryptMedia: boolean,
-  useExperimentalToDeviceTransport = false,
-  useMultiSfu = true,
+  options: EnterRTCSessionOptions = {
+    encryptMedia: true,
+    useExperimentalToDeviceTransport: false,
+    useMultiSfu: true,
+  },
 ): Promise<void> {
+  const {
+    encryptMedia,
+    useExperimentalToDeviceTransport = false,
+    useMultiSfu = true,
+  } = options;
+
   PosthogAnalytics.instance.eventCallEnded.cacheStartCall(new Date());
   PosthogAnalytics.instance.eventCallStarted.track(rtcSession.room.roomId);
 
diff --git a/src/state/CallViewModel.test.ts b/src/state/CallViewModel.test.ts
index 055720c8..52d13ca4 100644
--- a/src/state/CallViewModel.test.ts
+++ b/src/state/CallViewModel.test.ts
@@ -5,7 +5,7 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { test, vi, onTestFinished, it, describe } from "vitest";
+import { test, vi, onTestFinished, it, describe, expect } from "vitest";
 import EventEmitter from "events";
 import {
   BehaviorSubject,
@@ -45,12 +45,10 @@ import {
   MatrixRTCSessionEvent,
 } from "matrix-js-sdk/lib/matrixrtc";
 import { deepCompare } from "matrix-js-sdk/lib/utils";
+import { AutoDiscovery } from "matrix-js-sdk/lib/autodiscovery";
 
-import {
-  CallViewModel,
-  type CallViewModelOptions,
-  type Layout,
-} from "./CallViewModel";
+import { CallViewModel, type CallViewModelOptions } from "./CallViewModel";
+import { type Layout } from "./layout-types";
 import {
   mockLocalParticipant,
   mockMatrixRoom,
@@ -61,6 +59,7 @@ import {
   MockRTCSession,
   mockMediaDevices,
   mockMuteStates,
+  mockConfig,
 } from "../utils/test";
 import {
   ECAddonConnectionState,
@@ -95,6 +94,10 @@ import { MediaDevices } from "./MediaDevices";
 import { getValue } from "../utils/observable";
 import { type Behavior, constant } from "./Behavior";
 import type { ProcessorState } from "../livekit/TrackProcessorContext.tsx";
+import {
+  type ElementCallError,
+  MatrixRTCTransportMissingError,
+} from "../utils/errors.ts";
 
 const getUrlParams = vi.hoisted(() => vi.fn(() => ({})));
 vi.mock("../UrlParams", () => ({ getUrlParams }));
@@ -302,7 +305,7 @@ function withCallViewModel(
   const room = mockMatrixRoom({
     client: new (class extends EventEmitter {
       public getUserId(): string | undefined {
-        return localRtcMember.sender;
+        return localRtcMember.userId;
       }
       public getDeviceId(): string {
         return localRtcMember.deviceId;
@@ -368,6 +371,61 @@ function withCallViewModel(
   continuation(vm, rtcSession, { raisedHands$: raisedHands$ }, setSyncState);
 }
 
+test("test missing RTC config error", async () => {
+  const rtcMemberships$ = new BehaviorSubject<CallMembership[]>([]);
+  const emitter = new EventEmitter();
+  const client = vi.mocked<MatrixClient>({
+    on: emitter.on.bind(emitter),
+    off: emitter.off.bind(emitter),
+    getSyncState: vi.fn().mockReturnValue(SyncState.Syncing),
+    getUserId: vi.fn().mockReturnValue("@user:localhost"),
+    getUser: vi.fn().mockReturnValue(null),
+    getDeviceId: vi.fn().mockReturnValue("DEVICE"),
+    credentials: {
+      userId: "@user:localhost",
+    },
+    getCrypto: vi.fn().mockReturnValue(undefined),
+    getDomain: vi.fn().mockReturnValue("example.org"),
+  } as unknown as MatrixClient);
+
+  const matrixRoom = mockMatrixRoom({
+    roomId: "!myRoomId:example.com",
+    client,
+    getMember: vi.fn().mockReturnValue(undefined),
+  });
+
+  const fakeRtcSession = new MockRTCSession(matrixRoom).withMemberships(
+    rtcMemberships$,
+  );
+
+  mockConfig({});
+  vi.spyOn(AutoDiscovery, "getRawClientConfig").mockResolvedValue({});
+
+  const callVM = new CallViewModel(
+    fakeRtcSession.asMockedSession(),
+    matrixRoom,
+    mockMediaDevices({}),
+    mockMuteStates(),
+    {
+      encryptionSystem: { kind: E2eeType.PER_PARTICIPANT },
+      autoLeaveWhenOthersLeft: false,
+    },
+    new BehaviorSubject({} as Record<string, RaisedHandInfo>),
+    new BehaviorSubject({} as Record<string, ReactionInfo>),
+    of({ processor: undefined, supported: false }),
+  );
+
+  const failPromise = Promise.withResolvers<ElementCallError>();
+  callVM.configError$.subscribe((error) => {
+    if (error) {
+      failPromise.resolve(error);
+    }
+  });
+
+  const error = await failPromise.promise;
+  expect(error).toBeInstanceOf(MatrixRTCTransportMissingError);
+});
+
 test("participants are retained during a focus switch", () => {
   withTestScheduler(({ behavior, expectObservable }) => {
     // Participants disappear on frame 2 and come back on frame 3
@@ -1012,7 +1070,7 @@ it("should rank raised hands above video feeds and below speakers and presenters
           },
           b: () => {
             raisedHands$.next({
-              [`${bobRtcMember.sender}:${bobRtcMember.deviceId}`]: {
+              [`${bobRtcMember.userId}:${bobRtcMember.deviceId}`]: {
                 time: new Date(),
                 reactionEventId: "",
                 membershipEventId: "",
diff --git a/src/state/CallViewModel.ts b/src/state/CallViewModel.ts
index b2f6a464..6b046b28 100644
--- a/src/state/CallViewModel.ts
+++ b/src/state/CallViewModel.ts
@@ -5,39 +5,33 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { observeParticipantEvents } from "@livekit/components-core";
 import {
-  ConnectionState,
   type BaseKeyProvider,
+  ConnectionState,
   type E2EEOptions,
   ExternalE2EEKeyProvider,
-  type Room as LivekitRoom,
   type LocalParticipant,
-  ParticipantEvent,
   RemoteParticipant,
-  type Participant,
+  type Room as LivekitRoom,
 } from "livekit-client";
 import E2EEWorker from "livekit-client/e2ee-worker?worker";
 import {
   ClientEvent,
+  type EventTimelineSetHandlerMap,
+  EventType,
+  type Room as MatrixRoom,
+  RoomEvent,
   type RoomMember,
   RoomStateEvent,
   SyncState,
-  type Room as MatrixRoom,
-  type EventTimelineSetHandlerMap,
-  EventType,
-  RoomEvent,
 } from "matrix-js-sdk";
 import { deepCompare } from "matrix-js-sdk/lib/utils";
 import {
   BehaviorSubject,
-  EMPTY,
-  NEVER,
-  type Observable,
-  Subject,
   combineLatest,
   concat,
   distinctUntilChanged,
+  EMPTY,
   endWith,
   filter,
   from,
@@ -45,6 +39,8 @@ import {
   ignoreElements,
   map,
   merge,
+  NEVER,
+  type Observable,
   of,
   pairwise,
   race,
@@ -53,6 +49,7 @@ import {
   skip,
   skipWhile,
   startWith,
+  Subject,
   switchAll,
   switchMap,
   switchScan,
@@ -80,7 +77,7 @@ import { ViewModel } from "./ViewModel";
 import {
   LocalUserMediaViewModel,
   type MediaViewModel,
-  RemoteUserMediaViewModel,
+  type RemoteUserMediaViewModel,
   ScreenShareViewModel,
   type UserMediaViewModel,
 } from "./MediaViewModel";
@@ -90,7 +87,6 @@ import {
   finalizeValue,
   pauseWhen,
 } from "../utils/observable";
-import { ObservableScope } from "./ObservableScope";
 import {
   duplicateTiles,
   multiSfu,
@@ -99,10 +95,6 @@ import {
 } from "../settings/settings";
 import { isFirefox } from "../Platform";
 import { setPipEnabled$ } from "../controls";
-import {
-  type GridTileViewModel,
-  type SpotlightTileViewModel,
-} from "./TileViewModel";
 import { TileStore } from "./TileStore";
 import { gridLikeLayout } from "./GridLikeLayout";
 import { spotlightExpandedLayout } from "./SpotlightExpandedLayout";
@@ -114,11 +106,10 @@ import {
   type ReactionInfo,
   type ReactionOption,
 } from "../reactions";
-import { observeSpeaker$ } from "./observeSpeaker";
 import { shallowEquals } from "../utils/array";
 import { calculateDisplayName, shouldDisambiguate } from "../utils/displayname";
 import { type MediaDevices } from "./MediaDevices";
-import { constant, type Behavior } from "./Behavior";
+import { type Behavior, constant } from "./Behavior";
 import {
   enterRTCSession,
   getLivekitAlias,
@@ -137,6 +128,19 @@ import { type ProcessorState } from "../livekit/TrackProcessorContext";
 import { ElementWidgetActions, widget } from "../widget";
 import { PublishConnection } from "./PublishConnection.ts";
 import { type Async, async$, mapAsync, ready } from "./Async";
+import { sharingScreen$, UserMedia } from "./UserMedia.ts";
+import { ScreenShare } from "./ScreenShare.ts";
+import {
+  type GridLayoutMedia,
+  type Layout,
+  type LayoutMedia,
+  type OneOnOneLayoutMedia,
+  type SpotlightExpandedLayoutMedia,
+  type SpotlightLandscapeLayoutMedia,
+  type SpotlightPortraitLayoutMedia,
+} from "./layout-types.ts";
+import { ElementCallError, UnknownCallError } from "../utils/errors.ts";
+import { ObservableScope } from "./ObservableScope.ts";
 
 export interface CallViewModelOptions {
   encryptionSystem: EncryptionSystem;
@@ -161,287 +165,17 @@ const smallMobileCallThreshold = 3;
 // with the interface
 const showFooterMs = 4000;
 
-export interface GridLayoutMedia {
-  type: "grid";
-  spotlight?: MediaViewModel[];
-  grid: UserMediaViewModel[];
-}
-
-export interface SpotlightLandscapeLayoutMedia {
-  type: "spotlight-landscape";
-  spotlight: MediaViewModel[];
-  grid: UserMediaViewModel[];
-}
-
-export interface SpotlightPortraitLayoutMedia {
-  type: "spotlight-portrait";
-  spotlight: MediaViewModel[];
-  grid: UserMediaViewModel[];
-}
-
-export interface SpotlightExpandedLayoutMedia {
-  type: "spotlight-expanded";
-  spotlight: MediaViewModel[];
-  pip?: UserMediaViewModel;
-}
-
-export interface OneOnOneLayoutMedia {
-  type: "one-on-one";
-  local: UserMediaViewModel;
-  remote: UserMediaViewModel;
-}
-
-export interface PipLayoutMedia {
-  type: "pip";
-  spotlight: MediaViewModel[];
-}
-
-export type LayoutMedia =
-  | GridLayoutMedia
-  | SpotlightLandscapeLayoutMedia
-  | SpotlightPortraitLayoutMedia
-  | SpotlightExpandedLayoutMedia
-  | OneOnOneLayoutMedia
-  | PipLayoutMedia;
-
-export interface GridLayout {
-  type: "grid";
-  spotlight?: SpotlightTileViewModel;
-  grid: GridTileViewModel[];
-  setVisibleTiles: (value: number) => void;
-}
-
-export interface SpotlightLandscapeLayout {
-  type: "spotlight-landscape";
-  spotlight: SpotlightTileViewModel;
-  grid: GridTileViewModel[];
-  setVisibleTiles: (value: number) => void;
-}
-
-export interface SpotlightPortraitLayout {
-  type: "spotlight-portrait";
-  spotlight: SpotlightTileViewModel;
-  grid: GridTileViewModel[];
-  setVisibleTiles: (value: number) => void;
-}
-
-export interface SpotlightExpandedLayout {
-  type: "spotlight-expanded";
-  spotlight: SpotlightTileViewModel;
-  pip?: GridTileViewModel;
-}
-
-export interface OneOnOneLayout {
-  type: "one-on-one";
-  local: GridTileViewModel;
-  remote: GridTileViewModel;
-}
-
-export interface PipLayout {
-  type: "pip";
-  spotlight: SpotlightTileViewModel;
-}
-
-/**
- * A layout defining the media tiles present on screen and their visual
- * arrangement.
- */
-export type Layout =
-  | GridLayout
-  | SpotlightLandscapeLayout
-  | SpotlightPortraitLayout
-  | SpotlightExpandedLayout
-  | OneOnOneLayout
-  | PipLayout;
-
 export type GridMode = "grid" | "spotlight";
 
 export type WindowMode = "normal" | "narrow" | "flat" | "pip";
 
-/**
- * Sorting bins defining the order in which media tiles appear in the layout.
- */
-enum SortingBin {
-  /**
-   * Yourself, when the "always show self" option is on.
-   */
-  SelfAlwaysShown,
-  /**
-   * Participants that are sharing their screen.
-   */
-  Presenters,
-  /**
-   * Participants that have been speaking recently.
-   */
-  Speakers,
-  /**
-   * Participants that have their hand raised.
-   */
-  HandRaised,
-  /**
-   * Participants with video.
-   */
-  Video,
-  /**
-   * Participants not sharing any video.
-   */
-  NoVideo,
-  /**
-   * Yourself, when the "always show self" option is off.
-   */
-  SelfNotAlwaysShown,
-}
-
 interface LayoutScanState {
   layout: Layout | null;
   tiles: TileStore;
 }
 
-class UserMedia {
-  private readonly scope = new ObservableScope();
-  public readonly vm: UserMediaViewModel;
-  private readonly participant$: BehaviorSubject<
-    LocalParticipant | RemoteParticipant | undefined
-  >;
-
-  public readonly speaker$: Behavior<boolean>;
-  public readonly presenter$: Behavior<boolean>;
-  public constructor(
-    public readonly id: string,
-    member: RoomMember,
-    participant: LocalParticipant | RemoteParticipant | undefined,
-    encryptionSystem: EncryptionSystem,
-    livekitRoom: LivekitRoom,
-    mediaDevices: MediaDevices,
-    pretendToBeDisconnected$: Behavior<boolean>,
-    displayname$: Observable<string>,
-    handRaised$: Observable<Date | null>,
-    reaction$: Observable<ReactionOption | null>,
-  ) {
-    this.participant$ = new BehaviorSubject(participant);
-
-    if (participant?.isLocal) {
-      this.vm = new LocalUserMediaViewModel(
-        this.id,
-        member,
-        this.participant$ as Behavior<LocalParticipant>,
-        encryptionSystem,
-        livekitRoom,
-        mediaDevices,
-        this.scope.behavior(displayname$),
-        this.scope.behavior(handRaised$),
-        this.scope.behavior(reaction$),
-      );
-    } else {
-      this.vm = new RemoteUserMediaViewModel(
-        id,
-        member,
-        this.participant$.asObservable() as Observable<
-          RemoteParticipant | undefined
-        >,
-        encryptionSystem,
-        livekitRoom,
-        pretendToBeDisconnected$,
-        this.scope.behavior(displayname$),
-        this.scope.behavior(handRaised$),
-        this.scope.behavior(reaction$),
-      );
-    }
-
-    this.speaker$ = this.scope.behavior(observeSpeaker$(this.vm.speaking$));
-
-    this.presenter$ = this.scope.behavior(
-      this.participant$.pipe(
-        switchMap((p) => (p === undefined ? of(false) : sharingScreen$(p))),
-      ),
-    );
-  }
-
-  public updateParticipant(
-    newParticipant: LocalParticipant | RemoteParticipant | undefined,
-  ): void {
-    if (this.participant$.value !== newParticipant) {
-      // Update the BehaviourSubject in the UserMedia.
-      this.participant$.next(newParticipant);
-    }
-  }
-
-  public destroy(): void {
-    this.scope.end();
-    this.vm.destroy();
-  }
-}
-
-class ScreenShare {
-  private readonly scope = new ObservableScope();
-  public readonly vm: ScreenShareViewModel;
-  private readonly participant$: BehaviorSubject<
-    LocalParticipant | RemoteParticipant
-  >;
-
-  public constructor(
-    id: string,
-    member: RoomMember,
-    participant: LocalParticipant | RemoteParticipant,
-    encryptionSystem: EncryptionSystem,
-    livekitRoom: LivekitRoom,
-    pretendToBeDisconnected$: Behavior<boolean>,
-    displayName$: Observable<string>,
-  ) {
-    this.participant$ = new BehaviorSubject(participant);
-
-    this.vm = new ScreenShareViewModel(
-      id,
-      member,
-      this.participant$.asObservable(),
-      encryptionSystem,
-      livekitRoom,
-      pretendToBeDisconnected$,
-      this.scope.behavior(displayName$),
-      participant.isLocal,
-    );
-  }
-
-  public destroy(): void {
-    this.scope.end();
-    this.vm.destroy();
-  }
-}
-
 type MediaItem = UserMedia | ScreenShare;
 
-function getRoomMemberFromRtcMember(
-  rtcMember: CallMembership,
-  room: MatrixRoom,
-): { id: string; member: RoomMember | undefined } {
-  // WARN! This is not exactly the sender but the user defined in the state key.
-  // This will be available once we change to the new "member as object" format in the MatrixRTC object.
-  let id = rtcMember.sender + ":" + rtcMember.deviceId;
-
-  if (!rtcMember.sender) {
-    return { id, member: undefined };
-  }
-  if (
-    rtcMember.sender === room.client.getUserId() &&
-    rtcMember.deviceId === room.client.getDeviceId()
-  ) {
-    id = "local";
-  }
-
-  const member = room.getMember(rtcMember.sender) ?? undefined;
-  return { id, member };
-}
-
-function sharingScreen$(p: Participant): Observable<boolean> {
-  return observeParticipantEvents(
-    p,
-    ParticipantEvent.TrackPublished,
-    ParticipantEvent.TrackUnpublished,
-    ParticipantEvent.LocalTrackPublished,
-    ParticipantEvent.LocalTrackUnpublished,
-  ).pipe(map((p) => p.isScreenShareEnabled));
-}
-
 export class CallViewModel extends ViewModel {
   private readonly urlParams = getUrlParams();
 
@@ -459,6 +193,19 @@ export class CallViewModel extends ViewModel {
         }
       : undefined;
 
+  private readonly _configError$ = new BehaviorSubject<ElementCallError | null>(
+    null,
+  );
+
+  /**
+   * If there is a configuration error with the call (e.g. misconfigured E2EE).
+   * This is a fatal error that prevents the call from being created/joined.
+   * Should render a blocking error screen.
+   */
+  public get configError$(): Behavior<ElementCallError | null> {
+    return this._configError$;
+  }
+
   private readonly join$ = new Subject<void>();
 
   public join(): void {
@@ -508,30 +255,34 @@ export class CallViewModel extends ViewModel {
    * The transport that we would personally prefer to publish on (if not for the
    * transport preferences of others, perhaps).
    */
-  private readonly preferredTransport = makeTransport(this.matrixRTCSession);
+  private readonly preferredTransport$ = this.scope.behavior(
+    async$(makeTransport(this.matrixRTCSession)),
+  );
 
   /**
    * Lists the transports used by ourselves, plus all other MatrixRTC session
-   * members.
+   * members. For completeness this also lists the preferred transport and
+   * whether we are in multi-SFU mode (because advertisedTransport$ wants to
+   * read them at the same time, and bundling data together when it might change
+   * together is what you have to do in RxJS to avoid reading inconsistent state
+   * or observing too many changes.)
    */
   private readonly transports$: Behavior<{
     local: Async<LivekitTransport>;
     remote: { membership: CallMembership; transport: LivekitTransport }[];
+    preferred: Async<LivekitTransport>;
+    multiSfu: boolean;
   } | null> = this.scope.behavior(
     this.joined$.pipe(
       switchMap((joined) =>
         joined
           ? combineLatest(
-              [
-                async$(this.preferredTransport),
-                this.memberships$,
-                multiSfu.value$,
-              ],
+              [this.preferredTransport$, this.memberships$, multiSfu.value$],
               (preferred, memberships, multiSfu) => {
                 const oldestMembership =
                   this.matrixRTCSession.getOldestMembership();
                 const remote = memberships.flatMap((m) => {
-                  if (m.sender === this.userId && m.deviceId === this.deviceId)
+                  if (m.userId === this.userId && m.deviceId === this.deviceId)
                     return [];
                   const t = m.getTransport(oldestMembership ?? m);
                   return t && isLivekitTransport(t)
@@ -548,7 +299,14 @@ export class CallViewModel extends ViewModel {
                       local = ready(selection);
                   }
                 }
-                return { local, remote };
+                if (local.state === "error") {
+                  this._configError$.next(
+                    local.value instanceof ElementCallError
+                      ? local.value
+                      : new UnknownCallError(local.value),
+                  );
+                }
+                return { local, remote, preferred, multiSfu };
               },
             )
           : of(null),
@@ -576,6 +334,35 @@ export class CallViewModel extends ViewModel {
       ),
     );
 
+  /**
+   * The transport we should advertise in our MatrixRTC membership (plus whether
+   * it is a multi-SFU transport).
+   */
+  private readonly advertisedTransport$: Behavior<{
+    multiSfu: boolean;
+    transport: LivekitTransport;
+  } | null> = this.scope.behavior(
+    this.transports$.pipe(
+      map((transports) =>
+        transports?.local.state === "ready" &&
+        transports.preferred.state === "ready"
+          ? {
+              multiSfu: transports.multiSfu,
+              // In non-multi-SFU mode we should always advertise the preferred
+              // SFU to minimize the number of membership updates
+              transport: transports.multiSfu
+                ? transports.local.value
+                : transports.preferred.value,
+            }
+          : null,
+      ),
+      distinctUntilChanged<{
+        multiSfu: boolean;
+        transport: LivekitTransport;
+      } | null>(deepCompare),
+    ),
+  );
+
   /**
    * The local connection over which we will publish our media. It could
    * possibly also have some remote users' media available on it.
@@ -606,22 +393,23 @@ export class CallViewModel extends ViewModel {
       ),
     );
 
-  public readonly livekitConnectionState$ = this.scope.behavior(
-    this.localConnection$.pipe(
-      switchMap((c) =>
-        c?.state === "ready"
-          ? // TODO mapping to ConnectionState for compatibility, but we should use the full state?
-            c.value.focusConnectionState$.pipe(
-              map((s) => {
-                if (s.state === "ConnectedToLkRoom") return s.connectionState;
-                return ConnectionState.Disconnected;
-              }),
-              distinctUntilChanged(),
-            )
-          : of(ConnectionState.Disconnected),
+  public readonly livekitConnectionState$ =
+    this.scope.behavior<ConnectionState>(
+      this.localConnection$.pipe(
+        switchMap((c) =>
+          c?.state === "ready"
+            ? // TODO mapping to ConnectionState for compatibility, but we should use the full state?
+              c.value.transportState$.pipe(
+                switchMap((s) => {
+                  if (s.state === "ConnectedToLkRoom")
+                    return s.connectionState$;
+                  return of(ConnectionState.Disconnected);
+                }),
+              )
+            : of(ConnectionState.Disconnected),
+        ),
       ),
-    ),
-  );
+    );
 
   /**
    * Connections for each transport in use by one or more session members that
@@ -719,7 +507,7 @@ export class CallViewModel extends ViewModel {
       map((connections) =>
         [...connections.values()].map((c) => ({
           room: c.livekitRoom,
-          url: c.localTransport.livekit_service_url,
+          url: c.transport.livekit_service_url,
           isLocal: c instanceof PublishConnection,
         })),
       ),
@@ -729,6 +517,9 @@ export class CallViewModel extends ViewModel {
   private readonly userId = this.matrixRoom.client.getUserId()!;
   private readonly deviceId = this.matrixRoom.client.getDeviceId()!;
 
+  /**
+   * Whether we are connected to the MatrixRTC session.
+   */
   private readonly matrixConnected$ = this.scope.behavior(
     // To consider ourselves connected to MatrixRTC, we check the following:
     and$(
@@ -763,6 +554,10 @@ export class CallViewModel extends ViewModel {
     ),
   );
 
+  /**
+   * Whether we are "fully" connected to the call. Accounts for both the
+   * connection to the MatrixRTC session and the LiveKit publish connection.
+   */
   private readonly connected$ = this.scope.behavior(
     and$(
       this.matrixConnected$,
@@ -780,7 +575,7 @@ export class CallViewModel extends ViewModel {
       // We are reconnecting if we previously had some successful initial
       // connection but are now disconnected
       scan(
-        ({ connectedPreviously, reconnecting }, connectedNow) => ({
+        ({ connectedPreviously }, connectedNow) => ({
           connectedPreviously: connectedPreviously || connectedNow,
           reconnecting: connectedPreviously && !connectedNow,
         }),
@@ -807,7 +602,7 @@ export class CallViewModel extends ViewModel {
   private readonly participantsByRoom$ = this.scope.behavior<
     {
       livekitRoom: LivekitRoom;
-      url: string;
+      url: string; // Included for use as a React key
       participants: {
         id: string;
         participant: LocalParticipant | RemoteParticipant | undefined;
@@ -844,7 +639,7 @@ export class CallViewModel extends ViewModel {
                           | undefined;
                         member: RoomMember;
                       }[] = ps.map(({ participant, membership }) => ({
-                        id: `${membership.sender}:${membership.deviceId}`,
+                        id: `${membership.userId}:${membership.deviceId}`,
                         participant,
                         member:
                           getRoomMemberFromRtcMember(
@@ -857,7 +652,7 @@ export class CallViewModel extends ViewModel {
 
                       return {
                         livekitRoom: c.livekitRoom,
-                        url: c.localTransport.livekit_service_url,
+                        url: c.transport.livekit_service_url,
                         participants,
                       };
                     }),
@@ -921,7 +716,7 @@ export class CallViewModel extends ViewModel {
 
         // We only consider RTC members for disambiguation as they are the only visible members.
         for (const rtcMember of memberships) {
-          const matrixIdentifier = `${rtcMember.sender}:${rtcMember.deviceId}`;
+          const matrixIdentifier = `${rtcMember.userId}:${rtcMember.deviceId}`;
           const { member } = getRoomMemberFromRtcMember(rtcMember, room);
           if (!member) {
             logger.error(
@@ -967,7 +762,11 @@ export class CallViewModel extends ViewModel {
       scan((prevItems, [participantsByRoom, duplicateTiles]) => {
         const newItems: Map<string, UserMedia | ScreenShare> = new Map(
           function* (this: CallViewModel): Iterable<[string, MediaItem]> {
-            for (const { livekitRoom, participants } of participantsByRoom) {
+            for (const {
+              livekitRoom,
+              participants,
+              url,
+            } of participantsByRoom) {
               for (const { id, participant, member } of participants) {
                 for (let i = 0; i < 1 + duplicateTiles; i++) {
                   const mediaId = `${id}:${i}`;
@@ -987,6 +786,7 @@ export class CallViewModel extends ViewModel {
                         participant,
                         this.options.encryptionSystem,
                         livekitRoom,
+                        url,
                         this.mediaDevices,
                         this.pretendToBeDisconnected$,
                         this.memberDisplaynames$.pipe(
@@ -1008,6 +808,7 @@ export class CallViewModel extends ViewModel {
                           participant,
                           this.options.encryptionSystem,
                           livekitRoom,
+                          url,
                           this.pretendToBeDisconnected$,
                           this.memberDisplaynames$.pipe(
                             map((m) => m.get(id) ?? "[👻]"),
@@ -1068,8 +869,8 @@ export class CallViewModel extends ViewModel {
     pairwise(),
     filter(
       ([prev, current]) =>
-        current.every((m) => m.sender === this.userId) &&
-        prev.some((m) => m.sender !== this.userId),
+        current.every((m) => m.userId === this.userId) &&
+        prev.some((m) => m.userId !== this.userId),
     ),
     map(() => {}),
   );
@@ -1144,7 +945,7 @@ export class CallViewModel extends ViewModel {
    * Whether some Matrix user other than ourself is joined to the call.
    */
   private readonly someoneElseJoined$ = this.memberships$.pipe(
-    map((ms) => ms.some((m) => m.sender !== this.userId)),
+    map((ms) => ms.some((m) => m.userId !== this.userId)),
   ) as Behavior<boolean>;
 
   /**
@@ -1288,31 +1089,7 @@ export class CallViewModel extends ViewModel {
     this.userMedia$.pipe(
       switchMap((mediaItems) => {
         const bins = mediaItems.map((m) =>
-          combineLatest(
-            [
-              m.speaker$,
-              m.presenter$,
-              m.vm.videoEnabled$,
-              m.vm.handRaised$,
-              m.vm instanceof LocalUserMediaViewModel
-                ? m.vm.alwaysShow$
-                : of(false),
-            ],
-            (speaker, presenter, video, handRaised, alwaysShow) => {
-              let bin: SortingBin;
-              if (m.vm.local)
-                bin = alwaysShow
-                  ? SortingBin.SelfAlwaysShown
-                  : SortingBin.SelfNotAlwaysShown;
-              else if (presenter) bin = SortingBin.Presenters;
-              else if (speaker) bin = SortingBin.Speakers;
-              else if (handRaised) bin = SortingBin.HandRaised;
-              else if (video) bin = SortingBin.Video;
-              else bin = SortingBin.NoVideo;
-
-              return [m, bin] as const;
-            },
-          ),
+          m.bin$.pipe(map((bin) => [m, bin] as const)),
         );
         // Sort the media by bin order and generate a tile for each one
         return bins.length === 0
@@ -1983,13 +1760,11 @@ export class CallViewModel extends ViewModel {
       .pipe(this.scope.bind())
       .subscribe(({ start, stop }) => {
         for (const c of stop) {
-          logger.info(
-            `Disconnecting from ${c.localTransport.livekit_service_url}`,
-          );
+          logger.info(`Disconnecting from ${c.transport.livekit_service_url}`);
           c.stop().catch((err) => {
             // TODO: better error handling
             logger.error(
-              `Fail to stop connection to ${c.localTransport.livekit_service_url}`,
+              `Fail to stop connection to ${c.transport.livekit_service_url}`,
               err,
             );
           });
@@ -1997,45 +1772,53 @@ export class CallViewModel extends ViewModel {
         for (const c of start) {
           c.start().then(
             () =>
-              logger.info(
-                `Connected to ${c.localTransport.livekit_service_url}`,
-              ),
-            (e) =>
+              logger.info(`Connected to ${c.transport.livekit_service_url}`),
+            (e) => {
+              // We only want to report fatal errors `_configError$` for the publish connection.
+              // If there is an error with another connection, it will not terminate the call and will be displayed
+              // on eacn tile.
+              if (
+                c instanceof PublishConnection &&
+                e instanceof ElementCallError
+              ) {
+                this._configError$.next(e);
+              }
               logger.error(
-                `Failed to start connection to ${c.localTransport.livekit_service_url}`,
+                `Failed to start connection to ${c.transport.livekit_service_url}`,
                 e,
-              ),
+              );
+            },
           );
         }
       });
 
     // Start and stop session membership as needed
-    this.scope.reconcile(this.localTransport$, async (localTransport) => {
-      if (localTransport?.state === "ready") {
+    this.scope.reconcile(this.advertisedTransport$, async (advertised) => {
+      if (advertised !== null) {
         try {
-          await enterRTCSession(
-            this.matrixRTCSession,
-            localTransport.value,
-            this.options.encryptionSystem.kind !== E2eeType.NONE,
-            true,
-            true,
-            multiSfu.value$.value,
-          );
+          this._configError$.next(null);
+          await enterRTCSession(this.matrixRTCSession, advertised.transport, {
+            encryptMedia: this.options.encryptionSystem.kind !== E2eeType.NONE,
+            useExperimentalToDeviceTransport: true,
+            useNewMembershipManager: true,
+            useMultiSfu: advertised.multiSfu,
+          });
         } catch (e) {
           logger.error("Error entering RTC session", e);
         }
+
         // Update our member event when our mute state changes.
-        const muteSubscription = this.muteStates.video.enabled$.subscribe(
-          (videoEnabled) =>
-            // TODO: Ensure that these calls are serialized in case of
-            // fast video toggling
-            void this.matrixRTCSession.updateCallIntent(
+        const intentScope = new ObservableScope();
+        intentScope.reconcile(
+          this.muteStates.video.enabled$,
+          async (videoEnabled) =>
+            this.matrixRTCSession.updateCallIntent(
               videoEnabled ? "video" : "audio",
             ),
         );
 
         return async (): Promise<void> => {
-          muteSubscription.unsubscribe();
+          intentScope.end();
           // Only sends Matrix leave event. The LiveKit session will disconnect
           // as soon as either the stopConnection$ handler above gets to it or
           // the view model is destroyed.
@@ -2131,3 +1914,23 @@ function getE2eeKeyProvider(
     return keyProvider;
   }
 }
+
+function getRoomMemberFromRtcMember(
+  rtcMember: CallMembership,
+  room: MatrixRoom,
+): { id: string; member: RoomMember | undefined } {
+  let id = rtcMember.userId + ":" + rtcMember.deviceId;
+
+  if (!rtcMember.userId) {
+    return { id, member: undefined };
+  }
+  if (
+    rtcMember.userId === room.client.getUserId() &&
+    rtcMember.deviceId === room.client.getDeviceId()
+  ) {
+    id = "local";
+  }
+
+  const member = room.getMember(rtcMember.userId) ?? undefined;
+  return { id, member };
+}
diff --git a/src/state/Connection.test.ts b/src/state/Connection.test.ts
index 14c42206..b5389db4 100644
--- a/src/state/Connection.test.ts
+++ b/src/state/Connection.test.ts
@@ -34,7 +34,8 @@ import type {
 } from "matrix-js-sdk/lib/matrixrtc";
 import {
   type ConnectionOpts,
-  type FocusConnectionState,
+  type TransportState,
+  type PublishingParticipant,
   RemoteConnection,
 } from "./Connection.ts";
 import { ObservableScope } from "./ObservableScope.ts";
@@ -160,9 +161,7 @@ describe("Start connection states", () => {
     };
     const connection = new RemoteConnection(opts, undefined);
 
-    expect(connection.focusConnectionState$.getValue().state).toEqual(
-      "Initialized",
-    );
+    expect(connection.transportState$.getValue().state).toEqual("Initialized");
   });
 
   it("fail to getOpenId token then error state", async () => {
@@ -179,8 +178,8 @@ describe("Start connection states", () => {
 
     const connection = new RemoteConnection(opts, undefined);
 
-    const capturedStates: FocusConnectionState[] = [];
-    const s = connection.focusConnectionState$.subscribe((value) => {
+    const capturedStates: TransportState[] = [];
+    const s = connection.transportState$.subscribe((value) => {
       capturedStates.push(value);
     });
     onTestFinished(() => s.unsubscribe());
@@ -208,7 +207,7 @@ describe("Start connection states", () => {
     capturedState = capturedStates.pop();
     if (capturedState!.state === "FailedToStart") {
       expect(capturedState!.error.message).toEqual("Something went wrong");
-      expect(capturedState!.focus.livekit_alias).toEqual(
+      expect(capturedState!.transport.livekit_alias).toEqual(
         livekitFocus.livekit_alias,
       );
     } else {
@@ -232,8 +231,8 @@ describe("Start connection states", () => {
 
     const connection = new RemoteConnection(opts, undefined);
 
-    const capturedStates: FocusConnectionState[] = [];
-    const s = connection.focusConnectionState$.subscribe((value) => {
+    const capturedStates: TransportState[] = [];
+    const s = connection.transportState$.subscribe((value) => {
       capturedStates.push(value);
     });
     onTestFinished(() => s.unsubscribe());
@@ -265,7 +264,7 @@ describe("Start connection states", () => {
       expect(capturedState?.error.message).toContain(
         "SFU Config fetch failed with exception Error",
       );
-      expect(capturedState?.focus.livekit_alias).toEqual(
+      expect(capturedState?.transport.livekit_alias).toEqual(
         livekitFocus.livekit_alias,
       );
     } else {
@@ -289,8 +288,8 @@ describe("Start connection states", () => {
 
     const connection = new RemoteConnection(opts, undefined);
 
-    const capturedStates: FocusConnectionState[] = [];
-    const s = connection.focusConnectionState$.subscribe((value) => {
+    const capturedStates: TransportState[] = [];
+    const s = connection.transportState$.subscribe((value) => {
       capturedStates.push(value);
     });
     onTestFinished(() => s.unsubscribe());
@@ -330,7 +329,7 @@ describe("Start connection states", () => {
       expect(capturedState.error.message).toContain(
         "Failed to connect to livekit",
       );
-      expect(capturedState.focus.livekit_alias).toEqual(
+      expect(capturedState.transport.livekit_alias).toEqual(
         livekitFocus.livekit_alias,
       );
     } else {
@@ -346,8 +345,8 @@ describe("Start connection states", () => {
 
     const connection = setupRemoteConnection();
 
-    const capturedStates: FocusConnectionState[] = [];
-    const s = connection.focusConnectionState$.subscribe((value) => {
+    const capturedStates: TransportState[] = [];
+    const s = connection.transportState$.subscribe((value) => {
       capturedStates.push(value);
     });
     onTestFinished(() => s.unsubscribe());
@@ -365,59 +364,6 @@ describe("Start connection states", () => {
     expect(connectedState?.state).toEqual("ConnectedToLkRoom");
   });
 
-  it("should relay livekit events once connected", async () => {
-    setupTest();
-
-    const connection = setupRemoteConnection();
-
-    await connection.start();
-
-    let capturedStates: FocusConnectionState[] = [];
-    const s = connection.focusConnectionState$.subscribe((value) => {
-      capturedStates.push(value);
-    });
-    onTestFinished(() => s.unsubscribe());
-
-    const states = [
-      ConnectionState.Disconnected,
-      ConnectionState.Connecting,
-      ConnectionState.Connected,
-      ConnectionState.SignalReconnecting,
-      ConnectionState.Connecting,
-      ConnectionState.Connected,
-      ConnectionState.Reconnecting,
-    ];
-    for (const state of states) {
-      fakeRoomEventEmiter.emit(RoomEvent.ConnectionStateChanged, state);
-    }
-
-    for (const state of states) {
-      const s = capturedStates.shift();
-      expect(s?.state).toEqual("ConnectedToLkRoom");
-      const connectedState = s as FocusConnectionState & {
-        state: "ConnectedToLkRoom";
-      };
-      expect(connectedState.connectionState).toEqual(state);
-
-      // should always have the focus info
-      expect(connectedState.focus.livekit_alias).toEqual(
-        livekitFocus.livekit_alias,
-      );
-      expect(connectedState.focus.livekit_service_url).toEqual(
-        livekitFocus.livekit_service_url,
-      );
-    }
-
-    // If the state is not ConnectedToLkRoom, no events should be relayed anymore
-    await connection.stop();
-    capturedStates = [];
-    for (const state of states) {
-      fakeRoomEventEmiter.emit(RoomEvent.ConnectionStateChanged, state);
-    }
-
-    expect(capturedStates.length).toEqual(0);
-  });
-
   it("shutting down the scope should stop the connection", async () => {
     setupTest();
     vi.useFakeTimers();
@@ -434,16 +380,16 @@ describe("Start connection states", () => {
 });
 
 function fakeRemoteLivekitParticipant(id: string): RemoteParticipant {
-  return vi.mocked<RemoteParticipant>({
+  return {
     identity: id,
-  } as unknown as RemoteParticipant);
+  } as unknown as RemoteParticipant;
 }
 
 function fakeRtcMemberShip(userId: string, deviceId: string): CallMembership {
-  return vi.mocked<CallMembership>({
-    sender: userId,
-    deviceId: deviceId,
-  } as unknown as CallMembership);
+  return {
+    userId,
+    deviceId,
+  } as unknown as CallMembership;
 }
 
 describe("Publishing participants observations", () => {
@@ -454,22 +400,19 @@ describe("Publishing participants observations", () => {
 
     const bobIsAPublisher = Promise.withResolvers<void>();
     const danIsAPublisher = Promise.withResolvers<void>();
-    const observedPublishers: {
-      participant: RemoteParticipant;
-      membership: CallMembership;
-    }[][] = [];
+    const observedPublishers: PublishingParticipant[][] = [];
     const s = connection.publishingParticipants$.subscribe((publishers) => {
       observedPublishers.push(publishers);
       if (
         publishers.some(
-          (p) => p.participant.identity === "@bob:example.org:DEV111",
+          (p) => p.participant?.identity === "@bob:example.org:DEV111",
         )
       ) {
         bobIsAPublisher.resolve();
       }
       if (
         publishers.some(
-          (p) => p.participant.identity === "@dan:example.org:DEV333",
+          (p) => p.participant?.identity === "@dan:example.org:DEV333",
         )
       ) {
         danIsAPublisher.resolve();
@@ -529,7 +472,7 @@ describe("Publishing participants observations", () => {
     await bobIsAPublisher.promise;
     const publishers = observedPublishers.pop();
     expect(publishers?.length).toEqual(1);
-    expect(publishers?.[0].participant.identity).toEqual(
+    expect(publishers?.[0].participant?.identity).toEqual(
       "@bob:example.org:DEV111",
     );
 
@@ -546,12 +489,12 @@ describe("Publishing participants observations", () => {
     expect(twoPublishers?.length).toEqual(2);
     expect(
       twoPublishers?.some(
-        (p) => p.participant.identity === "@bob:example.org:DEV111",
+        (p) => p.participant?.identity === "@bob:example.org:DEV111",
       ),
     ).toBeTruthy();
     expect(
       twoPublishers?.some(
-        (p) => p.participant.identity === "@dan:example.org:DEV333",
+        (p) => p.participant?.identity === "@dan:example.org:DEV333",
       ),
     ).toBeTruthy();
 
@@ -568,12 +511,25 @@ describe("Publishing participants observations", () => {
     );
 
     const updatedPublishers = observedPublishers.pop();
-    expect(updatedPublishers?.length).toEqual(1);
+    // Bob is not connected to the room but he is still in the rtc memberships declaring that
+    // he is using that focus to publish, so he should still appear as a publisher
+    expect(updatedPublishers?.length).toEqual(2);
+    const pp = updatedPublishers?.find(
+      (p) => p.membership.userId == "@bob:example.org",
+    );
+    expect(pp).toBeDefined();
+    expect(pp!.participant).not.toBeDefined();
     expect(
       updatedPublishers?.some(
-        (p) => p.participant.identity === "@dan:example.org:DEV333",
+        (p) => p.participant?.identity === "@dan:example.org:DEV333",
       ),
     ).toBeTruthy();
+    // Now if bob is not in the rtc memberships, he should disappear
+    const noBob = rtcMemberships.filter(
+      ({ membership }) => membership.userId !== "@bob:example.org",
+    );
+    fakeMembershipsFocusMap$.next(noBob);
+    expect(observedPublishers.pop()?.length).toEqual(1);
   });
 
   it("should be scoped to parent scope", (): void => {
@@ -581,10 +537,7 @@ describe("Publishing participants observations", () => {
 
     const connection = setupRemoteConnection();
 
-    let observedPublishers: {
-      participant: RemoteParticipant;
-      membership: CallMembership;
-    }[][] = [];
+    let observedPublishers: PublishingParticipant[][] = [];
     const s = connection.publishingParticipants$.subscribe((publishers) => {
       observedPublishers.push(publishers);
     });
@@ -619,7 +572,7 @@ describe("Publishing participants observations", () => {
     // We should have bob has a publisher now
     const publishers = observedPublishers.pop();
     expect(publishers?.length).toEqual(1);
-    expect(publishers?.[0].participant.identity).toEqual(
+    expect(publishers?.[0].participant?.identity).toEqual(
       "@bob:example.org:DEV111",
     );
 
diff --git a/src/state/Connection.ts b/src/state/Connection.ts
index b7864677..7b044e1d 100644
--- a/src/state/Connection.ts
+++ b/src/state/Connection.ts
@@ -10,8 +10,10 @@ import {
   connectionStateObserver,
 } from "@livekit/components-core";
 import {
+  ConnectionError,
   type ConnectionState,
   type E2EEOptions,
+  type RemoteParticipant,
   Room as LivekitRoom,
   type RoomOptions,
 } from "livekit-client";
@@ -19,7 +21,7 @@ import {
   type CallMembership,
   type LivekitTransport,
 } from "matrix-js-sdk/lib/matrixrtc";
-import { BehaviorSubject, combineLatest } from "rxjs";
+import { BehaviorSubject, combineLatest, type Observable } from "rxjs";
 
 import {
   getSFUConfigWithOpenID,
@@ -29,15 +31,19 @@ import {
 import { type Behavior } from "./Behavior";
 import { type ObservableScope } from "./ObservableScope";
 import { defaultLiveKitOptions } from "../livekit/options";
+import {
+  InsufficientCapacityError,
+  SFURoomCreationRestrictedError,
+} from "../utils/errors.ts";
 
 export interface ConnectionOpts {
-  /** The focus server to connect to. */
+  /** The media transport to connect to. */
   transport: LivekitTransport;
   /** The Matrix client to use for OpenID and SFU config requests. */
   client: OpenIDClientParts;
   /** The observable scope to use for this connection. */
   scope: ObservableScope;
-  /** An observable of the current RTC call memberships and their associated focus. */
+  /** An observable of the current RTC call memberships and their associated transports. */
   remoteTransports$: Behavior<
     { membership: CallMembership; transport: LivekitTransport }[]
   >;
@@ -46,18 +52,33 @@ export interface ConnectionOpts {
   livekitRoomFactory?: (options?: RoomOptions) => LivekitRoom;
 }
 
-export type FocusConnectionState =
+export type TransportState =
   | { state: "Initialized" }
-  | { state: "FetchingConfig"; focus: LivekitTransport }
-  | { state: "ConnectingToLkRoom"; focus: LivekitTransport }
-  | { state: "PublishingTracks"; focus: LivekitTransport }
-  | { state: "FailedToStart"; error: Error; focus: LivekitTransport }
+  | { state: "FetchingConfig"; transport: LivekitTransport }
+  | { state: "ConnectingToLkRoom"; transport: LivekitTransport }
+  | { state: "PublishingTracks"; transport: LivekitTransport }
+  | { state: "FailedToStart"; error: Error; transport: LivekitTransport }
   | {
       state: "ConnectedToLkRoom";
-      connectionState: ConnectionState;
-      focus: LivekitTransport;
+      connectionState$: Observable<ConnectionState>;
+      transport: LivekitTransport;
     }
-  | { state: "Stopped"; focus: LivekitTransport };
+  | { state: "Stopped"; transport: LivekitTransport };
+
+/**
+ * Represents participant publishing or expected to publish on the connection.
+ * It is paired with its associated rtc membership.
+ */
+export type PublishingParticipant = {
+  /**
+   * The LiveKit participant publishing on this connection, or undefined if the participant is not currently (yet) connected to the livekit room.
+   */
+  participant: RemoteParticipant | undefined;
+  /**
+   * The rtc call membership associated with this participant.
+   */
+  membership: CallMembership;
+};
 
 /**
  * A connection to a Matrix RTC LiveKit backend.
@@ -66,14 +87,15 @@ export type FocusConnectionState =
  */
 export class Connection {
   // Private Behavior
-  private readonly _focusConnectionState$ =
-    new BehaviorSubject<FocusConnectionState>({ state: "Initialized" });
+  private readonly _transportState$ = new BehaviorSubject<TransportState>({
+    state: "Initialized",
+  });
 
   /**
-   * The current state of the connection to the focus server.
+   * The current state of the connection to the media transport.
    */
-  public readonly focusConnectionState$: Behavior<FocusConnectionState> =
-    this._focusConnectionState$;
+  public readonly transportState$: Behavior<TransportState> =
+    this._transportState$;
 
   /**
    * Whether the connection has been stopped.
@@ -88,37 +110,62 @@ export class Connection {
    * 1. Request an OpenId token `request_token` (allows matrix users to verify their identity with a third-party service.)
    * 2. Use this token to request the SFU config to the MatrixRtc authentication service.
    * 3. Connect to the configured LiveKit room.
+   *
+   * @throws {InsufficientCapacityError} if the LiveKit server indicates that it has insufficient capacity to accept the connection.
+   * @throws {SFURoomCreationRestrictedError} if the LiveKit server indicates that the room does not exist and cannot be created.
    */
   public async start(): Promise<void> {
     this.stopped = false;
     try {
-      this._focusConnectionState$.next({
+      this._transportState$.next({
         state: "FetchingConfig",
-        focus: this.localTransport,
+        transport: this.transport,
       });
-      // TODO could this be loaded earlier to save time?
       const { url, jwt } = await this.getSFUConfigWithOpenID();
       // If we were stopped while fetching the config, don't proceed to connect
       if (this.stopped) return;
 
-      this._focusConnectionState$.next({
+      this._transportState$.next({
         state: "ConnectingToLkRoom",
-        focus: this.localTransport,
+        transport: this.transport,
       });
-      await this.livekitRoom.connect(url, jwt);
+      try {
+        await this.livekitRoom.connect(url, jwt);
+      } catch (e) {
+        // LiveKit uses 503 to indicate that the server has hit its track limits.
+        // https://github.com/livekit/livekit/blob/fcb05e97c5a31812ecf0ca6f7efa57c485cea9fb/pkg/service/rtcservice.go#L171
+        // It also errors with a status code of 200 (yes, really) for room
+        // participant limits.
+        // LiveKit Cloud uses 429 for connection limits.
+        // Either way, all these errors can be explained as "insufficient capacity".
+        if (e instanceof ConnectionError) {
+          if (e.status === 503 || e.status === 200 || e.status === 429) {
+            throw new InsufficientCapacityError();
+          }
+          if (e.status === 404) {
+            // error msg is "Could not establish signal connection: requested room does not exist"
+            // The room does not exist. There are two different modes of operation for the SFU:
+            // - the room is created on the fly when connecting (livekit `auto_create` option)
+            // - Only authorized users can create rooms, so the room must exist before connecting (done by the auth jwt service)
+            // In the first case there will not be a 404, so we are in the second case.
+            throw new SFURoomCreationRestrictedError();
+          }
+        }
+        throw e;
+      }
       // If we were stopped while connecting, don't proceed to update state.
       if (this.stopped) return;
 
-      this._focusConnectionState$.next({
+      this._transportState$.next({
         state: "ConnectedToLkRoom",
-        focus: this.localTransport,
-        connectionState: this.livekitRoom.state,
+        transport: this.transport,
+        connectionState$: connectionStateObserver(this.livekitRoom),
       });
     } catch (error) {
-      this._focusConnectionState$.next({
+      this._transportState$.next({
         state: "FailedToStart",
         error: error instanceof Error ? error : new Error(`${error}`),
-        focus: this.localTransport,
+        transport: this.transport,
       });
       throw error;
     }
@@ -127,8 +174,8 @@ export class Connection {
   protected async getSFUConfigWithOpenID(): Promise<SFUConfig> {
     return await getSFUConfigWithOpenID(
       this.client,
-      this.localTransport.livekit_service_url,
-      this.localTransport.livekit_alias,
+      this.transport.livekit_service_url,
+      this.transport.livekit_alias,
     );
   }
   /**
@@ -140,9 +187,9 @@ export class Connection {
   public async stop(): Promise<void> {
     if (this.stopped) return;
     await this.livekitRoom.disconnect();
-    this._focusConnectionState$.next({
+    this._transportState$.next({
       state: "Stopped",
-      focus: this.localTransport,
+      transport: this.transport,
     });
     this.stopped = true;
   }
@@ -152,12 +199,12 @@ export class Connection {
    * This is derived from `participantsIncludingSubscribers$` and `remoteTransports$`.
    * It filters the participants to only those that are associated with a membership that claims to publish on this connection.
    */
-  public readonly publishingParticipants$;
+  public readonly publishingParticipants$: Behavior<PublishingParticipant[]>;
 
   /**
-   * The focus server to connect to.
+   * The media transport to connect to.
    */
-  public readonly localTransport: LivekitTransport;
+  public readonly transport: LivekitTransport;
 
   private readonly client: OpenIDClientParts;
   /**
@@ -173,7 +220,7 @@ export class Connection {
   ) {
     const { transport, client, scope, remoteTransports$ } = opts;
 
-    this.localTransport = transport;
+    this.transport = transport;
     this.client = client;
 
     const participantsIncludingSubscribers$ = scope.behavior(
@@ -189,35 +236,20 @@ export class Connection {
             // Find all members that claim to publish on this connection
             .flatMap(({ membership, transport }) =>
               transport.livekit_service_url ===
-              this.localTransport.livekit_service_url
+              this.transport.livekit_service_url
                 ? [membership]
                 : [],
             )
             // Pair with their associated LiveKit participant (if any)
-            // Uses flatMap to filter out memberships with no associated rtc participant ([])
-            .flatMap((membership) => {
-              const id = `${membership.sender}:${membership.deviceId}`;
+            .map((membership) => {
+              const id = `${membership.userId}:${membership.deviceId}`;
               const participant = participants.find((p) => p.identity === id);
-              return participant ? [{ participant, membership }] : [];
+              return { participant, membership };
             }),
       ),
       [],
     );
 
-    scope
-      .behavior<ConnectionState>(connectionStateObserver(this.livekitRoom))
-      .subscribe((connectionState) => {
-        const current = this._focusConnectionState$.value;
-        // Only update the state if we are already connected to the LiveKit room.
-        if (current.state === "ConnectedToLkRoom") {
-          this._focusConnectionState$.next({
-            state: "ConnectedToLkRoom",
-            connectionState,
-            focus: current.focus,
-          });
-        }
-      });
-
     scope.onEnd(() => void this.stop());
   }
 }
diff --git a/src/state/GridLikeLayout.ts b/src/state/GridLikeLayout.ts
index 0740f26c..0d130834 100644
--- a/src/state/GridLikeLayout.ts
+++ b/src/state/GridLikeLayout.ts
@@ -5,7 +5,7 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type Layout, type LayoutMedia } from "./CallViewModel";
+import { type Layout, type LayoutMedia } from "./layout-types.ts";
 import { type TileStore } from "./TileStore";
 
 export type GridLikeLayoutType =
diff --git a/src/state/MediaViewModel.ts b/src/state/MediaViewModel.ts
index 016c6a49..de09e24d 100644
--- a/src/state/MediaViewModel.ts
+++ b/src/state/MediaViewModel.ts
@@ -266,6 +266,7 @@ abstract class BaseMediaViewModel extends ViewModel {
     audioSource: AudioSource,
     videoSource: VideoSource,
     livekitRoom: LivekitRoom,
+    public readonly focusURL: string,
     public readonly displayName$: Behavior<string>,
   ) {
     super();
@@ -407,6 +408,7 @@ abstract class BaseUserMediaViewModel extends BaseMediaViewModel {
     participant$: Observable<LocalParticipant | RemoteParticipant | undefined>,
     encryptionSystem: EncryptionSystem,
     livekitRoom: LivekitRoom,
+    focusUrl: string,
     displayName$: Behavior<string>,
     public readonly handRaised$: Behavior<Date | null>,
     public readonly reaction$: Behavior<ReactionOption | null>,
@@ -419,6 +421,7 @@ abstract class BaseUserMediaViewModel extends BaseMediaViewModel {
       Track.Source.Microphone,
       Track.Source.Camera,
       livekitRoom,
+      focusUrl,
       displayName$,
     );
 
@@ -539,6 +542,7 @@ export class LocalUserMediaViewModel extends BaseUserMediaViewModel {
     participant$: Behavior<LocalParticipant | undefined>,
     encryptionSystem: EncryptionSystem,
     livekitRoom: LivekitRoom,
+    focusURL: string,
     private readonly mediaDevices: MediaDevices,
     displayName$: Behavior<string>,
     handRaised$: Behavior<Date | null>,
@@ -550,6 +554,7 @@ export class LocalUserMediaViewModel extends BaseUserMediaViewModel {
       participant$,
       encryptionSystem,
       livekitRoom,
+      focusURL,
       displayName$,
       handRaised$,
       reaction$,
@@ -645,6 +650,7 @@ export class RemoteUserMediaViewModel extends BaseUserMediaViewModel {
     participant$: Observable<RemoteParticipant | undefined>,
     encryptionSystem: EncryptionSystem,
     livekitRoom: LivekitRoom,
+    focusUrl: string,
     private readonly pretendToBeDisconnected$: Behavior<boolean>,
     displayname$: Behavior<string>,
     handRaised$: Behavior<Date | null>,
@@ -656,6 +662,7 @@ export class RemoteUserMediaViewModel extends BaseUserMediaViewModel {
       participant$,
       encryptionSystem,
       livekitRoom,
+      focusUrl,
       displayname$,
       handRaised$,
       reaction$,
@@ -740,6 +747,7 @@ export class ScreenShareViewModel extends BaseMediaViewModel {
     participant$: Observable<LocalParticipant | RemoteParticipant>,
     encryptionSystem: EncryptionSystem,
     livekitRoom: LivekitRoom,
+    focusUrl: string,
     private readonly pretendToBeDisconnected$: Behavior<boolean>,
     displayname$: Behavior<string>,
     public readonly local: boolean,
@@ -752,6 +760,7 @@ export class ScreenShareViewModel extends BaseMediaViewModel {
       Track.Source.ScreenShareAudio,
       Track.Source.ScreenShare,
       livekitRoom,
+      focusUrl,
       displayname$,
     );
   }
diff --git a/src/state/ObservableScope.ts b/src/state/ObservableScope.ts
index d6fd8e32..879445e6 100644
--- a/src/state/ObservableScope.ts
+++ b/src/state/ObservableScope.ts
@@ -114,11 +114,11 @@ export class ObservableScope {
    */
   public reconcile<T>(
     value$: Behavior<T>,
-    callback: (value: T) => Promise<(() => Promise<void>) | undefined>,
+    callback: (value: T) => Promise<(() => Promise<void>) | void>,
   ): void {
     let latestValue: T | typeof nothing = nothing;
     let reconciledValue: T | typeof nothing = nothing;
-    let cleanUp: (() => Promise<void>) | undefined = undefined;
+    let cleanUp: (() => Promise<void>) | void = undefined;
     value$
       .pipe(
         catchError(() => EMPTY), // Ignore errors
diff --git a/src/state/OneOnOneLayout.ts b/src/state/OneOnOneLayout.ts
index b8c7b8fb..10268945 100644
--- a/src/state/OneOnOneLayout.ts
+++ b/src/state/OneOnOneLayout.ts
@@ -5,7 +5,7 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type OneOnOneLayout, type OneOnOneLayoutMedia } from "./CallViewModel";
+import { type OneOnOneLayout, type OneOnOneLayoutMedia } from "./layout-types";
 import { type TileStore } from "./TileStore";
 
 /**
diff --git a/src/state/PipLayout.ts b/src/state/PipLayout.ts
index ab066410..56e9aeb2 100644
--- a/src/state/PipLayout.ts
+++ b/src/state/PipLayout.ts
@@ -5,7 +5,7 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type PipLayout, type PipLayoutMedia } from "./CallViewModel";
+import { type PipLayout, type PipLayoutMedia } from "./layout-types.ts";
 import { type TileStore } from "./TileStore";
 
 /**
diff --git a/src/state/PublishConnection.ts b/src/state/PublishConnection.ts
index 9a219483..1bb79211 100644
--- a/src/state/PublishConnection.ts
+++ b/src/state/PublishConnection.ts
@@ -40,6 +40,8 @@ import { type ObservableScope } from "./ObservableScope.ts";
  * This connection will publish the local user's audio and video tracks.
  */
 export class PublishConnection extends Connection {
+  private readonly scope: ObservableScope;
+
   /**
    * Creates a new PublishConnection.
    * @param args - The connection options. {@link ConnectionOpts}
@@ -75,11 +77,10 @@ export class PublishConnection extends Connection {
     });
 
     super(room, args);
+    this.scope = scope;
 
     // Setup track processor syncing (blur)
     this.observeTrackProcessors(scope, room, trackerProcessorState$);
-    // Observe mute state changes and update LiveKit microphone/camera states accordingly
-    this.observeMuteStates(scope);
     // Observe media device changes and update LiveKit active devices accordingly
     this.observeMediaDevices(scope, devices, controlledAudioDevices);
 
@@ -94,29 +95,53 @@ export class PublishConnection extends Connection {
    * 2. Use this token to request the SFU config to the MatrixRtc authentication service.
    * 3. Connect to the configured LiveKit room.
    * 4. Create local audio and video tracks based on the current mute states and publish them to the room.
+   *
+   * @throws {InsufficientCapacityError} if the LiveKit server indicates that it has insufficient capacity to accept the connection.
+   * @throws {SFURoomCreationRestrictedError} if the LiveKit server indicates that the room does not exist and cannot be created.
    */
   public async start(): Promise<void> {
     this.stopped = false;
 
+    // Observe mute state changes and update LiveKit microphone/camera states accordingly
+    this.observeMuteStates(this.scope);
+
+    // TODO: This will fetch the JWT token. Perhaps we could keep it preloaded
+    // instead? This optimization would only be safe for a publish connection,
+    // because we don't want to leak the user's intent to perhaps join a call to
+    // remote servers before they actually commit to it.
     await super.start();
 
     if (this.stopped) return;
 
-    // TODO this can throw errors? It will also prompt for permissions if not already granted
-    const tracks = await this.livekitRoom.localParticipant.createTracks({
-      audio: this.muteStates.audio.enabled$.value,
-      video: this.muteStates.video.enabled$.value,
-    });
-    if (this.stopped) return;
-    for (const track of tracks) {
-      // TODO: handle errors? Needs the signaling connection to be up, but it has some retries internally
-      // with a timeout.
-      await this.livekitRoom.localParticipant.publishTrack(track);
+    // TODO-MULTI-SFU: Prepublish a microphone track
+    const audio = this.muteStates.audio.enabled$.value;
+    const video = this.muteStates.video.enabled$.value;
+    // createTracks throws if called with audio=false and video=false
+    if (audio || video) {
+      // TODO this can still throw errors? It will also prompt for permissions if not already granted
+      const tracks = await this.livekitRoom.localParticipant.createTracks({
+        audio,
+        video,
+      });
       if (this.stopped) return;
-      // TODO: check if the connection is still active? and break the loop if not?
+      for (const track of tracks) {
+        // TODO: handle errors? Needs the signaling connection to be up, but it has some retries internally
+        // with a timeout.
+        await this.livekitRoom.localParticipant.publishTrack(track);
+        if (this.stopped) return;
+        // TODO: check if the connection is still active? and break the loop if not?
+      }
     }
   }
 
+  public async stop(): Promise<void> {
+    // TODO-MULTI-SFU: Move these calls back to ObservableScope.onEnd once scope
+    // actually has the right lifetime
+    this.muteStates.audio.unsetHandler();
+    this.muteStates.video.unsetHandler();
+    await super.stop();
+  }
+
   /// Private methods
 
   // Restart the audio input track whenever we detect that the active media
@@ -223,10 +248,6 @@ export class PublishConnection extends Connection {
       }
       return this.livekitRoom.localParticipant.isCameraEnabled;
     });
-    scope.onEnd(() => {
-      this.muteStates.audio.unsetHandler();
-      this.muteStates.video.unsetHandler();
-    });
   }
 
   private observeTrackProcessors(
diff --git a/src/state/ScreenShare.ts b/src/state/ScreenShare.ts
new file mode 100644
index 00000000..e6fa81ec
--- /dev/null
+++ b/src/state/ScreenShare.ts
@@ -0,0 +1,56 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+import { of, type Observable } from "rxjs";
+import {
+  type LocalParticipant,
+  type RemoteParticipant,
+  type Room as LivekitRoom,
+} from "livekit-client";
+
+import { ObservableScope } from "./ObservableScope.ts";
+import { ScreenShareViewModel } from "./MediaViewModel.ts";
+import type { RoomMember } from "matrix-js-sdk";
+import type { EncryptionSystem } from "../e2ee/sharedKeyManagement.ts";
+import type { Behavior } from "./Behavior.ts";
+
+/**
+ * A screen share media item to be presented in a tile. This is a thin wrapper
+ * around ScreenShareViewModel which essentially just establishes an
+ * ObservableScope for behaviors that the view model depends on.
+ */
+export class ScreenShare {
+  private readonly scope = new ObservableScope();
+  public readonly vm: ScreenShareViewModel;
+
+  public constructor(
+    id: string,
+    member: RoomMember,
+    participant: LocalParticipant | RemoteParticipant,
+    encryptionSystem: EncryptionSystem,
+    livekitRoom: LivekitRoom,
+    focusUrl: string,
+    pretendToBeDisconnected$: Behavior<boolean>,
+    displayName$: Observable<string>,
+  ) {
+    this.vm = new ScreenShareViewModel(
+      id,
+      member,
+      of(participant),
+      encryptionSystem,
+      livekitRoom,
+      focusUrl,
+      pretendToBeDisconnected$,
+      this.scope.behavior(displayName$),
+      participant.isLocal,
+    );
+  }
+
+  public destroy(): void {
+    this.scope.end();
+    this.vm.destroy();
+  }
+}
diff --git a/src/state/SpotlightExpandedLayout.ts b/src/state/SpotlightExpandedLayout.ts
index 4baba0a1..8ccc49dd 100644
--- a/src/state/SpotlightExpandedLayout.ts
+++ b/src/state/SpotlightExpandedLayout.ts
@@ -8,7 +8,7 @@ Please see LICENSE in the repository root for full details.
 import {
   type SpotlightExpandedLayout,
   type SpotlightExpandedLayoutMedia,
-} from "./CallViewModel";
+} from "./layout-types";
 import { type TileStore } from "./TileStore";
 
 /**
diff --git a/src/state/UserMedia.ts b/src/state/UserMedia.ts
new file mode 100644
index 00000000..42016f7c
--- /dev/null
+++ b/src/state/UserMedia.ts
@@ -0,0 +1,186 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import {
+  BehaviorSubject,
+  combineLatest,
+  map,
+  type Observable,
+  of,
+  switchMap,
+} from "rxjs";
+import {
+  type LocalParticipant,
+  type Participant,
+  ParticipantEvent,
+  type RemoteParticipant,
+  type Room as LivekitRoom,
+} from "livekit-client";
+import { observeParticipantEvents } from "@livekit/components-core";
+
+import { ObservableScope } from "./ObservableScope.ts";
+import {
+  LocalUserMediaViewModel,
+  RemoteUserMediaViewModel,
+  type UserMediaViewModel,
+} from "./MediaViewModel.ts";
+import type { Behavior } from "./Behavior.ts";
+import type { RoomMember } from "matrix-js-sdk";
+import type { EncryptionSystem } from "../e2ee/sharedKeyManagement.ts";
+import type { MediaDevices } from "./MediaDevices.ts";
+import type { ReactionOption } from "../reactions";
+import { observeSpeaker$ } from "./observeSpeaker.ts";
+
+/**
+ * Sorting bins defining the order in which media tiles appear in the layout.
+ */
+enum SortingBin {
+  /**
+   * Yourself, when the "always show self" option is on.
+   */
+  SelfAlwaysShown,
+  /**
+   * Participants that are sharing their screen.
+   */
+  Presenters,
+  /**
+   * Participants that have been speaking recently.
+   */
+  Speakers,
+  /**
+   * Participants that have their hand raised.
+   */
+  HandRaised,
+  /**
+   * Participants with video.
+   */
+  Video,
+  /**
+   * Participants not sharing any video.
+   */
+  NoVideo,
+  /**
+   * Yourself, when the "always show self" option is off.
+   */
+  SelfNotAlwaysShown,
+}
+
+/**
+ * A user media item to be presented in a tile. This is a thin wrapper around
+ * UserMediaViewModel which additionally determines the media item's sorting bin
+ * for inclusion in the call layout.
+ */
+export class UserMedia {
+  private readonly scope = new ObservableScope();
+  private readonly participant$ = new BehaviorSubject(this.initialParticipant);
+
+  public readonly vm: UserMediaViewModel = this.participant$.value?.isLocal
+    ? new LocalUserMediaViewModel(
+        this.id,
+        this.member,
+        this.participant$ as Behavior<LocalParticipant>,
+        this.encryptionSystem,
+        this.livekitRoom,
+        this.focusURL,
+        this.mediaDevices,
+        this.scope.behavior(this.displayname$),
+        this.scope.behavior(this.handRaised$),
+        this.scope.behavior(this.reaction$),
+      )
+    : new RemoteUserMediaViewModel(
+        this.id,
+        this.member,
+        this.participant$ as Observable<RemoteParticipant | undefined>,
+        this.encryptionSystem,
+        this.livekitRoom,
+        this.focusURL,
+        this.pretendToBeDisconnected$,
+        this.scope.behavior(this.displayname$),
+        this.scope.behavior(this.handRaised$),
+        this.scope.behavior(this.reaction$),
+      );
+
+  private readonly speaker$ = this.scope.behavior(
+    observeSpeaker$(this.vm.speaking$),
+  );
+
+  private readonly presenter$ = this.scope.behavior(
+    this.participant$.pipe(
+      switchMap((p) => (p === undefined ? of(false) : sharingScreen$(p))),
+    ),
+  );
+
+  /**
+   * Which sorting bin the media item should be placed in.
+   */
+  // This is exposed here rather than by UserMediaViewModel because it's only
+  // relevant to the layout algorithms; the MediaView component should be
+  // ignorant of this value.
+  public readonly bin$ = combineLatest(
+    [
+      this.speaker$,
+      this.presenter$,
+      this.vm.videoEnabled$,
+      this.vm.handRaised$,
+      this.vm instanceof LocalUserMediaViewModel
+        ? this.vm.alwaysShow$
+        : of(false),
+    ],
+    (speaker, presenter, video, handRaised, alwaysShow) => {
+      if (this.vm.local)
+        return alwaysShow
+          ? SortingBin.SelfAlwaysShown
+          : SortingBin.SelfNotAlwaysShown;
+      else if (presenter) return SortingBin.Presenters;
+      else if (speaker) return SortingBin.Speakers;
+      else if (handRaised) return SortingBin.HandRaised;
+      else if (video) return SortingBin.Video;
+      else return SortingBin.NoVideo;
+    },
+  );
+
+  public constructor(
+    public readonly id: string,
+    private readonly member: RoomMember,
+    private readonly initialParticipant:
+      | LocalParticipant
+      | RemoteParticipant
+      | undefined,
+    private readonly encryptionSystem: EncryptionSystem,
+    private readonly livekitRoom: LivekitRoom,
+    private readonly focusURL: string,
+    private readonly mediaDevices: MediaDevices,
+    private readonly pretendToBeDisconnected$: Behavior<boolean>,
+    private readonly displayname$: Observable<string>,
+    private readonly handRaised$: Observable<Date | null>,
+    private readonly reaction$: Observable<ReactionOption | null>,
+  ) {}
+
+  public updateParticipant(
+    newParticipant: LocalParticipant | RemoteParticipant | undefined,
+  ): void {
+    if (this.participant$.value !== newParticipant) {
+      // Update the BehaviourSubject in the UserMedia.
+      this.participant$.next(newParticipant);
+    }
+  }
+
+  public destroy(): void {
+    this.scope.end();
+    this.vm.destroy();
+  }
+}
+
+export function sharingScreen$(p: Participant): Observable<boolean> {
+  return observeParticipantEvents(
+    p,
+    ParticipantEvent.TrackPublished,
+    ParticipantEvent.TrackUnpublished,
+    ParticipantEvent.LocalTrackPublished,
+    ParticipantEvent.LocalTrackUnpublished,
+  ).pipe(map((p) => p.isScreenShareEnabled));
+}
diff --git a/src/state/layout-types.ts b/src/state/layout-types.ts
new file mode 100644
index 00000000..3796715c
--- /dev/null
+++ b/src/state/layout-types.ts
@@ -0,0 +1,108 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import {
+  type GridTileViewModel,
+  type SpotlightTileViewModel,
+} from "./TileViewModel.ts";
+import {
+  type MediaViewModel,
+  type UserMediaViewModel,
+} from "./MediaViewModel.ts";
+
+export interface GridLayoutMedia {
+  type: "grid";
+  spotlight?: MediaViewModel[];
+  grid: UserMediaViewModel[];
+}
+
+export interface SpotlightLandscapeLayoutMedia {
+  type: "spotlight-landscape";
+  spotlight: MediaViewModel[];
+  grid: UserMediaViewModel[];
+}
+
+export interface SpotlightPortraitLayoutMedia {
+  type: "spotlight-portrait";
+  spotlight: MediaViewModel[];
+  grid: UserMediaViewModel[];
+}
+
+export interface SpotlightExpandedLayoutMedia {
+  type: "spotlight-expanded";
+  spotlight: MediaViewModel[];
+  pip?: UserMediaViewModel;
+}
+
+export interface OneOnOneLayoutMedia {
+  type: "one-on-one";
+  local: UserMediaViewModel;
+  remote: UserMediaViewModel;
+}
+
+export interface PipLayoutMedia {
+  type: "pip";
+  spotlight: MediaViewModel[];
+}
+
+export type LayoutMedia =
+  | GridLayoutMedia
+  | SpotlightLandscapeLayoutMedia
+  | SpotlightPortraitLayoutMedia
+  | SpotlightExpandedLayoutMedia
+  | OneOnOneLayoutMedia
+  | PipLayoutMedia;
+
+export interface GridLayout {
+  type: "grid";
+  spotlight?: SpotlightTileViewModel;
+  grid: GridTileViewModel[];
+  setVisibleTiles: (value: number) => void;
+}
+
+export interface SpotlightLandscapeLayout {
+  type: "spotlight-landscape";
+  spotlight: SpotlightTileViewModel;
+  grid: GridTileViewModel[];
+  setVisibleTiles: (value: number) => void;
+}
+
+export interface SpotlightPortraitLayout {
+  type: "spotlight-portrait";
+  spotlight: SpotlightTileViewModel;
+  grid: GridTileViewModel[];
+  setVisibleTiles: (value: number) => void;
+}
+
+export interface SpotlightExpandedLayout {
+  type: "spotlight-expanded";
+  spotlight: SpotlightTileViewModel;
+  pip?: GridTileViewModel;
+}
+
+export interface OneOnOneLayout {
+  type: "one-on-one";
+  local: GridTileViewModel;
+  remote: GridTileViewModel;
+}
+
+export interface PipLayout {
+  type: "pip";
+  spotlight: SpotlightTileViewModel;
+}
+
+/**
+ * A layout defining the media tiles present on screen and their visual
+ * arrangement.
+ */
+export type Layout =
+  | GridLayout
+  | SpotlightLandscapeLayout
+  | SpotlightPortraitLayout
+  | SpotlightExpandedLayout
+  | OneOnOneLayout
+  | PipLayout;
diff --git a/src/tile/GridTile.tsx b/src/tile/GridTile.tsx
index cbe7bf2e..421cefda 100644
--- a/src/tile/GridTile.tsx
+++ b/src/tile/GridTile.tsx
@@ -190,6 +190,7 @@ const UserMediaTile: FC<UserMediaTileProps> = ({
       currentReaction={reaction ?? undefined}
       raisedHandOnClick={raisedHandOnClick}
       localParticipant={vm.local}
+      focusUrl={vm.focusURL}
       audioStreamStats={audioStreamStats}
       videoStreamStats={videoStreamStats}
       {...props}
diff --git a/src/tile/MediaView.tsx b/src/tile/MediaView.tsx
index 8506a650..149b4177 100644
--- a/src/tile/MediaView.tsx
+++ b/src/tile/MediaView.tsx
@@ -46,6 +46,8 @@ interface Props extends ComponentProps<typeof animated.div> {
   localParticipant: boolean;
   audioStreamStats?: RTCInboundRtpStreamStats | RTCOutboundRtpStreamStats;
   videoStreamStats?: RTCInboundRtpStreamStats | RTCOutboundRtpStreamStats;
+  // The focus url, mainly for debugging purposes
+  focusUrl?: string;
 }
 
 export const MediaView: FC<Props> = ({
@@ -71,6 +73,7 @@ export const MediaView: FC<Props> = ({
   localParticipant,
   audioStreamStats,
   videoStreamStats,
+  focusUrl,
   ...props
 }) => {
   const { t } = useTranslation();
@@ -134,6 +137,7 @@ export const MediaView: FC<Props> = ({
           <RTCConnectionStats
             audio={audioStreamStats}
             video={videoStreamStats}
+            focusUrl={focusUrl}
           />
         )}
         {/* TODO: Bring this back once encryption status is less broken */}
diff --git a/src/tile/SpotlightTile.tsx b/src/tile/SpotlightTile.tsx
index b1a15332..6034c846 100644
--- a/src/tile/SpotlightTile.tsx
+++ b/src/tile/SpotlightTile.tsx
@@ -78,7 +78,7 @@ const SpotlightLocalUserMediaItem: FC<SpotlightLocalUserMediaItemProps> = ({
   ...props
 }) => {
   const mirror = useBehavior(vm.mirror$);
-  return <MediaView mirror={mirror} {...props} />;
+  return <MediaView mirror={mirror} focusUrl={vm.focusURL} {...props} />;
 };
 
 SpotlightLocalUserMediaItem.displayName = "SpotlightLocalUserMediaItem";
diff --git a/src/utils/displayname.ts b/src/utils/displayname.ts
index d2375897..8e989d3b 100644
--- a/src/utils/displayname.ts
+++ b/src/utils/displayname.ts
@@ -65,7 +65,7 @@ export function shouldDisambiguate(
   // displayname, after hidden character removal.
   return (
     memberships
-      .map((m) => m.sender && room.getMember(m.sender))
+      .map((m) => m.userId && room.getMember(m.userId))
       // NOTE: We *should* have a room member for everyone.
       .filter((m) => !!m)
       .filter((m) => m.userId !== userId)
diff --git a/src/utils/test-viewmodel.ts b/src/utils/test-viewmodel.ts
index 1b4d0cf0..d6a4bb10 100644
--- a/src/utils/test-viewmodel.ts
+++ b/src/utils/test-viewmodel.ts
@@ -49,7 +49,7 @@ export function getBasicRTCSession(
       getChildEventsForEvent: vitest.fn(),
     } as Partial<RelationsContainer> as RelationsContainer,
     client: {
-      getUserId: () => localRtcMember.sender,
+      getUserId: () => localRtcMember.userId,
       getDeviceId: () => localRtcMember.deviceId,
       getSyncState: () => SyncState.Syncing,
       sendEvent: vitest.fn().mockResolvedValue({ event_id: "$fake:event" }),
diff --git a/src/utils/test.ts b/src/utils/test.ts
index 2da8ed31..d50c1af4 100644
--- a/src/utils/test.ts
+++ b/src/utils/test.ts
@@ -196,7 +196,7 @@ export function mockRtcMembership(
     content: data,
   });
 
-  const cms = new CallMembership(event);
+  const cms = new CallMembership(event, data);
   vi.mocked(cms).getTransport = vi.fn().mockReturnValue(fociPreferred[0]);
   return cms;
 }
@@ -210,11 +210,11 @@ export function mockMatrixRoomMember(
 ): RoomMember {
   return {
     ...mockEmitter(),
-    userId: rtcMembership.sender,
+    userId: rtcMembership.userId,
     getMxcAvatarUrl(): string | undefined {
       return undefined;
     },
-    rawDisplayName: rtcMembership.sender,
+    rawDisplayName: rtcMembership.userId,
     ...member,
   } as RoomMember;
 }
@@ -274,6 +274,7 @@ export async function withLocalMedia(
       kind: E2eeType.PER_PARTICIPANT,
     },
     mockLivekitRoom({ localParticipant }),
+    "https://rtc-example.org",
     mediaDevices,
     constant(roomMember.rawDisplayName ?? "nodisplayname"),
     constant(null),
@@ -314,6 +315,7 @@ export async function withRemoteMedia(
       kind: E2eeType.PER_PARTICIPANT,
     },
     mockLivekitRoom({}, { remoteParticipants$: of([remoteParticipant]) }),
+    "https://rtc-example.org",
     constant(false),
     constant(roomMember.rawDisplayName ?? "nodisplayname"),
     constant(null),
diff --git a/vite.config.ts b/vite.config.ts
index cfc80279..a0bb9de5 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -97,6 +97,9 @@ export default ({
         cert: fs.readFileSync("./backend/dev_tls_m.localhost.crt"),
       },
     },
+    worker: {
+      format: "es",
+    },
     build: {
       minify: mode === "production" ? true : false,
       sourcemap: true,
diff --git a/yarn.lock b/yarn.lock
index ea44f40f..9d486c4f 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -10355,11 +10355,6 @@ __metadata:
     uuid: "npm:13"
   checksum: 10c0/6eedb93865419ca375f550c66801cd8f331833aed80ef16c49ad23b3eab648d3963571a2124d9737deb6ec909211d716949ad78d127268e16a8e2cc5b18d9fe1
   languageName: node
-  linkType: hard
-
-"matrix-widget-api@npm:^1.10.0, matrix-widget-api@npm:^1.13.0":
-  version: 1.13.1
-  resolution: "matrix-widget-api@npm:1.13.1"
   dependencies:
     "@types/events": "npm:^3.0.0"
     events: "npm:^3.2.0"