Logically separate the advertised transport from the active transport

To correctly implement the legacy "oldest membership" mode, we need the code to be more nuanced about the local transport. Specifically, it needs to allow for the transport we advertise in our membership to be different from the transport that we connect to and publish media on. Otherwise, if these two are yoked together, members will resend their memberships whenever an SFU hop occurs, which an attacker could use to cause an amplified wave of state changes.

src/state/CallViewModel/localMember/LocalMember.ts

@@ -62,7 +62,6 @@ import {
 } from "../remoteMembers/Connection.ts";
 import { type HomeserverConnected } from "./HomeserverConnected.ts";
 import { and$ } from "../../../utils/observable.ts";
-import { type LocalTransportWithSFUConfig } from "./LocalTransport.ts";
 
 export enum TransportState {
   /** Not even a transport is available to the LocalMembership */
@@ -128,7 +127,7 @@ interface Props {
   createPublisherFactory: (connection: Connection) => Publisher;
   joinMatrixRTC: (transport: LivekitTransportConfig) => void;
   homeserverConnected: HomeserverConnected;
-  localTransport$: Behavior<LocalTransportWithSFUConfig | null>;
+  localTransport$: Behavior<LivekitTransportConfig | null>;
   matrixRTCSession: Pick<
     MatrixRTCSession,
     "updateCallIntent" | "leaveRoomSession"
@@ -147,7 +146,7 @@ interface Props {
  * @param props.createPublisherFactory Factory to create a publisher once we have a connection.
  * @param props.joinMatrixRTC Callback to join the matrix RTC session once we have a transport.
  * @param props.homeserverConnected The homeserver connected state.
- * @param props.localTransport$ The local transport to use for publishing.
+ * @param props.localTransport$ The transport to advertise in our membership.
  * @param props.logger The logger to use.
  * @param props.muteStates The mute states for video and audio.
  * @param props.matrixRTCSession The matrix RTC session to join.
@@ -237,9 +236,7 @@ export const createLocalMembership$ = ({
           return null;
         }
 
-        return connectionData.getConnectionForTransport(
-          localTransport.transport,
-        );
+        return connectionData.getConnectionForTransport(localTransport);
       }),
       tap((connection) => {
         logger.info(
@@ -549,7 +546,7 @@ export const createLocalMembership$ = ({
       if (!shouldConnect) return;
 
       try {
-        joinMatrixRTC(transport.transport);
+        joinMatrixRTC(transport);
       } catch (error) {
         logger.error("Error entering RTC session", error);
         if (error instanceof Error)