feat(lotus-denoise): AGC off for ML tier + init/build leak hardening

AEC/AGC audit fix + two hardening items from the engine review.

- Add an `autoGainControl` capture param (UrlParams -> CallViewModel ->
  ConnectionFactory audioCaptureDefaults), mirroring echoCancellation/
  noiseSuppression. Defaults true (unchanged); the host sets it false only for
  the ML tier so the browser's auto gain control doesn't fight the in-source ML
  denoiser (pumping). Echo cancellation stays on. Tests cover the URL parse and
  the audioCaptureDefaults wiring.
- L1: init() now closes the owned AudioContext on a build failure (was orphaned;
  browsers cap live contexts, so repeated failures could exhaust them).
- L2: buildGraph() disposes its partially-built nodes on failure (disposeGraph
  previously only cleaned the prior graph).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/state/CallViewModel/CallViewModel.ts

@@ -504,6 +504,7 @@ export function createCallViewModel$(
       options.livekitRoomFactory,
       getUrlParams().echoCancellation,
       getUrlParams().noiseSuppression,
+      getUrlParams().autoGainControl,
     );
 
   const connectionManager = createConnectionManager$({

src/state/CallViewModel/remoteMembers/ConnectionFactory.ts

@@ -55,6 +55,7 @@ export class ECConnectionFactory implements ConnectionFactory {
    * @param livekitRoomFactory - Optional factory function (for testing) to create LivekitRoom instances. If not provided, a default factory is used.
    * @param echoCancellation - Whether to enable echo cancellation for audio capture.
    * @param noiseSuppression - Whether to enable noise suppression for audio capture.
+   * @param autoGainControl - Whether to enable auto gain control for audio capture.
    */
   public constructor(
     private client: OpenIDClientParts,
@@ -66,6 +67,7 @@ export class ECConnectionFactory implements ConnectionFactory {
     livekitRoomFactory?: () => LivekitRoom,
     echoCancellation: boolean = true,
     noiseSuppression: boolean = true,
+    autoGainControl: boolean = true,
   ) {
     const defaultFactory = (): LivekitRoom =>
       new LivekitRoom(
@@ -81,6 +83,7 @@ export class ECConnectionFactory implements ConnectionFactory {
           controlledAudioDevices: this.controlledAudioDevices,
           echoCancellation,
           noiseSuppression,
+          autoGainControl,
         }),
       );
     this.livekitRoomFactory = livekitRoomFactory ?? defaultFactory;
@@ -127,6 +130,7 @@ function generateRoomOption({
   controlledAudioDevices,
   echoCancellation,
   noiseSuppression,
+  autoGainControl,
 }: {
   devices: MediaDevices;
   processorState: ProcessorState;
@@ -137,6 +141,7 @@ function generateRoomOption({
   controlledAudioDevices: boolean;
   echoCancellation: boolean;
   noiseSuppression: boolean;
+  autoGainControl: boolean;
 }): RoomOptions {
   return {
     ...defaultLiveKitOptions,
@@ -150,6 +155,7 @@ function generateRoomOption({
       deviceId: devices.audioInput.selected$.value?.id,
       echoCancellation,
       noiseSuppression,
+      autoGainControl,
     },
     audioOutput: {
       // When using controlled audio devices, we don't want to set the

src/state/CallViewModel/remoteMembers/ECConnectionFactory.test.ts

@@ -53,14 +53,13 @@ beforeEach(() => {
 
 describe("ECConnectionFactory - Audio inputs options", () => {
   test.each([
-    { echo: true, noise: true },
-    { echo: true, noise: false },
-    { echo: false, noise: true },
-    { echo: false, noise: false },
+    { echo: true, noise: true, agc: true },
+    { echo: true, noise: false, agc: false },
+    { echo: false, noise: true, agc: false },
+    { echo: false, noise: false, agc: true },
   ])(
-    "it sets echoCancellation=$echo and noiseSuppression=$noise based on constructor parameters",
-    ({ echo, noise }) => {
-      // test("it sets echoCancellation and noiseSuppression based on constructor parameters", () => {
+    "it sets echoCancellation=$echo, noiseSuppression=$noise, autoGainControl=$agc based on constructor parameters",
+    ({ echo, noise, agc }) => {
       const RoomConstructor = vi.mocked(LivekitRoom);
 
       const ecConnectionFactory = new ECConnectionFactory(
@@ -76,6 +75,7 @@ describe("ECConnectionFactory - Audio inputs options", () => {
         undefined,
         echo,
         noise,
+        agc,
       );
       ecConnectionFactory.createConnection(
         testScope,
@@ -90,6 +90,7 @@ describe("ECConnectionFactory - Audio inputs options", () => {
           audioCaptureDefaults: expect.objectContaining({
             echoCancellation: echo,
             noiseSuppression: noise,
+            autoGainControl: agc,
           }),
         }),
       );