fix: auto-disable AEC during screen share to prevent Chrome voice ducking

Chrome's AEC uses getDisplayMedia audio as a reference signal and
aggressively ducks the microphone even when headphones are used.
This adds a screenShareActive flag to AudioManager that forces
echoCancellation off during screen share, plus Chromium-specific
goog* constraints as belt-and-suspenders.

packages/web/src/audio/AudioManager.ts

@@ -17,6 +17,7 @@ export class AudioManager {
   private voiceEchoCancellation = true;
   private voiceNoiseSuppression = true;
   private voiceAutoGainControl = false;
+  private screenShareActive = false;
   private streamGeneration = 0;
 
   private constructor() {}
@@ -141,13 +142,25 @@ export class AudioManager {
         this.currentStream.getTracks().forEach(t => t.stop());
       }
 
+      // When screen sharing with audio, Chrome's AEC uses the getDisplayMedia
+      // audio as a reference signal and ducks the mic — even with headphones.
+      // Force AEC off during screen share to prevent this.
+      const effectiveEchoCancellation = this.screenShareActive ? false : this.voiceEchoCancellation;
+
       const constraints = {
         audio: {
           deviceId: deviceId === 'default' ? undefined : { exact: deviceId },
-          echoCancellation: this.voiceEchoCancellation,
+          echoCancellation: effectiveEchoCancellation,
           noiseSuppression: this.voiceNoiseSuppression,
           autoGainControl: this.voiceAutoGainControl,
-        }
+          // Chromium-specific constraints — belt-and-suspenders to ensure
+          // Chrome's internal audio engine respects the standard constraints.
+          googEchoCancellation: effectiveEchoCancellation,
+          googAutoGainControl: this.voiceAutoGainControl,
+          googNoiseSuppression: this.voiceNoiseSuppression,
+          googHighpassFilter: false,
+          googTypingNoiseDetection: false,
+        } as any
       };
 
       this.currentStream = await navigator.mediaDevices.getUserMedia(constraints);
@@ -197,6 +210,22 @@ export class AudioManager {
     }
   }
 
+  /**
+   * When screen sharing with audio is active, Chrome's AEC uses the screen
+   * share audio as a reference signal and aggressively ducks the microphone.
+   * Setting this flag forces echoCancellation OFF regardless of user preference,
+   * severing the software link that causes the ducking.
+   */
+  setScreenShareActive(active: boolean) {
+    if (this.screenShareActive === active) return;
+    this.screenShareActive = active;
+    console.log(`[AudioManager] Screen share active: ${active} — ${active ? 'forcing AEC off' : 'restoring user AEC preference'}`);
+    if (this.currentStream) {
+      this.currentStream.getTracks().forEach(t => t.stop());
+      this.currentStream = null;
+    }
+  }
+
   getStreamGeneration(): number {
     return this.streamGeneration;
   }

packages/web/src/components/modals/UserSettings.tsx

@@ -127,13 +127,13 @@ export function UserSettingsModal() {
             Voice Processing
           </h3>
           <p className="text-xs text-discord-text-muted mb-3">
-            Disable Auto Gain Control when streaming to prevent your browser from ducking your microphone.
+            Echo Cancellation is automatically disabled while you screen share to prevent Chrome from ducking your mic volume.
           </p>
 
           <div className="flex items-center justify-between py-2">
             <div>
               <div className="text-sm text-discord-text-primary">Echo Cancellation</div>
-              <div className="text-xs text-discord-text-muted">Removes echo when using speakers</div>
+              <div className="text-xs text-discord-text-muted">Removes echo when using speakers (auto-disabled during screen share)</div>
             </div>
             <button
               onClick={() => setEchoCancellation(!echoCancellation)}

packages/web/src/components/voice/DmCallView.tsx

@@ -4,6 +4,7 @@ import { useServerStore } from '../../stores/serverStore';
 import { useAuthStore } from '../../stores/authStore';
 import { getActiveRoom } from '../../hooks/useLiveKit';
 import { wsSend } from '../../hooks/useWebSocket';
+import { AudioManager } from '../../audio/AudioManager';
 import { VideoPresets, VideoPreset } from 'livekit-client';
 
 const QUALITY_MAP: Record<string, any> = {
@@ -94,9 +95,11 @@ export function DmCallView() {
     if (!room) return;
     try {
       if (!isScreenSharing) {
+        AudioManager.getInstance().setScreenShareActive(true);
         await room.localParticipant.setScreenShareEnabled(true, { audio: true });
       } else {
         await room.localParticipant.setScreenShareEnabled(false);
+        AudioManager.getInstance().setScreenShareActive(false);
       }
       toggleScreenShare();
     } catch (err) {

packages/web/src/components/voice/StreamTile.tsx

@@ -2,6 +2,7 @@ import React, { useRef, useEffect, useState, useCallback } from 'react';
 import { Avatar } from '../ui/Avatar';
 import { useVoiceStore } from '../../stores/voiceStore';
 import { getActiveRoom, setStreamSubscription } from '../../hooks/useLiveKit';
+import { AudioManager } from '../../audio/AudioManager';
 import { VideoQualityPopover } from './VideoQualityPopover';
 import type { StreamTile as StreamTileType } from '../../hooks/useLiveKit';
 
@@ -107,6 +108,7 @@ export function StreamTile({ tile, large }: StreamTileProps) {
     const room = getActiveRoom();
     if (room) {
       await room.localParticipant.setScreenShareEnabled(false);
+      AudioManager.getInstance().setScreenShareActive(false);
       useVoiceStore.getState().toggleScreenShare();
     }
   }, []);

packages/web/src/components/voice/VoiceControlBar.tsx

@@ -3,6 +3,7 @@ import { useVoiceStore } from '../../stores/voiceStore';
 import { useUIStore } from '../../stores/uiStore';
 import { getActiveRoom } from '../../hooks/useLiveKit';
 import { wsSend } from '../../hooks/useWebSocket';
+import { AudioManager } from '../../audio/AudioManager';
 import { VideoQualityPopover } from './VideoQualityPopover';
 import { VideoPresets, VideoPreset } from 'livekit-client';
 
@@ -97,9 +98,11 @@ export function VoiceControlBar() {
     if (!room) return;
     try {
       if (!isScreenSharing) {
+        AudioManager.getInstance().setScreenShareActive(true);
         await room.localParticipant.setScreenShareEnabled(true, { audio: true });
       } else {
         await room.localParticipant.setScreenShareEnabled(false);
+        AudioManager.getInstance().setScreenShareActive(false);
       }
       toggleScreenShare();
     } catch (err) {

packages/web/src/components/voice/VoiceControls.tsx

@@ -3,6 +3,7 @@ import { useVoiceStore } from '../../stores/voiceStore';
 import { useServerStore } from '../../stores/serverStore';
 import { getActiveRoom } from '../../hooks/useLiveKit';
 import { wsSend } from '../../hooks/useWebSocket';
+import { AudioManager } from '../../audio/AudioManager';
 import { VideoQualityPopover } from './VideoQualityPopover';
 
 /**
@@ -43,9 +44,11 @@ export function VoiceControls() {
     if (!room) return;
     try {
       if (!isScreenSharing) {
+        AudioManager.getInstance().setScreenShareActive(true);
         await room.localParticipant.setScreenShareEnabled(true, { audio: true });
       } else {
         await room.localParticipant.setScreenShareEnabled(false);
+        AudioManager.getInstance().setScreenShareActive(false);
       }
       toggleScreenShare();
     } catch (err) {

packages/web/src/hooks/useLiveKit.ts

@@ -251,6 +251,8 @@ export function useLiveKit() {
 
         // Sync voice processing settings to AudioManager
         audioManager.setVoiceProcessing({ echoCancellation, noiseSuppression, autoGainControl });
+        // Keep screen share state in sync (handles edge cases like remounts)
+        audioManager.setScreenShareActive(isScreenSharing);
 
         // If muted or deafened, unpublish mic
         if (isMuted || isDeafened) {
@@ -305,7 +307,7 @@ export function useLiveKit() {
     return () => {
       unsubscribe();
     };
-  }, [isMuted, isDeafened, inputDeviceId, inputVolume, isConnected, echoCancellation, noiseSuppression, autoGainControl]);
+  }, [isMuted, isDeafened, inputDeviceId, inputVolume, isConnected, echoCancellation, noiseSuppression, autoGainControl, isScreenSharing]);
 
   const connect = useCallback(async (channelId: string) => {
     if (connectedChannelRef.current === channelId && roomRef.current?.state === ConnectionState.Connected) return;
@@ -643,6 +645,10 @@ export function useLiveKit() {
   const toggleScreenShare = useCallback(async () => {
     if (roomRef.current) {
       if (!isScreenSharing) {
+        // Notify AudioManager BEFORE enabling screen share so the mic track
+        // gets republished with AEC off, preventing Chrome's ducking.
+        AudioManager.getInstance().setScreenShareActive(true);
+
         const preset = QUALITY_MAP[videoQuality] || AUTO_PRESET;
         const track = await roomRef.current.localParticipant.setScreenShareEnabled(true, {
           audio: true,
@@ -669,7 +675,11 @@ export function useLiveKit() {
           }, 2000);
           setTimeout(() => applyOverdriveHammer(roomRef.current!, Track.Source.ScreenShare, preset), 5000);
         }
-      } else { await roomRef.current.localParticipant.setScreenShareEnabled(false); }
+      } else {
+        await roomRef.current.localParticipant.setScreenShareEnabled(false);
+        // Restore user's AEC preference after screen share ends
+        AudioManager.getInstance().setScreenShareActive(false);
+      }
       updateParticipants();
     }
   }, [isScreenSharing, videoQuality, updateParticipants]);