fix(backend): handle voice PCM as JSON instead of binary

- Add discord:voice:pcm to SUBSCRIPTIONS as regular JSON channel
- Remove BINARY_CHANNELS and handleBinaryMessage function
- Discord-gateway sends PCM as JSON with base64, not raw binary
- This fixes PCM data not reaching browser via WebSocket

The issue was backend expected binary format but gateway sends:
{"type":"voice_pcm_data","data":{"userId":"...","pcm":"base64..."}}

Now backend correctly subscribes and broadcasts this to WebSocket clients.

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

services/backend/src/ws/redis-bridge.ts

@@ -26,11 +26,9 @@ const SUBSCRIPTIONS: ChannelMapping[] = [
     eventType: "analysis_queue_status",
   },
   { channel: "discord:voice:active_user", eventType: "voice_active_user" },
+  { channel: "discord:voice:pcm", eventType: "voice_pcm_data" },
 ];
 
-// Binary channels that need special handling (messageBuffer event)
-const BINARY_CHANNELS = ["discord:voice:pcm"];
-
 let subscriber: Redis | null = null;
 
 function createSubscriber(): Redis {
@@ -94,41 +92,6 @@ function handleSubscriptionMessage(channel: string, message: string): void {
   broadcastRaw(mapping.eventType, data);
 }
 
-/**
- * Handle binary messages from Redis (e.g. voice PCM data).
- * Expected format: 4-byte userId hash + PCM buffer
- */
-function handleBinaryMessage(channel: Buffer, message: Buffer): void {
-  const channelStr = channel.toString();
-
-  if (channelStr === "discord:voice:pcm") {
-    if (message.length < 4) {
-      logger.warn(
-        { channel: channelStr, size: message.length },
-        "Received PCM message too short to contain userId",
-      );
-      return;
-    }
-
-    // First 4 bytes = userId hash, rest = PCM data
-    const userIdHash = message.readUInt32LE(0);
-    const pcmData = message.subarray(4);
-
-    logger.debug(
-      { channel: channelStr, userIdHash, pcmSize: pcmData.length },
-      "Broadcasting voice PCM data",
-    );
-
-    // Broadcast as binary: userId (4 bytes) + PCM data
-    broadcastRaw("voice_pcm", message);
-  } else {
-    logger.warn(
-      { channel: channelStr },
-      "Received binary message for unmapped channel",
-    );
-  }
-}
-
 export async function startRedisBridge(): Promise<void> {
   if (!config.REDIS_URL && !config.REDIS_HOST) {
     logger.info("Redis not configured, skipping Redis bridge");
@@ -155,7 +118,6 @@ export async function startRedisBridge(): Promise<void> {
     });
 
     subscriber.on("message", handleSubscriptionMessage);
-    subscriber.on("messageBuffer", handleBinaryMessage);
 
     await subscriber.ping();
     logger.info("Redis ping OK");
@@ -164,11 +126,6 @@ export async function startRedisBridge(): Promise<void> {
     await subscriber.subscribe(...channels);
     logger.info({ channels }, "Subscribed to Redis channels");
 
-    if (BINARY_CHANNELS.length > 0) {
-      await subscriber.subscribe(...BINARY_CHANNELS);
-      logger.info({ channels: BINARY_CHANNELS }, "Subscribed to binary Redis channels");
-    }
-
     logger.info("Redis bridge started");
   } catch (err) {
     logger.error({ err }, "Failed to start Redis bridge");