feat(gateway): detect pre-existing streamers on bot voice join

If someone is ALREADY sharing screen / camera on when the bot joins the
channel, no voiceStateUpdate with streaming:true fires for them, so the
bot never sent STREAM_WATCH and missed their video entirely. trackChannel
now scans channel.members and starts a watch for anyone already streaming
(ignoring the bot itself and non-streamers). Idempotent: startStreamWatch
no-ops if a watch already exists. +2 tests (9/9 in videoRecorder).

services/discord-gateway/src/modules/voice-recording/streamWatchReceiver.ts

@@ -271,7 +271,7 @@ function connectWatch(
     handleUdpMessage(watchKey, netAny, uidProps, msg);
   };
 
-  net.on("stateChange", (newState, oldState) => {
+  net.on("stateChange", (oldState, newState) => {
     const s = newState as { code?: number };
     const code = s?.code;
     const oldCode = (oldState as { code?: number })?.code;

services/discord-gateway/src/modules/voice-recording/videoRecorder.ts

@@ -78,6 +78,36 @@ export function setVideoRecorderClient(client: Client | undefined) {
 /** Register a channel whose audio recording is active (video should follow). */
 export function trackChannel(guildId: string, channel: VoiceChannel) {
   watchedChannels.set(guildId, channel);
+  // When the bot joins a channel that ALREADY has people streaming (screen
+  // share / camera on BEFORE the bot joined), no voiceStateUpdate with
+  // streaming:true fires for them. Scan every member now and start watching
+  // anyone already streaming, so we don't miss a live stream in progress.
+  scanExistingStreamers(channel);
+}
+
+/**
+ * Scan all members currently in `channel` and start watching anyone whose
+ * voice state has `streaming` set (screen share / camera already on when the
+ * bot joined). Fire-and-forget per member — idempotent (startStreamWatch is
+ * a no-op if a watch already exists for that user).
+ */
+export function scanExistingStreamers(channel: VoiceChannel): void {
+  const members = channel.members;
+  if (!members || members.size === 0) return;
+  let watched = 0;
+  for (const [, member] of members) {
+    const vs = member.voice?.streaming;
+    if (vs && member.id !== _client?.user?.id) {
+      startVideoRecording(channel, member.id);
+      watched++;
+    }
+  }
+  if (watched > 0) {
+    logger.info(
+      { guildId: channel.guild.id, watched },
+      "Scanned pre-existing streamers on join",
+    );
+  }
 }
 
 /** Unregister a channel (voice stopped). Tear down any video watches. */

services/discord-gateway/tests/videoRecorder.test.ts

@@ -101,4 +101,29 @@ describe("videoRecorder (stream-watch orchestration)", () => {
     listener(null, { id: "u1", guild: { id: "g1" }, channelId: "c1", streaming: false });
     expect(stopSpy).toHaveBeenCalledWith("g1", "u1");
   });
+
+  it("trackChannel scans pre-existing streamers already in the channel (bot join case)", () => {
+    const client = makeClient() as any;
+    setVideoRecorderClient(client);
+    const spy = vi.spyOn(streamWatch, "startStreamWatch").mockImplementation(() => {});
+    const ch = {
+      id: "c1",
+      guild: { id: "g1" },
+      members: new Map([
+        ["u1", { id: "u1", voice: { streaming: true } }], // already streaming
+        ["u2", { id: "u2", voice: { streaming: false } }], // not streaming
+        ["bot1", { id: "bot1", voice: { streaming: true } }], // bot itself
+      ]),
+    };
+    trackChannel("g1", ch as any);
+    // only the already-streaming non-bot member gets watched
+    expect(spy).toHaveBeenCalledTimes(1);
+    expect(spy).toHaveBeenCalledWith(ch, "u1");
+  });
+
+  it("trackChannel is a no-op when the channel has no members (or none streaming)", () => {
+    const spy = vi.spyOn(streamWatch, "startStreamWatch").mockImplementation(() => {});
+    trackChannel("g1", makeChannel()); // no members
+    expect(spy).not.toHaveBeenCalled();
+  });
 });