diff --git a/src/lotus/lotusAudioInject.test.ts b/src/lotus/lotusAudioInject.test.ts
index f919661f..9570df11 100644
--- a/src/lotus/lotusAudioInject.test.ts
+++ b/src/lotus/lotusAudioInject.test.ts
@@ -11,6 +11,7 @@ import { of } from "rxjs";
 
 import { type CallViewModel } from "../state/CallViewModel/CallViewModel";
 import {
+  canPublishSoundboard,
   MAX_INJECT_BYTES,
   parseInjectSource,
   startLotusAudioInject,
@@ -258,3 +259,17 @@ test("parseInjectSource rejects oversized or non-buffer audio", () => {
   expect(parseInjectSource({ audio: "not bytes" })).toBeNull();
   expect(parseInjectSource({ audio: new Uint8Array(4) })).toBeNull();
 });
+
+test("canPublishSoundboard: refused by a microphone-only grant (EC #47)", () => {
+  expect(canPublishSoundboard(undefined)).toBe(true);
+  expect(
+    canPublishSoundboard({ canPublish: true, canPublishSources: [] }),
+  ).toBe(true);
+  expect(
+    canPublishSoundboard({ canPublish: true, canPublishSources: [2] }),
+  ).toBe(false);
+  expect(
+    canPublishSoundboard({ canPublish: true, canPublishSources: [2, 0] }),
+  ).toBe(true);
+  expect(canPublishSoundboard({ canPublish: false })).toBe(false);
+});
diff --git a/src/lotus/lotusAudioInject.ts b/src/lotus/lotusAudioInject.ts
index 59b2fb3a..19a16485 100644
--- a/src/lotus/lotusAudioInject.ts
+++ b/src/lotus/lotusAudioInject.ts
@@ -60,6 +60,22 @@ function acquireSharedAudio(): {
  * No effect unless the host sends the action. Returns a teardown function that
  * also aborts any clip still playing.
  */
+/**
+ * Pure: whether these LiveKit permissions allow publishing the soundboard's
+ * Unknown-source track (EC #47). No permissions or an empty source list
+ * means unrestricted; otherwise UNKNOWN (TrackSource 0) must be allowed.
+ */
+export function canPublishSoundboard(
+  perm:
+    | { canPublish?: boolean; canPublishSources?: readonly number[] }
+    | undefined,
+): boolean {
+  if (!perm) return true;
+  if (perm.canPublish === false) return false;
+  const sources = perm.canPublishSources ?? [];
+  return sources.length === 0 || sources.includes(0);
+}
+
 export function startLotusAudioInject(vm: CallViewModel): () => void {
   const w = widget;
   if (!w) return () => undefined;
@@ -116,6 +132,19 @@ export function startLotusAudioInject(vm: CallViewModel): () => void {
       return;
     }
 
+    // [EC #47] Clips publish as an Unknown-source track. Audio-only rooms get
+    // a token limited to the microphone source, where LiveKit refuses that
+    // publish *after* we replied; say so up front instead of failing silently.
+    if (
+      rooms.some((r) => !canPublishSoundboard(r.localParticipant.permissions))
+    ) {
+      w.api.transport.reply(ev.detail, {
+        played: false,
+        reason: "not_permitted",
+      });
+      return;
+    }
+
     w.api.transport.reply(ev.detail, {});
     void playInjectedClip(clip, volume, rooms, activeClips).catch((e) =>
       logger.warn("[lotus] inject_audio failed", e),