feat(lotus): work when served from its own origin (cinny #43)

Two things tied EC to the host's origin:

- Widget message check: matrix-widget-api's strictOriginCheck compares
  ev.origin with THIS frame's origin, so on call.chat.lotusguild.org every
  message from chat.lotusguild.org would be dropped and calls would not
  start. restrictToHost() instead requires ev.source === window.parent and
  ev.origin === parentUrl's origin. Same-origin deployments keep working
  (the host origin is our own origin there), and it is stricter than
  before: the sender must also be our parent window.
- Soundboard: the host's blob: clip URL is origin-bound. io.lotus.inject_audio
  now accepts the clip's bytes (`audio`, ArrayBuffer, <= 8 MiB) and prefers
  them over `url`; hosts that only send `url` are unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/lotus/lotusAudioInject.ts

@@ -52,8 +52,10 @@ function acquireSharedAudio(): {
  * that was impossible against the prebuilt EC bundle (LiveKit's
  * LocalParticipant lived in EC's module scope).
  *
- * Action data: `{ url: string, volume?: number }`. `url` must be an https/blob
- * URL (the host resolves mxc → media URL).
+ * Action data: `{ url?: string, audio?: ArrayBuffer, volume?: number }`.
+ * `audio` is the clip's bytes (cinny #43: a host `blob:` URL can't be fetched
+ * once EC is served from its own origin, so the host sends the bytes and they
+ * win); otherwise `url` must be an https/blob URL (older hosts).
  *
  * No effect unless the host sends the action. Returns a teardown function that
  * also aborts any clip still playing.
@@ -88,12 +90,12 @@ export function startLotusAudioInject(vm: CallViewModel): () => void {
       return;
     }
     const data = ev.detail.data as
-      | { url?: unknown; volume?: unknown }
+      | { url?: unknown; audio?: unknown; volume?: unknown }
       | undefined;
-    const url = typeof data?.url === "string" ? safeMediaUrl(data.url) : null;
-    if (!url) {
+    const clip = parseInjectSource(data);
+    if (!clip) {
       w.api.transport.reply(ev.detail, {});
-      logger.warn("[lotus] inject_audio: missing/invalid url");
+      logger.warn("[lotus] inject_audio: missing/invalid url or audio");
       return;
     }
     const volume =
@@ -115,7 +117,7 @@ export function startLotusAudioInject(vm: CallViewModel): () => void {
     }
 
     w.api.transport.reply(ev.detail, {});
-    void playInjectedClip(url, volume, rooms, activeClips).catch((e) =>
+    void playInjectedClip(clip, volume, rooms, activeClips).catch((e) =>
       logger.warn("[lotus] inject_audio failed", e),
     );
   };
@@ -144,6 +146,27 @@ export function startLotusAudioInject(vm: CallViewModel): () => void {
   };
 }
 
+/** Largest clip accepted as bytes (the host's soundboard clips are small). */
+export const MAX_INJECT_BYTES = 8 * 1024 * 1024;
+
+/**
+ * The clip to play: the bytes the host sent (`audio`), or else a fetchable
+ * `url`. Exported for tests.
+ */
+export function parseInjectSource(
+  data: { url?: unknown; audio?: unknown } | undefined,
+): string | ArrayBuffer | null {
+  const audio = data?.audio;
+  if (
+    audio instanceof ArrayBuffer &&
+    audio.byteLength > 0 &&
+    audio.byteLength <= MAX_INJECT_BYTES
+  ) {
+    return audio;
+  }
+  return typeof data?.url === "string" ? safeMediaUrl(data.url) : null;
+}
+
 /** Only allow fetchable media URLs; never same-origin credentialed GETs etc. */
 function safeMediaUrl(raw: string): string | null {
   try {
@@ -155,7 +178,7 @@ function safeMediaUrl(raw: string): string | null {
 }
 
 async function playInjectedClip(
-  url: string,
+  clip: string | ArrayBuffer,
   volume: number,
   rooms: LivekitRoom[],
   activeClips: Set<() => void>,
@@ -188,25 +211,30 @@ async function playInjectedClip(
   };
   activeClips.add(placeholder);
 
-  let resp: Response;
-  try {
-    resp = await fetch(url, {
-      credentials: "omit",
-      mode: "cors",
-      signal: controller.signal,
-    });
-  } catch (e) {
-    // Superseded by a newer clip mid-fetch — expected, not a failure.
+  let arrayBuffer: ArrayBuffer;
+  if (typeof clip !== "string") {
+    arrayBuffer = clip;
+  } else {
+    let resp: Response;
+    try {
+      resp = await fetch(clip, {
+        credentials: "omit",
+        mode: "cors",
+        signal: controller.signal,
+      });
+    } catch (e) {
+      // Superseded by a newer clip mid-fetch — expected, not a failure.
+      if (aborted) return;
+      throw e;
+    }
+    if (aborted) return;
+    if (!resp.ok) {
+      activeClips.delete(placeholder);
+      throw new Error(`fetch ${clip} -> ${resp.status}`);
+    }
+    arrayBuffer = await resp.arrayBuffer();
     if (aborted) return;
-    throw e;
   }
-  if (aborted) return;
-  if (!resp.ok) {
-    activeClips.delete(placeholder);
-    throw new Error(`fetch ${url} -> ${resp.status}`);
-  }
-  const arrayBuffer = await resp.arrayBuffer();
-  if (aborted) return;
 
   // [lotus] Reuse the shared module-level context/destination (#14) rather
   // than `new AudioContext()` per clip — see the declaration above.