fix(media): guard SynchronizedMedia.frameDomain before reading frameRate

packages/media/src/identity.ts

@@ -169,6 +169,7 @@ export function synchronizedMediaSampleFrames(value: SynchronizedMedia): number
 
 export function verifySynchronizedMedia(value: unknown): asserts value is SynchronizedMedia {
   const item = object(value, "SynchronizedMedia") as unknown as SynchronizedMedia;
+  object(item.frameDomain, "SynchronizedMedia.frameDomain");
   verifyRational(item.frameDomain.frameRate, "SynchronizedMedia.frameDomain.frameRate");
   positiveInteger(item.frameDomain.frameCount, "SynchronizedMedia.frameDomain.frameCount");
   synchronizedMediaSampleFrames(item);

packages/media/test/identity.test.ts

@@ -0,0 +1,36 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import { verifySynchronizedMedia } from "../src/index.js";
+import type { SynchronizedMedia } from "../src/index.js";
+import { fixtureResource } from "../../../test/fixture-resource.js";
+
+const media: SynchronizedMedia = {
+  frameDomain: { frameRate: { numerator: 30, denominator: 1 }, frameCount: 60 },
+  visual: {
+    artifact: { kind: "blob", resource: fixtureResource("identity:visual"), size: 1, mediaType: "video/mp4" },
+    width: 1920, height: 1080,
+  },
+  audio: { artifact: { kind: "blob", resource: fixtureResource("identity:audio"), size: 1, mediaType: "audio/wav" } },
+};
+
+test("verifySynchronizedMedia accepts a well-formed value", () => {
+  assert.doesNotThrow(() => verifySynchronizedMedia(media));
+});
+
+test("verifySynchronizedMedia rejects a missing frame domain with a stated error", () => {
+  const { frameDomain: _omitted, ...withoutFrameDomain } = media;
+  assert.throws(
+    () => verifySynchronizedMedia(withoutFrameDomain),
+    /SynchronizedMedia\.frameDomain must be an object/,
+  );
+});
+
+test("verifySynchronizedMedia rejects a non-object frame domain with a stated error", () => {
+  for (const frameDomain of [null, "30/1", 30] as const) {
+    assert.throws(
+      () => verifySynchronizedMedia({ ...media, frameDomain }),
+      /SynchronizedMedia\.frameDomain must be an object/,
+    );
+  }
+});