add support for sending data to the rtcSdk

playwright/sdk/data.spec.ts

@@ -0,0 +1,41 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { expect, test } from "@playwright/test";
+
+import { startPair, tileOf } from "./harness";
+
+test.describe.configure({ timeout: 300_000 });
+
+test("a message sent beside the media reaches the peer, and only the peer", async ({
+  browser,
+}) => {
+  const { pages, users } = await startPair(browser, "sdkdata");
+  const [sender, receiver] = pages;
+  // Both are in the call before anything is sent, so the receiver knows the
+  // sender as a member and does not drop the message
+  for (const page of pages)
+    await expect(page.getByTestId("member")).toHaveCount(2, {
+      timeout: 60_000,
+    });
+  await expect(tileOf(receiver, users[0])).toBeVisible();
+
+  await sender.getByPlaceholder("message").fill("hello from the SDK");
+  await sender.getByRole("button", { name: "Send" }).click();
+
+  const message = receiver.getByTestId("message");
+  await expect(message).toHaveText(
+    `${users[0].displayName}: hello from the SDK`,
+    {
+      timeout: 30_000,
+    },
+  );
+  await expect(message).toHaveAttribute("data-topic", "chat");
+  await expect(message).toHaveAttribute("data-user-id", users[0].userId);
+  // Our own messages are not echoed back
+  await expect(sender.getByTestId("message")).toHaveCount(0);
+});