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

embedded/web/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@lotusguild/element-call-embedded",
-  "version": "0.25.0-lotus.16",
+  "version": "0.25.0-lotus.20",
   "files": [
     "README.md",
     "LICENSE-AGPL-3.0",

src/index.css

@@ -90,16 +90,29 @@ body.lotus-transparent[data-background="gradient"]::before {
   display: none !important;
 }
 
+/* [cinny #43] lotusHostControls=1: the host renders its own call bar, so EC's
+footer is hidden (kept in the DOM but out of the layout flow). */
+body.lotus-host-controls [data-testid="footer-container"] {
+  position: absolute !important;
+  visibility: hidden !important;
+}
+
 /* [lotus] Native Lotus/TDS theme, applied when lotusTheme=1, instead of the
 host injecting CSS into the iframe after load. Overrides Compound design tokens
 with Lotus values at the source so theming is complete and flash-free. Extend
 this block with the full Lotus token map from the design system; the canvas
 override below is a safe starting point that matches the Lotus dark surface. */
 body.lotus-theme {
-  --cpd-color-bg-canvas-default: #0c0d10;
   --video-tile-background: var(--cpd-color-bg-subtle-secondary);
 }
 
+/* Dark themes only: in the light theme this near-black canvas sat behind
+light-theme (dark) text, e.g. the tile name tags were unreadable. */
+body.lotus-theme.cpd-theme-dark,
+body.lotus-theme.cpd-theme-dark-hc {
+  --cpd-color-bg-canvas-default: #0c0d10;
+}
+
 /* [lotus #21] Subtle contrast guard for elements that sit directly on the
 transparent canvas (no opaque tile background behind them) when
 lotusTransparent is set: the host's real wallpaper is unknown to us, so a

src/lotus/LotusFrameScreenshare.module.css

@@ -0,0 +1,8 @@
+/* [cinny #43] EC's screenshare button, floating in the frame's bottom-right
+corner while the host draws the rest of the call bar. */
+.floating {
+  position: fixed;
+  right: var(--cpd-space-4x);
+  bottom: calc(env(safe-area-inset-bottom) + var(--cpd-space-4x));
+  z-index: 1;
+}

src/lotus/LotusFrameScreenshare.test.tsx

@@ -0,0 +1,88 @@
+/*
+Copyright 2026 Lotus Guild
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { describe, expect, it, vi } from "vitest";
+import { act, render, screen } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import { TooltipProvider } from "@vector-im/compound-web";
+import { BehaviorSubject } from "rxjs";
+
+import { type CallViewModel } from "../state/CallViewModel/CallViewModel";
+import { LotusFrameScreenshare } from "./LotusFrameScreenshare";
+import {
+  lotusFrameScreenshareEnabled,
+  lotusFrameScreenshareVisible$,
+  parseFrameScreensharePayload,
+} from "./lotusControls";
+
+// lotusFlag memoizes the URL params on first read, so set them once here.
+window.history.pushState(
+  {},
+  "",
+  "/?lotusHostControls=1&lotusFrameScreenshare=1",
+);
+
+const mockVm = (
+  toggle: (() => void) | null,
+  sharing = new BehaviorSubject(false),
+): CallViewModel =>
+  ({
+    sharingScreen$: sharing,
+    toggleScreenSharing: toggle,
+  }) as unknown as CallViewModel;
+
+const renderButton = (vm: CallViewModel): void => {
+  render(
+    <TooltipProvider>
+      <LotusFrameScreenshare vm={vm} />
+    </TooltipProvider>,
+  );
+};
+
+describe("LotusFrameScreenshare", () => {
+  it("is enabled by lotusHostControls + lotusFrameScreenshare", () => {
+    expect(lotusFrameScreenshareEnabled()).toBe(true);
+  });
+
+  it("toggles the share from a click inside the frame", async () => {
+    const toggle = vi.fn();
+    renderButton(mockVm(toggle));
+    await userEvent.click(screen.getByTestId("lotus_frame_screenshare"));
+    expect(toggle).toHaveBeenCalledTimes(1);
+  });
+
+  it("follows the sharing state", () => {
+    const sharing = new BehaviorSubject(false);
+    renderButton(mockVm(vi.fn(), sharing));
+    const button = screen.getByTestId("lotus_frame_screenshare");
+    expect(button).toHaveAttribute("aria-checked", "false");
+    act(() => sharing.next(true));
+    expect(button).toHaveAttribute("aria-checked", "true");
+  });
+
+  it("hides while the host's policy forbids sharing, unless a share is live", () => {
+    const sharing = new BehaviorSubject(false);
+    act(() => lotusFrameScreenshareVisible$.next(false));
+    renderButton(mockVm(vi.fn(), sharing));
+    expect(screen.queryByTestId("lotus_frame_screenshare")).toBeNull();
+    act(() => sharing.next(true));
+    expect(screen.getByTestId("lotus_frame_screenshare")).toBeInTheDocument();
+    act(() => lotusFrameScreenshareVisible$.next(true));
+  });
+
+  it("parses the set_frame_screenshare payload", () => {
+    expect(parseFrameScreensharePayload({ visible: false })).toBe(false);
+    expect(parseFrameScreensharePayload({ visible: true })).toBe(true);
+    expect(parseFrameScreensharePayload({})).toBeUndefined();
+    expect(parseFrameScreensharePayload(null)).toBeUndefined();
+  });
+
+  it("renders nothing when screensharing is unavailable", () => {
+    renderButton(mockVm(null));
+    expect(screen.queryByTestId("lotus_frame_screenshare")).toBeNull();
+  });
+});

src/lotus/LotusFrameScreenshare.tsx

@@ -0,0 +1,41 @@
+/*
+Copyright 2026 Lotus Guild
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { type FC } from "react";
+
+import { ShareScreenButton } from "../button";
+import { type CallViewModel } from "../state/CallViewModel/CallViewModel";
+import { useBehavior } from "../useBehavior";
+import {
+  lotusFrameScreenshareEnabled,
+  lotusFrameScreenshareVisible$,
+} from "./lotusControls";
+import styles from "./LotusFrameScreenshare.module.css";
+
+/**
+ * [cinny #43] EC's screenshare button, shown inside the frame when the host
+ * can't start a share for us (`lotusFrameScreenshare`). The rest of EC's
+ * footer stays hidden behind the host's call bar.
+ */
+export const LotusFrameScreenshare: FC<{ vm: CallViewModel }> = ({ vm }) => {
+  const sharing = useBehavior(vm.sharingScreen$);
+  const visible = useBehavior(lotusFrameScreenshareVisible$);
+  if (!lotusFrameScreenshareEnabled() || !vm.toggleScreenSharing) return null;
+  // Hidden by the host's call policy, but never while a share is live: the
+  // user must still be able to stop it.
+  if (!visible && !sharing) return null;
+  return (
+    <div className={styles.floating}>
+      <ShareScreenButton
+        size="md"
+        enabled={sharing}
+        onClick={vm.toggleScreenSharing}
+        data-testid="lotus_frame_screenshare"
+      />
+    </div>
+  );
+};

src/lotus/lotusActions.test.ts

@@ -30,6 +30,9 @@ describe("LotusWidgetActions", () => {
       LotusWidgetActions.SetLayout,
       LotusWidgetActions.OpenSettings,
       LotusWidgetActions.ToggleReactions,
+      LotusWidgetActions.SetScreenshare,
+      LotusWidgetActions.SetHotkeys,
+      LotusWidgetActions.SetFrameScreenshare,
     ];
 
     expect(new Set(LOTUS_TO_WIDGET_ACTIONS)).toEqual(new Set(expectedToWidget));
@@ -51,5 +54,6 @@ describe("LotusWidgetActions", () => {
       LotusWidgetActions.ControlsState,
     );
     expect(LOTUS_TO_WIDGET_ACTIONS).not.toContain(LotusWidgetActions.MicLevel);
+    expect(LOTUS_TO_WIDGET_ACTIONS).not.toContain(LotusWidgetActions.Hotkey);
   });
 });

src/lotus/lotusActions.ts

@@ -75,7 +75,31 @@ export enum LotusWidgetActions {
   /** toWidget: toggle the reactions / raise-hand menu (cinny #43). */
   ToggleReactions = "io.lotus.toggle_reactions",
   /**
-   * fromWidget: `{ screensharing: boolean, layout: "grid" | "spotlight" | null }`
+   * toWidget: start/stop sharing `{ on?: boolean }` (omit to toggle; cinny #43).
+   * Starting calls getDisplayMedia, which needs the user's click: the host
+   * sends this with Capability Delegation (`delegate: "display-capture"`), and
+   * without it the browser rejects the share.
+   */
+  SetScreenshare = "io.lotus.set_screenshare",
+  /**
+   * toWidget: `{ codes: string[] }` — KeyboardEvent.code values (PTT, deafen)
+   * to report while focus is inside this frame (cinny #43). `[]` stops.
+   */
+  SetHotkeys = "io.lotus.set_hotkeys",
+  /**
+   * toWidget: `{ visible: boolean }` — whether the in-frame screenshare button
+   * (`lotusFrameScreenshare`) may show, e.g. false while the room's call
+   * policy forbids screensharing (cinny #43). Defaults to visible.
+   */
+  SetFrameScreenshare = "io.lotus.set_frame_screenshare",
+  /**
+   * fromWidget: a watched key went down/up here, or this window's focus
+   * changed; see `LotusHotkeyReport` (cinny #43).
+   */
+  Hotkey = "io.lotus.hotkey",
+  /**
+   * fromWidget: `{ screensharing: boolean, layout: "grid" | "spotlight" | null,
+   * screenshareAction: true, hotkeys: true, frameScreenshare: boolean }`
    * whenever either changes (cinny #43), so the host stops reading EC's DOM for
    * them. Its arrival also tells the host this fork supports the actions above.
    */
@@ -98,4 +122,7 @@ export const LOTUS_TO_WIDGET_ACTIONS: LotusWidgetActions[] = [
   LotusWidgetActions.SetLayout,
   LotusWidgetActions.OpenSettings,
   LotusWidgetActions.ToggleReactions,
+  LotusWidgetActions.SetScreenshare,
+  LotusWidgetActions.SetHotkeys,
+  LotusWidgetActions.SetFrameScreenshare,
 ];

src/lotus/lotusAudioInject.test.ts

@@ -10,7 +10,11 @@ import { afterEach, beforeEach, expect, test, vi } from "vitest";
 import { of } from "rxjs";
 
 import { type CallViewModel } from "../state/CallViewModel/CallViewModel";
-import { startLotusAudioInject } from "./lotusAudioInject";
+import {
+  MAX_INJECT_BYTES,
+  parseInjectSource,
+  startLotusAudioInject,
+} from "./lotusAudioInject";
 import { LotusWidgetActions } from "./lotusActions";
 
 const lazyActions = new EventEmitter();
@@ -223,3 +227,34 @@ test("#14: the shared context stays open while another instance is still active"
   stopB();
   expect(ctx.close).toHaveBeenCalledTimes(1);
 });
+
+// [cinny #43] Cross-origin hosts send the clip bytes instead of a blob: URL.
+test("parseInjectSource prefers the clip bytes over the url", () => {
+  const audio = new ArrayBuffer(16);
+  expect(parseInjectSource({ audio, url: "https://x.example/a.ogg" })).toBe(
+    audio,
+  );
+});
+
+test("parseInjectSource falls back to a safe url", () => {
+  expect(parseInjectSource({ url: "https://x.example/a.ogg" })).toBe(
+    "https://x.example/a.ogg",
+  );
+  expect(
+    parseInjectSource({
+      audio: new ArrayBuffer(0),
+      url: "https://x.example/a.ogg",
+    }),
+  ).toBe("https://x.example/a.ogg");
+  expect(parseInjectSource({ url: "javascript" + ":alert(1)" })).toBeNull();
+  expect(parseInjectSource({})).toBeNull();
+  expect(parseInjectSource(undefined)).toBeNull();
+});
+
+test("parseInjectSource rejects oversized or non-buffer audio", () => {
+  expect(
+    parseInjectSource({ audio: new ArrayBuffer(MAX_INJECT_BYTES + 1) }),
+  ).toBeNull();
+  expect(parseInjectSource({ audio: "not bytes" })).toBeNull();
+  expect(parseInjectSource({ audio: new Uint8Array(4) })).toBeNull();
+});

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
+ * Action data: `{ url?: string, audio?: ArrayBuffer, volume?: number }`.
- * URL (the host resolves mxc → media URL).
+ * `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;
+    const clip = parseInjectSource(data);
-    if (!url) {
+    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;
+  let arrayBuffer: ArrayBuffer;
-  try {
+  if (typeof clip !== "string") {
-    resp = await fetch(url, {
+    arrayBuffer = clip;
-      credentials: "omit",
+  } else {
-      mode: "cors",
+    let resp: Response;
-      signal: controller.signal,
+    try {
-    });
+      resp = await fetch(clip, {
-  } catch (e) {
+        credentials: "omit",
-    // Superseded by a newer clip mid-fetch — expected, not a failure.
+        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.

src/lotus/lotusControls.test.ts

@@ -7,7 +7,11 @@ Please see LICENSE in the repository root for full details.
 
 import { describe, expect, it } from "vitest";
 
-import { parseLayoutPayload, parseSettingsPayload } from "./lotusControls";
+import {
+  parseLayoutPayload,
+  parseSettingsPayload,
+  shouldToggleScreenshare,
+} from "./lotusControls";
 
 describe("parseLayoutPayload", () => {
   it("accepts grid and spotlight", () => {
@@ -33,3 +37,17 @@ describe("parseSettingsPayload", () => {
     expect(parseSettingsPayload({ open: "yes" }, true)).toBe(false);
   });
 });
+
+describe("shouldToggleScreenshare", () => {
+  it("toggles only when an explicit on differs from the current state", () => {
+    expect(shouldToggleScreenshare({ on: true }, false)).toBe(true);
+    expect(shouldToggleScreenshare({ on: true }, true)).toBe(false);
+    expect(shouldToggleScreenshare({ on: false }, true)).toBe(true);
+    expect(shouldToggleScreenshare({ on: false }, false)).toBe(false);
+  });
+  it("toggles when on is missing or not a boolean", () => {
+    expect(shouldToggleScreenshare({}, false)).toBe(true);
+    expect(shouldToggleScreenshare({ on: "yes" }, true)).toBe(true);
+    expect(shouldToggleScreenshare(null, true)).toBe(true);
+  });
+});

src/lotus/lotusControls.ts

@@ -6,13 +6,13 @@ Please see LICENSE in the repository root for full details.
 */
 
 import { type IWidgetApiRequest } from "matrix-widget-api";
-import { combineLatest, of, type Subscription } from "rxjs";
+import { BehaviorSubject, combineLatest, of, type Subscription } from "rxjs";
 import { distinctUntilChanged, map, switchMap } from "rxjs/operators";
 
 import { type CallViewModel } from "../state/CallViewModel/CallViewModel";
 import { type LayoutMode } from "../state/LayoutSwitchViewModel";
 import { widget } from "../widget";
-import { LotusWidgetActions, lotusSendToHost } from "./lotusWidget";
+import { LotusWidgetActions, lotusFlag, lotusSendToHost } from "./lotusWidget";
 
 /** Window event the reactions button listens for (see ReactionToggleButton). */
 export const LOTUS_TOGGLE_REACTIONS_EVENT = "lotus:toggle-reactions";
@@ -21,6 +21,42 @@ export interface LotusControlsState {
   screensharing: boolean;
   /** Null while EC offers no layout switch (e.g. PiP or a 1:1 layout). */
   layout: LayoutMode | null;
+  /** This fork handles `io.lotus.set_screenshare` (always true). */
+  screenshareAction: true;
+  /** This fork handles `io.lotus.set_hotkeys` (always true). */
+  hotkeys: true;
+  /**
+   * EC's own screenshare button is shown inside the frame (see
+   * `lotusFrameScreenshare`), so the host should hide its own.
+   */
+  frameScreenshare: boolean;
+}
+
+/**
+ * [cinny #43] `lotusFrameScreenshare=1` (with `lotusHostControls`): the host
+ * can't hand the user's click into this frame (no Capability Delegation:
+ * Firefox, Safari, WebKitGTK), and `getDisplayMedia` needs that click here.
+ * So EC's own screenshare button stays visible in the frame, where the click
+ * is native, instead of the host clicking it through the DOM.
+ */
+export function lotusFrameScreenshareEnabled(): boolean {
+  return lotusFlag("lotusHostControls") && lotusFlag("lotusFrameScreenshare");
+}
+
+/**
+ * Host-controlled visibility of the in-frame screenshare button
+ * (`io.lotus.set_frame_screenshare`): the host hides it while the room's
+ * call policy forbids screensharing, as it does its own call-bar button.
+ */
+export const lotusFrameScreenshareVisible$ = new BehaviorSubject(true);
+
+/** `{ visible }` payload → the visibility to apply, or undefined. Exported for tests. */
+export function parseFrameScreensharePayload(
+  data: unknown,
+): boolean | undefined {
+  if (typeof data !== "object" || data === null) return undefined;
+  const { visible } = data as { visible?: unknown };
+  return typeof visible === "boolean" ? visible : undefined;
 }
 
 /** `{ layout }` payload → a layout mode, or undefined if invalid. Exported for tests. */
@@ -39,13 +75,28 @@ export function parseSettingsPayload(data: unknown, current: boolean): boolean {
   return !current;
 }
 
+/**
+ * `{ on? }` payload + current sharing state → whether to call the toggle.
+ * Exported for tests.
+ */
+export function shouldToggleScreenshare(
+  data: unknown,
+  sharing: boolean,
+): boolean {
+  if (typeof data === "object" && data !== null && "on" in data) {
+    const { on } = data as { on?: unknown };
+    if (typeof on === "boolean") return on !== sharing;
+  }
+  return true;
+}
+
 /**
  * [cinny #43] Widget-API replacements for the host's DOM access to EC's
  * controls: layout switch, settings modal and reactions menu, plus a
  * `controls_state` report (screensharing + layout) so the host no longer reads
- * EC's DOM for them. Screensharing itself stays host-DOM driven for now:
+ * EC's DOM for them. Screenshare start/stop too: `getDisplayMedia` needs the
- * `getDisplayMedia` needs the user's click to reach this frame (Capability
+ * user's click in this frame, so the host sends `set_screenshare` with
- * Delegation), which a plain widget message doesn't carry.
+ * Capability Delegation (Chromium). Elsewhere it keeps clicking EC's button.
  *
  * No effect unless the host sends the actions; registering is safe whenever
  * we're a widget. Returns a teardown function.
@@ -69,10 +120,29 @@ export function startLotusControls(vm: CallViewModel): () => void {
     w.api.transport.reply(ev.detail, {});
     window.dispatchEvent(new Event(LOTUS_TOGGLE_REACTIONS_EVENT));
   };
+  const onSetScreenshare = (ev: CustomEvent<IWidgetApiRequest>): void => {
+    w.api.transport.reply(ev.detail, {});
+    // Call synchronously: the delegated activation is only good for a few
+    // seconds after the message arrived.
+    if (shouldToggleScreenshare(ev.detail.data, vm.sharingScreen$.value)) {
+      vm.toggleScreenSharing?.();
+    }
+  };
 
   w.lazyActions.on(LotusWidgetActions.SetLayout, onSetLayout);
   w.lazyActions.on(LotusWidgetActions.OpenSettings, onOpenSettings);
   w.lazyActions.on(LotusWidgetActions.ToggleReactions, onToggleReactions);
+  const onSetFrameScreenshare = (ev: CustomEvent<IWidgetApiRequest>): void => {
+    w.api.transport.reply(ev.detail, {});
+    const visible = parseFrameScreensharePayload(ev.detail.data);
+    if (visible !== undefined) lotusFrameScreenshareVisible$.next(visible);
+  };
+
+  w.lazyActions.on(LotusWidgetActions.SetScreenshare, onSetScreenshare);
+  w.lazyActions.on(
+    LotusWidgetActions.SetFrameScreenshare,
+    onSetFrameScreenshare,
+  );
 
   const sub: Subscription = combineLatest([
     vm.sharingScreen$,
@@ -85,6 +155,9 @@ export function startLotusControls(vm: CallViewModel): () => void {
         ([screensharing, layout]): LotusControlsState => ({
           screensharing,
           layout,
+          screenshareAction: true,
+          hotkeys: true,
+          frameScreenshare: lotusFrameScreenshareEnabled(),
         }),
       ),
       distinctUntilChanged(
@@ -100,5 +173,10 @@ export function startLotusControls(vm: CallViewModel): () => void {
     w.lazyActions.off(LotusWidgetActions.SetLayout, onSetLayout);
     w.lazyActions.off(LotusWidgetActions.OpenSettings, onOpenSettings);
     w.lazyActions.off(LotusWidgetActions.ToggleReactions, onToggleReactions);
+    w.lazyActions.off(LotusWidgetActions.SetScreenshare, onSetScreenshare);
+    w.lazyActions.off(
+      LotusWidgetActions.SetFrameScreenshare,
+      onSetFrameScreenshare,
+    );
   };
 }

src/lotus/lotusHotkeys.test.ts

@@ -0,0 +1,50 @@
+/*
+Copyright 2026 Lotus Guild
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { describe, expect, it } from "vitest";
+
+import {
+  isEditableTarget,
+  isInteractiveTarget,
+  parseHotkeyCodes,
+} from "./lotusHotkeys";
+
+describe("parseHotkeyCodes", () => {
+  it("keeps KeyboardEvent.code-like strings", () => {
+    expect(parseHotkeyCodes({ codes: ["Space", "KeyM", "F13"] })).toEqual([
+      "Space",
+      "KeyM",
+      "F13",
+    ]);
+  });
+  it("drops junk and caps the list", () => {
+    expect(parseHotkeyCodes({ codes: ["Space", 3, "", "a b", "<x>"] })).toEqual(
+      ["Space"],
+    );
+    expect(parseHotkeyCodes({ codes: Array(20).fill("KeyA") })).toHaveLength(8);
+    expect(parseHotkeyCodes({})).toEqual([]);
+    expect(parseHotkeyCodes(null)).toEqual([]);
+  });
+});
+
+describe("target checks", () => {
+  it("treats inputs and contenteditable as editable", () => {
+    document.body.innerHTML =
+      '<input id="i"><div contenteditable="true"><span id="s">x</span></div><div id="d"></div>';
+    expect(isEditableTarget(document.getElementById("i"))).toBe(true);
+    expect(isEditableTarget(document.getElementById("s"))).toBe(true);
+    expect(isEditableTarget(document.getElementById("d"))).toBe(false);
+    expect(isEditableTarget(null)).toBe(false);
+  });
+  it("treats buttons, links and button roles as interactive", () => {
+    document.body.innerHTML =
+      '<button id="b">b</button><div role="menuitem"><span id="m">m</span></div><p id="p"></p>';
+    expect(isInteractiveTarget(document.getElementById("b"))).toBe(true);
+    expect(isInteractiveTarget(document.getElementById("m"))).toBe(true);
+    expect(isInteractiveTarget(document.getElementById("p"))).toBe(false);
+  });
+});

src/lotus/lotusHotkeys.ts

@@ -0,0 +1,159 @@
+/*
+Copyright 2026 Lotus Guild
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { type IWidgetApiRequest } from "matrix-widget-api";
+
+import { widget } from "../widget";
+import { LotusWidgetActions, lotusSendToHost } from "./lotusWidget";
+
+/** fromWidget `io.lotus.hotkey` payload. */
+export type LotusHotkeyReport =
+  | {
+      type: "keydown" | "keyup";
+      code: string;
+      repeat: boolean;
+      ctrlKey: boolean;
+      altKey: boolean;
+      metaKey: boolean;
+      shiftKey: boolean;
+      /** The key went to a text field (typing, not a hotkey). */
+      editable: boolean;
+      /** The key went to a button/link/etc. (Space activates it). */
+      interactive: boolean;
+    }
+  /** This window gained or lost focus: the host releases a held PTT. */
+  | { type: "focus" };
+
+const MAX_CODES = 8;
+
+// Codes the host currently owns. Module-level so EC's own shortcuts
+// (useCallViewKeyboardShortcuts) can stand down for them.
+let hostCodes = new Set<string>();
+
+/**
+ * Whether `code` is one of the host's call hotkeys (its PTT or deafen key).
+ * EC's built-in shortcuts ignore such keys: with the defaults, M would
+ * otherwise both toggle EC's mic and the host's deafen, and Space would open
+ * EC's own push-to-talk alongside the host's.
+ */
+export function isLotusHostHotkey(code: string): boolean {
+  return hostCodes.has(code);
+}
+
+/** `{ codes }` payload → the KeyboardEvent.code values to watch. Exported for tests. */
+export function parseHotkeyCodes(data: unknown): string[] {
+  if (typeof data !== "object" || data === null) return [];
+  const { codes } = data as { codes?: unknown };
+  if (!Array.isArray(codes)) return [];
+  return codes
+    .filter(
+      (c): c is string =>
+        typeof c === "string" && /^[A-Za-z0-9]{1,32}$/.test(c),
+    )
+    .slice(0, MAX_CODES);
+}
+
+/** Same rules as the host's useCallHotkeys. Exported for tests. */
+export function isEditableTarget(el: Element | null): boolean {
+  if (!(el instanceof HTMLElement)) return false;
+  const tag = el.tagName;
+  if (tag === "INPUT" || tag === "TEXTAREA" || tag === "SELECT") return true;
+  let node: HTMLElement | null = el;
+  while (node && node !== el.ownerDocument.body) {
+    const ce = node.getAttribute("contenteditable");
+    if (ce === "" || ce === "true" || ce === "plaintext-only") return true;
+    if (ce === "false") return false;
+    node = node.parentElement;
+  }
+  return false;
+}
+
+/** Exported for tests. */
+export function isInteractiveTarget(el: Element | null): boolean {
+  if (!(el instanceof HTMLElement)) return false;
+  const tag = el.tagName;
+  if (tag === "BUTTON" || tag === "A" || tag === "SELECT") return true;
+  let node: HTMLElement | null = el;
+  while (node && node !== el.ownerDocument.body) {
+    const role = node.getAttribute("role");
+    if (
+      role === "button" ||
+      role === "link" ||
+      role === "menuitem" ||
+      role === "tab"
+    )
+      return true;
+    node = node.parentElement;
+  }
+  return false;
+}
+
+/**
+ * [cinny #43] Call hotkeys (push-to-talk, deafen) while focus is inside this
+ * frame. The host used to add key listeners to this window directly, which
+ * needs same-origin access. Now it sends `io.lotus.set_hotkeys { codes }` and
+ * we report those keys back as `io.lotus.hotkey`. The default action is
+ * cancelled here, synchronously (it can't be across frames), with the host's
+ * rules: never while typing in a field, and not on a focused button/link so
+ * keyboard users can still activate it. Returns a teardown function.
+ */
+export function startLotusHotkeys(): () => void {
+  const w = widget;
+  if (!w) return (): void => undefined;
+  hostCodes = new Set<string>();
+
+  const onSetHotkeys = (ev: CustomEvent<IWidgetApiRequest>): void => {
+    w.api.transport.reply(ev.detail, {});
+    hostCodes = new Set(parseHotkeyCodes(ev.detail.data));
+  };
+  const onKey = (e: KeyboardEvent): void => {
+    if (!hostCodes.has(e.code)) return;
+    const target = e.target instanceof Element ? e.target : null;
+    const editable = isEditableTarget(target);
+    const interactive = isInteractiveTarget(target);
+    if (
+      e.type === "keydown" &&
+      !editable &&
+      !interactive &&
+      !e.ctrlKey &&
+      !e.altKey &&
+      !e.metaKey
+    ) {
+      e.preventDefault();
+    }
+    const report: LotusHotkeyReport = {
+      type: e.type === "keyup" ? "keyup" : "keydown",
+      code: e.code,
+      repeat: e.repeat,
+      ctrlKey: e.ctrlKey,
+      altKey: e.altKey,
+      metaKey: e.metaKey,
+      shiftKey: e.shiftKey,
+      editable,
+      interactive,
+    };
+    lotusSendToHost(LotusWidgetActions.Hotkey, report);
+  };
+  const onFocusChange = (): void => {
+    if (hostCodes.size > 0)
+      lotusSendToHost(LotusWidgetActions.Hotkey, { type: "focus" });
+  };
+
+  w.lazyActions.on(LotusWidgetActions.SetHotkeys, onSetHotkeys);
+  window.addEventListener("keydown", onKey, true);
+  window.addEventListener("keyup", onKey, true);
+  window.addEventListener("blur", onFocusChange);
+  window.addEventListener("focus", onFocusChange);
+  return (): void => {
+    w.lazyActions.off(LotusWidgetActions.SetHotkeys, onSetHotkeys);
+    window.removeEventListener("keydown", onKey, true);
+    window.removeEventListener("keyup", onKey, true);
+    window.removeEventListener("blur", onFocusChange);
+    window.removeEventListener("focus", onFocusChange);
+    hostCodes = new Set<string>();
+  };
+}

src/lotus/lotusWidgetOrigin.test.ts

@@ -0,0 +1,65 @@
+/*
+Copyright 2026 Lotus Guild
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { describe, expect, it } from "vitest";
+
+import { isFromHost, restrictToHost } from "./lotusWidgetOrigin";
+
+const parent = {} as Window;
+const other = {} as Window;
+const HOST = "https://chat.example.org";
+
+describe("isFromHost", () => {
+  it("accepts only the parent window at the host origin", () => {
+    expect(isFromHost({ source: parent, origin: HOST }, parent, HOST)).toBe(
+      true,
+    );
+    expect(isFromHost({ source: other, origin: HOST }, parent, HOST)).toBe(
+      false,
+    );
+    expect(
+      isFromHost(
+        { source: parent, origin: "https://evil.example" },
+        parent,
+        HOST,
+      ),
+    ).toBe(false);
+    expect(isFromHost({ source: parent, origin: "null" }, parent, HOST)).toBe(
+      false,
+    );
+  });
+});
+
+describe("restrictToHost", () => {
+  it("replaces the listener and drops foreign messages", () => {
+    const seen: unknown[] = [];
+    const original = (ev: MessageEvent): void => {
+      seen.push(ev.data);
+    };
+    const transport = { handleMessage: original };
+    const listeners = new Set<EventListener>([original as EventListener]);
+    const inbound = {
+      addEventListener: (_t: string, l: EventListener): void => {
+        listeners.add(l);
+      },
+      removeEventListener: (_t: string, l: EventListener): void => {
+        listeners.delete(l);
+      },
+    } as unknown as Window;
+
+    restrictToHost(transport, HOST, parent, inbound);
+    expect(listeners.has(original as EventListener)).toBe(false);
+    expect(listeners.size).toBe(1);
+
+    const dispatch = (ev: Partial<MessageEvent>): void =>
+      listeners.forEach((l) => l(ev as unknown as Event));
+    dispatch({ source: other, origin: HOST, data: "spoof" });
+    dispatch({ source: parent, origin: "https://evil.example", data: "bad" });
+    dispatch({ source: parent, origin: HOST, data: "real" });
+    expect(seen).toEqual(["real"]);
+  });
+});

src/lotus/lotusWidgetOrigin.ts

@@ -0,0 +1,53 @@
+/*
+Copyright 2026 Lotus Guild
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+type MessageLike = Pick<MessageEvent, "source" | "origin">;
+
+/** True when a message came from our parent window, at the host's origin. */
+export function isFromHost(
+  ev: MessageLike,
+  parentWindow: Window,
+  parentOrigin: string,
+): boolean {
+  return ev.source === parentWindow && ev.origin === parentOrigin;
+}
+
+interface InboundTransport {
+  handleMessage: (ev: MessageEvent) => void;
+}
+
+/**
+ * [cinny #43] Only handle widget messages sent by the host (our parent window)
+ * from the origin it was loaded at (`parentUrl`).
+ *
+ * matrix-widget-api's `strictOriginCheck` compares `ev.origin` with this
+ * frame's OWN origin, which only works while EC is served from the host's
+ * origin; served from its own origin (e.g. call.chat.lotusguild.org) every
+ * host message would be dropped. Turning the check off instead would let any
+ * window post toWidget actions (including io.lotus.*). This compares against
+ * the host's origin and also requires the sender to be our parent, so it is
+ * correct same-origin and cross-origin alike.
+ *
+ * Swaps the transport's `message` listener; safe whether or not the transport
+ * has started (`stop()` removes `handleMessage`, the guarded one after this).
+ */
+export function restrictToHost(
+  transport: unknown,
+  parentOrigin: string,
+  parentWindow: Window = window.parent,
+  inbound: Pick<Window, "addEventListener" | "removeEventListener"> = window,
+): void {
+  const t = transport as InboundTransport;
+  const original = t.handleMessage;
+  const guarded = (ev: MessageEvent): void => {
+    if (!isFromHost(ev, parentWindow, parentOrigin)) return;
+    original(ev);
+  };
+  inbound.removeEventListener("message", original as EventListener);
+  t.handleMessage = guarded;
+  inbound.addEventListener("message", guarded as EventListener);
+}

src/room/InCallView.tsx

@@ -32,6 +32,8 @@ import { widget } from "../widget";
 import { startLotusCallState } from "../lotus/lotusCallState";
 import { startLotusFocus } from "../lotus/lotusFocus";
 import { startLotusControls } from "../lotus/lotusControls";
+import { startLotusHotkeys } from "../lotus/lotusHotkeys";
+import { LotusFrameScreenshare } from "../lotus/LotusFrameScreenshare";
 import { startLotusMicLevel } from "../lotus/lotusMicLevel";
 import { startLotusAudioInject } from "../lotus/lotusAudioInject";
 import { startLotusQuality } from "../lotus/lotusQuality";
@@ -305,6 +307,7 @@ export const InCallView: FC<InCallViewProps> = ({
   // [cinny #43] layout / settings / reactions over the widget API, plus a
   // screensharing + layout report, replacing the host's DOM access.
   useEffect(() => startLotusControls(vm), [vm]);
+  useEffect(() => startLotusHotkeys(), []);
   // [cinny #146] Local mic level for the host's mute-button meter.
   useEffect(() => startLotusMicLevel(vm), [vm]);
   // [lotus] Handle the host's io.lotus.inject_audio action to mix a soundboard
@@ -690,6 +693,7 @@ export const InCallView: FC<InCallViewProps> = ({
       {earpieceOverlay}
       <ReactionsOverlay vm={vm} />
       {footer}
+      <LotusFrameScreenshare vm={vm} />
       {showModals && (
         <>
           <RageshakeRequestModal {...rageshakeRequestModalProps} />

src/useCallViewKeyboardShortcuts.ts

@@ -14,6 +14,7 @@ import {
   ReactionSet,
   ReactionsRowSize,
 } from "./reactions";
+import { isLotusHostHotkey } from "./lotus/lotusHotkeys";
 
 /**
  * Determines whether focus is in the same part of the tree as the given
@@ -86,6 +87,8 @@ export function useCallViewKeyboardShortcuts(
     useCallback(
       (event: KeyboardEvent) => {
         logger.info("Keydown event", event);
+        // [lotus] The Lotus host owns its PTT / deafen keys (cinny #43).
+        if (isLotusHostHotkey(event.code)) return;
         if (!mayReceiveKeyEvents()) return;
         if (event.altKey || event.ctrlKey || event.metaKey || event.shiftKey)
           return;
@@ -132,6 +135,7 @@ export function useCallViewKeyboardShortcuts(
     "keyup",
     useCallback(
       (event: KeyboardEvent) => {
+        if (isLotusHostHotkey(event.code)) return;
         if (!mayReceiveKeyEvents() || !mayReceiveSpaceKeyEvents()) return;
         if (event.key === " ") {
           spacebarHeld.current = false;

src/useTheme.ts

@@ -76,7 +76,17 @@ export const useTheme = (): void => {
           "lotusTheme anyway since the two flags are only meaningful together.",
       );
     }
-    if (lotusTheme || lotusTransparent)
+    if (lotusTheme || lotusTransparent) {
       document.body.classList.add("lotus-theme");
+      // [cinny #43] The frame's root colour scheme must match the host's, or
+      // the browser paints an opaque backdrop behind the transparent frame.
+      // (The host used to inject `:root { color-scheme }` for this.)
+      document.documentElement.style.colorScheme = theme;
+    }
+    // [cinny #43] The host draws its own call bar: hide EC's footer. Replaces
+    // the host's injected styles. Where the host can't start a share for us,
+    // LotusFrameScreenshare shows EC's screenshare button on its own.
+    if (lotusFlag("lotusHostControls"))
+      document.body.classList.add("lotus-host-controls");
   }, [previousTheme, requestedTheme]);
 };

src/widget.ts

@@ -24,6 +24,7 @@ import { Config } from "./config/Config";
 import { seedSettingsFromConfig } from "./settings/settings";
 import { ElementCallReactionEventType } from "./reactions";
 import { LOTUS_TO_WIDGET_ACTIONS } from "./lotus/lotusActions";
+import { restrictToHost } from "./lotus/lotusWidgetOrigin";
 
 // Subset of the actions in element-web
 export enum ElementWidgetActions {
@@ -94,16 +95,11 @@ export const initializeWidget = (
       const parentOrigin = new URL(parentUrl).origin;
       logger.info("Widget API is available");
       const api = new WidgetApi(widgetId, parentOrigin);
-      // [lotus] matrix-widget-api's PostmessageTransport defaults
+      // [lotus] Only messages from the host (our parent, at parentUrl's
-      // strictOriginCheck to false, which would let any frame holding a
+      // origin) reach the widget API. matrix-widget-api's own
-      // handle to our window post toWidget actions (including the
+      // strictOriginCheck compares against THIS frame's origin, so it only
-      // io.lotus.* actions below). The Lotus deployment serves EC
+      // worked while EC was served from the host's origin (cinny #43).
-      // same-origin with the host (cinny loads /public/element-call/index.html),
+      restrictToHost(api.transport, parentOrigin);
-      // so globalThis.origin === parentOrigin and this check passes safely.
-      // A cross-origin deployment would need to compare ev.origin to
-      // parentOrigin instead, since strictOriginCheck compares against
-      // globalThis.origin.
-      api.transport.strictOriginCheck = true;
       api.requestCapability(MatrixCapabilities.AlwaysOnScreen);
       api.requestCapability(MatrixCapabilities.MSC4039DownloadFile);