Offer background effects on any platform whose browser can run them

- The desktop rule from #4059 goes: now that the menu says where effects
  run slowly, using them there is the user's choice. A phone on the fast
  route held 99% of its frame rate and was refused; a desktop on the slow
  one held 73% and was allowed.
- Asks @livekit/track-processors directly; the wrapper module goes.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/components/CallFooterViewModel.test.ts

@@ -250,12 +250,12 @@ describe("createCallFooterViewModel", () => {
       );
     }
 
-    it("offers nothing on a phone, where the pipeline would refuse them", () => {
+    it("offers them on a phone whose browser can run them", () => {
       sdkSupportMock.mockReturnValue(true);
-      expect(lobbyOn("ios").selectBackgroundEffect$.value).toBeUndefined();
+      expect(lobbyOn("ios").selectBackgroundEffect$.value).toBeDefined();
     });
 
-    it("offers them where the pipeline will honour them", () => {
+    it("offers them on a desktop whose browser can run them", () => {
       sdkSupportMock.mockReturnValue(true);
       expect(lobbyOn("desktop").selectBackgroundEffect$.value).toBeDefined();
     });

src/components/CallFooterViewModel.tsx

@@ -13,11 +13,11 @@ import {
   switchMap,
 } from "rxjs";
 import { supportsAudioOutputSelection } from "livekit-client";
-
 import {
   supportsBackgroundProcessors,
-  usesFallbackProcessing,
-} from "../tracks/backgroundProcessing";
+  supportsModernBackgroundProcessors,
+} from "@livekit/track-processors";
+
 import {
   parseEffect,
   serializeEffect,
@@ -113,7 +113,7 @@ function buildDeviceBehaviors(
     );
 
   const supported = supportsBackgroundProcessors();
-  const slow = usesFallbackProcessing();
+  const slow = !supportsModernBackgroundProcessors();
   const offered$ = disableSwitcher$.pipe(
     map((switcherDisabled) => !switcherDisabled && supported),
   );

src/tracks/BackgroundEffectsContext.test.ts

@@ -93,13 +93,13 @@ describe("BackgroundEffectsProvider", () => {
     expect(latest().processor).toBeDefined();
   });
 
-  it("does not run on a phone, even where its browser could", async () => {
+  it("runs on a phone whose browser can run it", async () => {
     platformMock.platform = "ios";
     render(surface());
     await blur(true);
 
-    expect(latest().supported).toBe(false);
-    expect(latest().processor).toBeUndefined();
+    expect(latest().supported).toBe(true);
+    expect(latest().processor).toBeDefined();
   });
 
   it("switches to an effect chosen while the camera is off", async () => {

src/tracks/BackgroundEffectsContext.tsx

@@ -5,12 +5,14 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { BackgroundProcessorWrapper } from "@livekit/track-processors";
+import {
+  BackgroundProcessorWrapper,
+  supportsBackgroundProcessors,
+} from "@livekit/track-processors";
 import { createContext, type FC, type JSX, use } from "react";
 
 import { backgroundEffect as backgroundEffectSetting } from "../settings/settings";
 import { BackgroundEffectTransformer } from "./BackgroundEffectTransformer";
-import { supportsBackgroundProcessors } from "./backgroundProcessing";
 import { type Behavior } from "../state/Behavior";
 import { type ObservableScope } from "../state/ObservableScope";
 import {

src/tracks/backgroundProcessing.ts

@@ -1,27 +0,0 @@
-/*
-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 {
-  supportsBackgroundProcessors as supportsBackgroundProcessorsLivekitSdk,
-  supportsModernBackgroundProcessors,
-} from "@livekit/track-processors";
-
-import { platform } from "../Platform";
-
-/** One answer for the controls and the pipeline, so neither offers what the other refuses. */
-export function supportsBackgroundProcessors(): boolean {
-  return supportsBackgroundProcessorsLivekitSdk() && platform === "desktop";
-}
-
-/**
- * Whether effects, where they run at all, draw every frame through a canvas:
- * the slower route, which costs frame rate and stalls the page while the
- * first one is built.
- */
-export function usesFallbackProcessing(): boolean {
-  return !supportsModernBackgroundProcessors();
-}