Tidy the background effect pipeline after review

- The Vite transform wrapper takes Vite's own types, with no cast.
- The pipeline's options are compared with deepCompare, not as JSON.
- Renames `attached` to `enable` and shortens the pipeline's doc comment.
- Drops a comment that blamed an ended track on the pipeline's queue.

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

src/livekit/TrackProcessorContext.tsx

@@ -76,8 +76,6 @@ export function applyProcessor(
     }
     const track = videoTrack.mediaStreamTrack;
     videoTrack.setProcessor(processor).catch((e) => {
-      // The pipeline builds one track at a time, so a track can end while its
-      // build waits a turn. The camera's next track attaches it again.
       if (track.readyState === "ended")
         logger.debug("Video processor not attached: the track ended first");
       else logger.warn("Failed to attach video processor", e);

src/state/BackgroundEffects.ts

@@ -11,6 +11,7 @@ import {
   type SwitchBackgroundProcessorOptions,
 } from "@livekit/track-processors";
 import { logger } from "matrix-js-sdk/lib/logger";
+import { deepCompare } from "matrix-js-sdk/lib/utils";
 
 import { type Behavior } from "./Behavior";
 import { type ObservableScope } from "./ObservableScope";
@@ -23,11 +24,7 @@ export interface BackgroundEffectsOptions {
   supported: boolean;
   /** Whether blur is chosen. */
   blur$: Behavior<boolean>;
-  /**
-   * Shared by the pre-join preview and the call. Building or destroying it is
-   * what primes it, and a primed pipeline lets its next frame through
-   * untouched, so it is switched rather than rebuilt.
-   */
+  /** The background processor pipeline to be switched between effects. */
   pipeline: BackgroundProcessorWrapper;
 }
 
@@ -45,9 +42,9 @@ export class BackgroundEffects {
           (previous, wanted) => {
             // Attached the first time an effect is wanted and never detached
             // after, so someone who never turns one on pays for none of it.
-            const attached =
+            const enable =
               previous.processor !== undefined || (supported && wanted);
-            return { supported, processor: attached ? pipeline : undefined };
+            return { supported, processor: enable ? pipeline : undefined };
           },
           { supported, processor: undefined },
         ),
@@ -61,7 +58,7 @@ export class BackgroundEffects {
         map(([, blur]): SwitchBackgroundProcessorOptions =>
           blur ? { mode: "background-blur", blurRadius } : { mode: "disabled" },
         ),
-        distinctUntilChanged((a, b) => JSON.stringify(a) === JSON.stringify(b)),
+        distinctUntilChanged(deepCompare),
         scope.bind(),
       )
       .subscribe((options) => {