fix(lotus): denoise restart fallback must not hand LiveKit its own raw track

On a failed restart() the processor set processedTrack to the LiveKit-owned
input track. LiveKit's internalStopProcessor() stops processedTrack and then
republishes _mediaStreamTrack — the same object — so any later
stopProcessor()/teardown killed the live mic for the rest of the session.
Leave processedTrack undefined so LiveKit falls through to its own track.
Unit-tested.

Fixes #2

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/lotus/lotusDenoiseProcessor.test.ts

@@ -0,0 +1,55 @@
+/*
+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, test } from "vitest";
+import { type AudioProcessorOptions } from "livekit-client";
+
+import { LotusDenoiseProcessor } from "./lotusDenoiseProcessor";
+
+function makeProcessor(): LotusDenoiseProcessor {
+  return new LotusDenoiseProcessor({
+    model: "rnnoise",
+    assetBase: "https://example.invalid/denoise/",
+    gate: false,
+    gateThreshold: -45,
+    floor: 0.15,
+  });
+}
+
+describe("LotusDenoiseProcessor.restart", () => {
+  test("falls back to processedTrack = undefined (never the raw LiveKit track) when graph rebuild fails", async () => {
+    const processor = makeProcessor();
+
+    // Stub out the AudioContext/graph plumbing: pretend the context is fine
+    // but the graph rebuild (wasm load / worklet construction) throws, which
+    // is the path this test targets.
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    (processor as any).ensureContext = async (): Promise<void> => {
+      await Promise.resolve();
+    };
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    (processor as any).buildGraph = async (): Promise<never> => {
+      await Promise.resolve();
+      throw new Error("simulated graph build failure");
+    };
+
+    const rawTrack = {
+      stop: (): void => undefined,
+    } as unknown as MediaStreamTrack;
+
+    await processor.restart({
+      track: rawTrack,
+    } as unknown as AudioProcessorOptions);
+
+    // Must NOT be the raw, LiveKit-owned track: LiveKit's
+    // internalStopProcessor() calls `processor.processedTrack?.stop()` then
+    // re-publishes the same `_mediaStreamTrack` object, which would kill the
+    // live mic on the next stopProcessor()/teardown if we handed it back here.
+    expect(processor.processedTrack).toBeUndefined();
+    expect(processor.processedTrack).not.toBe(rawTrack);
+  });
+});