fix(tts): guard SpeechSynthesisUtterance addEventListener calls

apps/web/src/features/text-to-speech/use-tts.ts

@@ -30,13 +30,28 @@ export function useTts(text: string) {
       }
     });
 
-    utterance.addEventListener("start", () => setHasStarted(true));
-    utterance.addEventListener("end", () => setHasStarted(false));
-    utterance.addEventListener("pause", () => setHasPaused(true));
-    utterance.addEventListener("resume", () => setHasPaused(false));
+    // The failing field environment is NOT an old browser: ECENCY-NEXT-1GNS
+    // fired on Chrome 138, where the real constructor is always an EventTarget.
+    // Privacy shims replace `SpeechSynthesisUtterance` with a plain object to
+    // block voice fingerprinting (same family as the iOS Brave `getVoices`
+    // shim, ECENCY-NEXT-1GMR), so nothing about the instance can be assumed.
+    if (typeof utterance.addEventListener === "function") {
+      utterance.addEventListener("start", () => setHasStarted(true));
+      utterance.addEventListener("end", () => setHasStarted(false));
+      utterance.addEventListener("pause", () => setHasPaused(true));
+      utterance.addEventListener("resume", () => setHasPaused(false));
+    } else {
+      utterance.onstart = () => setHasStarted(true);
+      utterance.onend = () => setHasStarted(false);
+      utterance.onpause = () => setHasPaused(true);
+      utterance.onresume = () => setHasPaused(false);
+    }
 
     return () => {
-      speechSynthesis.cancel();
+      // Same hostile environments: `createUtterance` only proves the
+      // constructor exists, not the manager global, and the bare identifier
+      // is a ReferenceError where `speechSynthesis` is absent entirely.
+      window.speechSynthesis?.cancel?.();
       speechRef.current = undefined;
     };
   }, [text, voice]);

apps/web/src/specs/features/text-to-speech/use-tts.spec.tsx

@@ -0,0 +1,65 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { act, renderHook } from "@testing-library/react";
+
+// A privacy shim replaces `SpeechSynthesisUtterance` with a plain object, so
+// the instance is not an EventTarget (ECENCY-NEXT-1GNS fired on Chrome 138,
+// not an old browser). The mock lets each case hand the hook whichever
+// utterance shape it wants.
+const createUtteranceMock = vi.fn();
+vi.mock("@/utils", () => ({
+  createUtterance: (text: string) => createUtteranceMock(text),
+  getVoicesAsync: vi.fn(() => new Promise(() => {})),
+  useSynchronizedLocalStorage: vi.fn(() => [undefined, vi.fn()])
+}));
+
+import { useTts } from "@/features/text-to-speech/use-tts";
+
+describe("useTts", () => {
+  beforeEach(() => {
+    createUtteranceMock.mockReset();
+  });
+
+  it("registers listeners via addEventListener when the utterance is an EventTarget", () => {
+    const addEventListener = vi.fn();
+    createUtteranceMock.mockReturnValue({ addEventListener });
+
+    renderHook(() => useTts("hello"));
+
+    expect(addEventListener.mock.calls.map(([event]) => event)).toEqual([
+      "start",
+      "end",
+      "pause",
+      "resume"
+    ]);
+  });
+
+  it("falls back to on* handlers on a shimmed utterance without crashing", () => {
+    const shim: Record<string, unknown> = {};
+    createUtteranceMock.mockReturnValue(shim);
+
+    const { result } = renderHook(() => useTts("hello"));
+
+    // The fallback wires the legacy handler properties, and they drive the
+    // same state the listeners would.
+    expect(typeof shim.onstart).toBe("function");
+    expect(typeof shim.onend).toBe("function");
+    expect(typeof shim.onpause).toBe("function");
+    expect(typeof shim.onresume).toBe("function");
+
+    act(() => (shim.onstart as () => void)());
+    expect(result.current.hasStarted).toBe(true);
+    act(() => (shim.onpause as () => void)());
+    expect(result.current.hasPaused).toBe(true);
+  });
+
+  it("survives cleanup when the speechSynthesis global is absent", () => {
+    // jsdom has no `speechSynthesis`, matching the shim environments where the
+    // constructor exists but the manager global does not — a bare-identifier
+    // `speechSynthesis.cancel()` in the effect cleanup is a ReferenceError here.
+    expect("speechSynthesis" in window).toBe(false);
+    createUtteranceMock.mockReturnValue({ addEventListener: vi.fn() });
+
+    const { unmount } = renderHook(() => useTts("hello"));
+    expect(() => unmount()).not.toThrow();
+  });
+});