fix(tts): preserve state on AbortError to keep rate changes effective on iOS, closes #3949 (#3988)

iOS WKWebView's in-flight audio.play() rejects with AbortError after audio.src is reset
during a stop+restart cycle. That rejection leaks through one of the .catch chains into
TTSController.error(), which unconditionally flipped state to 'stopped' — desyncing the
state machine so subsequent rate changes fell into the no-op else branch and #speak's
auto-forward gate stopped firing at paragraph end.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/readest-app/src/__tests__/services/tts-controller.test.ts

@@ -473,6 +473,27 @@ describe('TTSController', () => {
       expect(controller.state).toBe('stopped');
     });
 
+    test('error preserves state for AbortError (DOMException-style)', () => {
+      // iOS audio.play() and AbortSignal-aware fetches reject with a DOMException
+      // whose name is 'AbortError'. Treating it as a real error desyncs the state
+      // machine: subsequent rate changes see state !== 'playing' and skip the
+      // stop+start cycle, and #speak's auto-forward gate fails.
+      controller.state = 'playing';
+      const abort = new Error('The operation was aborted.');
+      abort.name = 'AbortError';
+      controller.error(abort);
+      expect(controller.state).toBe('playing');
+    });
+
+    test('error preserves state for our internal Aborted message', () => {
+      // EdgeTTSClient and NativeTTSClient resolve the inner promise with
+      // { code: 'error', message: 'Aborted' } on signal abort; if that bubbles
+      // through any catch path it must not flip state to 'stopped'.
+      controller.state = 'playing';
+      controller.error(new Error('Aborted'));
+      expect(controller.state).toBe('playing');
+    });
+
     test('play calls start when not playing', () => {
       controller.state = 'stopped';
       const startSpy = vi.spyOn(controller, 'start').mockResolvedValue();

apps/readest-app/src/services/tts/TTSController.ts

@@ -558,6 +558,16 @@ export class TTSController extends EventTarget {
   }
 
   error(e: unknown) {
+    // AbortError is expected during normal stop/restart cycles (rate change,
+    // forward/backward, voice change) — on iOS especially, the in-flight
+    // audio.play() promise rejects with AbortError after audio.src is reset,
+    // and that rejection can leak through one of the .catch chains. Letting it
+    // flip state to 'stopped' desyncs the state machine: handleSetRate's
+    // `state === 'playing'` check then falls through to a no-op, and #speak's
+    // auto-forward gate skips advancing to the next paragraph.
+    if (e instanceof Error && (e.name === 'AbortError' || e.message === 'Aborted')) {
+      return;
+    }
     console.error(e);
     this.state = 'stopped';
   }