fix(tts): avoid race condition in preloadNextSSML causing wrong highlights (#3748)

preloadNextSSML() called tts.next() interleaved with await, creating async
gaps where the concurrent #speak() could dispatch marks against corrupted
#ranges state (replaced by next() for a different block). Since mark names
restart at "0" per block, marks resolved to the wrong text position, causing
accidental page turns and highlights far from the current sentence.

Fix: gather all tts.next() and tts.prev() calls synchronously (no await
between them) so no async code can see the intermediate #ranges state.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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

@@ -261,15 +261,27 @@ export class TTSController extends EventTarget {
     const tts = this.view.tts;
     if (!tts) return;
 
-    const ssmls: string[] = [];
+    // Gather all next SSMLs and rewind synchronously to avoid a race condition:
+    // tts.next() replaces TTS.#ranges (used by setMark() during playback).
+    // If async gaps exist between next()/prev() calls, a concurrent #speak()
+    // can dispatch marks against the wrong #ranges, causing incorrect highlights
+    // and accidental page turns.
+    const rawSsmls: string[] = [];
     for (let i = 0; i < count; i++) {
-      const ssml = await this.#preprocessSSML(tts.next());
+      const ssml = tts.next();
+      if (!ssml) break;
+      rawSsmls.push(ssml);
+    }
+    for (let i = 0; i < rawSsmls.length; i++) {
+      tts.prev();
+    }
+
+    const ssmls: string[] = [];
+    for (const raw of rawSsmls) {
+      const ssml = await this.#preprocessSSML(raw);
       if (!ssml) break;
       ssmls.push(ssml);
     }
-    for (let i = 0; i < ssmls.length; i++) {
-      tts.prev();
-    }
     await Promise.all(ssmls.map((ssml) => this.preloadSSML(ssml, new AbortController().signal)));
   }