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>
Huang Xin
21795e5cd3