Concurrency-limited Queue Pattern

When generating per-slide audio, run tasks in parallel but cap active requests by model rate limits.

Dynamic Concurrency

• gemini-2.5-pro-preview-tts: concurrency 10
• gemini-2.5-flash-preview-tts: concurrency 25

Queue Pattern

const queue: Promise<void>[] = [];

for (; currentIndex < Math.min(CONCURRENCY, slides.length); currentIndex++) {
  queue.push(processSlide(currentIndex));
}

while (currentIndex < slides.length) {
  const finished = await Promise.race(queue);
  const i = queue.indexOf(finished);
  if (i !== -1) queue.splice(i, 1);
  queue.push(processSlide(currentIndex++));
}

await Promise.all(queue);

Error Handling Model

• Save successful slides immediately (no rollback).
• Accumulate per-slide errors.
• Throw one summary error at end if any failures occurred.

This gives maximum throughput without losing already-completed work.