fix: two ring-buffer bugs in DelayNode::delayBufferOperation

[OhByron]

Summary

Two bugs in DelayNode::delayBufferOperation that together cause periodic clicking artifacts and inaudible delay echo on Android.

Bug 1 — Inverted wraparound index (framesToEnd)

framesToEnd was computed as the overflow count (frames past the buffer end) but used as the size of the pre-wrap chunk (frames remaining before the buffer end):

// Before (buggy): overflow count, not pre-wrap count
int framesToEnd = operationStartingIndex + framesToProcess - delayBuffer_->getSize();

// After: correct pre-wrap count
int framesToEnd = static_cast<int>(delayBuffer_->getSize()) - static_cast<int>(operationStartingIndex);

This caused audio to be written/read at wrong positions on every buffer boundary crossing.

Bug 2 — Pre-wrap chunk not zeroed after READ

The READ path only zeroed the second (post-wrap) chunk. The first chunk — frames from operationStartingIndex to the buffer end — was consumed but never cleared. On the next full buffer rotation (~1 s for a 1 s max-delay buffer) that stale data was re-read as new audio:

} else { // READ
  processingBuffer->sum(
      *delayBuffer_, operationStartingIndex, processingBufferStartIndex, framesToEnd);
  delayBuffer_->zero(operationStartingIndex, framesToEnd);  // added
}

Symptoms (Android, Nokia XR20, sampleRate 48000)

• Periodic metronome-like clicking whose rate scales with delayTime.value — fixed by Bug 1
• ~1 s periodic tick independent of delay time — fixed by Bug 2
• Delay echo inaudible — resolved once both fixes are applied

Test plan

• Create AudioContext, wire OscillatorNode → DelayNode → GainNode(wet) → destination with a separate dry path
• Set delayTime to a value < maxDelayTime (e.g. 0.3 s, 0.95 s)
• Start oscillator, play for several seconds — confirm no periodic clicking
• Stop oscillator — confirm echo tail is audible for ~delayTime seconds after stop
• Verify no regression on iOS

Tested on Android (Nokia XR20, Android 14) via a local dev build with both fixes applied.

🤖 Generated with Claude Code

[mdydek]

one nitpick and I think we're ready to go

[mdydek]

Suggested change

	int framesToEnd =
	static_cast<int>(operationStartingIndex + framesToProcess - delayBuffer_->getSize());
	static_cast<int>(delayBuffer_->getSize()) - static_cast<int>(operationStartingIndex);
	auto framesToEnd =
	static_cast<int>(delayBuffer_->getSize() - operationStartingIndex);