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Per plan Task 2. Adds <audio id=aud-b>; blendAudio(lo,frac) mixes the two adjacent scale soundtracks by knob fraction (element reuse across crossings so only the genuinely-new scale reloads); restAudio settles a single scale at rest. Diagnostic readout now reports whichever element is audible. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>