New "auto" option (now the default) on the Sampler's input_sr. detect_input_sr
finds the spectral cutoff cliff (steepest drop) and its dB confidence: effective
cutoff = that cliff if confident, else sr/2 — one rule that covers band-limited
(→ matched input_sr), full-band (→ 24000), and genuine low-rate files
(→ their rate). Rounds DOWN to the nearest supported Nyquist to avoid feeding
the model an empty band. Logs its decision. Falls back to 24000 when unsure.
Tests cover sharp 4/6/8/12 kHz cutoffs, full-band, genuine-8kHz, silence, stereo.
Verified end-to-end on the real model (8 kHz clip -> auto picks 16000).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
