I2S digital clipping experiment

Host arithmetic: python audio_metrics.py
Host tests: python -B test_audio.py
Actual target intended: originalRP2040Pico/stockMicroPython1.26.0 only.
Copy capture_i2s.py and audio_metrics.py to Pico, verify exactSPH0645carrier/net/logic/alignment first, then run capture_i2s.py once.
Copy capture.pcm and capture-metadata.json to host; analyze with python audio_metrics.py capture.pcm
No author target/HW run. Callback does not prove continuous sampling; RP2 exposes no overflow counter.
External100kDATApull-down and100nFbypass. Never connect5V. No loud acoustic stimulation.

Peer functional repair: use stock RPI_PICO MicroPython 1.26.0, original RP2040, 125MHz, exclusive fresh GP10/11/12 and I2S0/PIO/DMA resources. GP10 OUTOVER inversion is mandatory for this exact microphone/backend. Power-cycle after any initialization/cleanup failure.
Run host tests with: python -B -m unittest -v test_audio test_phase
The included primary/machine_i2s-v126.c supports the opcode model; no firmware build or physical clock/data qualification occurred. Verify loaded DATA HIGH>=2.0V/LOW<=0.8V and correct falling-edge sampling before interpreting actual data.
