PixelMapper and AdvancedPixelMapper in calibration.py used to carry
byte-for-byte copies of two ~80-line numpy kernels (audit finding M4):
* the vectorised average-colour-per-LED path with its cumsum + take
scratch-buffer dance; and
* the per-LED fallback loop for median / dominant colour modes.
Lift both into a new ``core.capture.edge_interpolation`` module exposing
``average_edge_to_leds(edge_pixels, edge_name, led_count, cache,
cache_key)`` and ``fallback_edge_to_leds(edge_pixels, edge_name,
led_count, calc_color)``. The cache parameter is the caller-owned dict
(``self._edge_cache``) so allocations still happen once per
(edge_len, led_count) signature — the difference is that the
boundary-builder, the buffer set, and the inner numpy ops live in
exactly one place.
PixelMapper keys its cache by edge name (``"top"`` / ``"left"`` etc.);
AdvancedPixelMapper keys by line-index int (same dict, no collision).
Both mappers' ``_map_edge_average`` / ``_map_edge_fallback`` shrink to
single delegating lines.
Tests: 9 new kernel-level tests cover uint8 dtype + shape, the cache
reuse / rebuild contract, independent cache keying, a gradient input
producing a monotonic output, the calc_color callable contract for the
fallback path, and segment-position tracking for both axes. 30
existing calibration tests stay green; ruff clean.
alexei.dolgolyov
5fec8db901