When NN exceeds 0xFC, the codec extends to 12-bit NN by using the
low nibble of the TYPE byte as the high nibble of NN:
1X NN → nibble-delta block, NN = (X << 8) | NN_byte
2X NN → int8-delta block, same NN encoding
Walker and decode_waveform_v2 now handle both narrow (X=0) and wide
(X != 0) forms uniformly.
Discovered while investigating why SP0/SS0/SV0/event-b walkers stopped
mid-event. SP0 segment 12 (V continuation, cycle 3) starts with
"11 90" — high nibble of byte 0 = 1 (= nibble-delta block type), low
nibble = 1 plus byte 1 = 0x90 → NN = 0x190 = 400 nibble deltas in
202 bytes. Walker was rejecting "11" as a non-tag.
Sample count went from 47,364 to 72,972 verified byte-exact:
event-a: 9984 (full) was 9984 (full)
event-b: 6912 (full) was 738
event-c: 3840 (full) was 3840 (full)
event-d: 3840 (full) was 3840 (full)
JQ0: 9984 (full) was 9984 (full)
V70: 9984 (full) was 9984 (full)
SP0: 9984 (full) was 5122
SS0: 9222 (-7 tail) was 1758
SV0: 9222 (-7 tail) was 2114
7 of 9 fixtures now decode end-to-end across all 3 geo channels.
The 2 remaining (SS0, SV0) are missing only 1-7 tail samples per
channel — minor walker edge case at the very end.
74 tests pass (was 71).
Claude
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