codec-re: channel rotation CONFIRMED — full multi-channel decoder works

The segment-channel scoring analyzer (from scratch/next_experiment_skeleton.py)
ran and immediately confirmed the rotation hypothesis:

  SP0 seg 0: best fit Vert  508/508  ✓
  SP0 seg 1: best fit Long  508/508  ✓
  SP0 seg 3: best fit Tran  508/508  ✓  (Tran continuation)
  SP0 seg 5: best fit Long  508/508  ✓
  SP0 seg 9: best fit Long  508/508  ✓
  V70 seg 0: best fit Vert  508/508  ✓
  V70 seg 1: best fit Long  508/508  ✓

Channels rotate Tran → Vert → Long → MicL per 40 02 segment header.

Also discovered the segment header has DOUBLE duty: bytes [14:18] anchor
the NEW segment's channel (2 samples as int16 BE in 16-count units), AND
bytes [0:4] extend the PREVIOUS channel by 2 more samples (2 deltas as
int16 BE).  This is the same "2 anchors + delta stream" structure as the
body preamble for Tran.

decode_waveform_v2 now returns full per-channel sample dicts.
Byte-exact verified ranges:
  V70: Tran 512, Vert 512, Long 512   (all first segments)
  JQ0: Tran 512, Vert 258
  SP0: Long 1536 (all 3 L segments)

Still open: the 30 NN block format (high-amplitude packed deltas) —
appears mid-segment when single-byte deltas can't carry the magnitude.

6 new tests bring the count to 46.  All passing.

analysis/verify_full_decode.py

@@ -0,0 +1,32 @@
+"""Verify decode_waveform_v2 against BW ASCII truth for all fixtures."""
+import sys
+sys.path.insert(0, ".")
+from analysis.load_bundle import _parse_txt
+from minimateplus.waveform_codec import decode_waveform_v2
+
+
+def main():
+    for stem in ("M529LL1A.SP0", "M529LL1A.SS0", "M529LL1A.SV0",
+                 "M529LL1L.JQ0", "M529LL1L.V70"):
+        path = f"tests/fixtures/5-11-26/{stem}"
+        with open(path, "rb") as f:
+            body = f.read()[43:-26]
+        _, samples = _parse_txt(path + ".TXT")
+        decoded = decode_waveform_v2(body)
+        if decoded is None:
+            print(f"{stem}: decoder returned None")
+            continue
+
+        print(f"\n=== {stem} ===")
+        for ch in ("Tran", "Vert", "Long"):
+            truth = [round(v * 200) for v in samples[ch]]
+            pred = decoded[ch]
+            n = min(len(pred), len(truth))
+            matches = sum(1 for i in range(n) if pred[i] == truth[i])
+            div = next((i for i in range(n) if pred[i] != truth[i]), -1)
+            print(f"  {ch}: decoded={len(pred):>5}  truth={len(truth):>5}  "
+                  f"matches={matches:>5}/{n:<5}  first div={div}")
+
+
+if __name__ == "__main__":
+    main()