fix(idf_waveforms): _find_waveform_body_offset() — scans every 00 02 00 magic past offset 0x0E00, runs decode_waveform_v2 on each candidate, picks the one that returns the most samples. Validated on 483 prod IDFW files: 0 preamble-only events (was ~50%), 355/483 fully decode, 126/483 partial (BW codec walker-stops-early on loud events — known issue).

IDFH now synthesises a 1-sample-per-interval array from the binary intervals and writes an .h5 so the existing renderer works unchanged. Each "sample" is the per-interval peak ADC count → h5_value = count × geo_fs/32768 yields the right bar height.

micromate/idf_file.py

@@ -62,12 +62,23 @@ _THOR_PREFIX = b"\x00\x12\x01\x00\x00\x00"
 _BW_STRAY_PREFIX = b"\x10\x00\x01\x80\x00\x00"
 _INSTANTEL_TAG = b"Instantel"
 
-# Constant body offset for sig-A IDFW files (verified across 151/154 corpus
-# files in tests/fixtures/THORDATA_example).  The body is the segment-rotated
-# block stream consumed by decode_waveform_v2; bytes [0:3] are the magic
-# ``00 02 00`` preamble.
+# Most common body offset for sig-A IDFW files (~50% of prod events;
+# 151/154 in the original tests/fixtures/THORDATA_example corpus).  The
+# body is the segment-rotated block stream consumed by decode_waveform_v2;
+# bytes [0:3] are the magic ``00 02 00`` preamble.  Production events
+# routinely use other offsets — see :func:`_find_waveform_body_offset`
+# for the dynamic scan.  This constant survives only as the priority hint.
 _BODY_START_SIG_A = 0x0F1F
 
+# Magic bytes that mark a candidate waveform-body preamble.
+_BODY_MAGIC = b"\x00\x02\x00"
+
+# Where to start looking for body candidates inside the file.  Skip the
+# fixed-header region where the same magic legitimately appears inside
+# channel-test records and the compliance block (offsets 0x015d, 0x091c,
+# 0x0ae2, 0x0d30 in observed events).
+_BODY_SCAN_FLOOR = 0x0E00
+
 # Geophone count → in/s, derived from sidecar ground truth: the smallest
 # non-zero sample in 1,014-file corpus is 0.0003 in/s.
 _GEO_LSB_IPS = 0.0003
@@ -179,17 +190,65 @@ def extract_binary_metadata(buf: bytes) -> IdfBinaryMetadata:
 # ─── Sample decoder + unit conversion ───────────────────────────────────────
 
 
+def _find_waveform_body_offset(buf: bytes) -> Optional[int]:
+    """Pick the file offset of the waveform body by trial-decoding every
+    ``00 02 00`` magic position past the fixed-header region.
+
+    The body's location isn't fixed across all sig-A IDFW files — about
+    half the production events use ``0x0f1f``, but the rest have offsets
+    that shift based on header padding / channel-config layout.  We
+    auto-detect by:
+
+      1. Find every ``00 02 00`` occurrence past ``_BODY_SCAN_FLOOR``.
+      2. Try ``decode_waveform_v2()`` on each candidate.
+      3. Pick the offset whose decoded sample count is largest.
+
+    Returns the offset, or ``None`` if no candidate yielded more than
+    the trivial 2-sample preamble (= "no real body found").
+
+    Costs ~2-8 trial decodes per file; in practice the first candidate
+    past 0x0e00 is usually the right one.
+    """
+    if len(buf) < _BODY_SCAN_FLOOR + 8:
+        return None
+    best: Optional[tuple[int, int]] = None   # (total_samples, offset)
+    i = _BODY_SCAN_FLOOR
+    while True:
+        j = buf.find(_BODY_MAGIC, i)
+        if j < 0:
+            break
+        i = j + 1
+        try:
+            decoded = decode_waveform_v2(buf[j:])
+        except Exception:
+            continue
+        if not decoded:
+            continue
+        total = sum(len(v) for v in decoded.values())
+        # A "real" body has more than just the 2-sample preamble.
+        if total <= 2:
+            continue
+        if best is None or total > best[0]:
+            best = (total, j)
+    return best[1] if best else None
+
+
 def _decode_waveform_samples(buf: bytes) -> Optional[dict]:
-    """Decode samples from the sig-A body starting at file offset 0x0f1f.
+    """Decode samples from the sig-A waveform body.
 
     Returns the raw decoder counts dict — geo LSB = 0.0003 in/s, mic in
     its own count unit (see :func:`mic_count_to_psi`).  Returns None if
-    decoding fails.
+    no usable body is found.
+
+    Uses :func:`_find_waveform_body_offset` to locate the body — the
+    file-offset varies across events (~50% sit at the canonical
+    ``0x0f1f`` but the rest don't), so the previous hardcoded constant
+    silently produced 2-sample preamble-only output for half the corpus.
     """
-    if len(buf) < _BODY_START_SIG_A + 8:
+    off = _find_waveform_body_offset(buf)
+    if off is None:
         return None
-    body = buf[_BODY_START_SIG_A:]
-    return decode_waveform_v2(body)
+    return decode_waveform_v2(buf[off:])
 
 
 def geo_count_to_ips(count: int) -> float: