fix(codec): geo full scale is 32000 counts; 4 walker framing cases; channel-id from header

Two independent bugs, both found by diffing 75 production events against
their preserved Blastware ASCII exports (<store>/<serial>/<file>_ASCII.TXT).

1. Geo full scale was wrong — every geophone reading was 2.34% low.
   The codec emits geo samples in 16-count units with a documented LSB of
   exactly 0.005 in/s, and decoded_to_adc_counts multiplies by 16, so one
   ADC count is 0.005/16 in/s and 10.000 in/s is 10.0/(0.005/16) = 32000
   counts.  sfm/event_hdf5.py and minimateplus/event_file_io.py both
   divided by 32768 (2^15), scaling every sample and derived peak down by
   1 - 32000/32768.  The error scales with amplitude, so it was invisible
   on quiet events and worst on the loud ones that matter for compliance.
   Mic is unaffected (it back-solves its scale from the device peak).

   216 per-channel comparisons: 32768 -> 151/216 exact, worst error 0.238
   in/s on a 10 in/s event; 32000 -> 216/216 exact, worst 0.005 = 1 LSB.

2. walk_body silently truncated channels on four unhandled framing cases.
   An unrecognised tag ends the walk and decode_waveform_v2 returns
   whatever it got, so this surfaced as short channels, never an error:
     - wide-NN RLE `0X NN` (runs longer than 252 samples)
     - `30 NN` with NN > 0x10 (the old cap was arbitrary)
     - variable-width `40 NN` headers: NN counts previous-channel
       continuation deltas, so the header is 2*NN + 16 bytes; `40 01`
       and `40 03` occur alongside `40 02`
     - tagless segment headers: no `40 NN` tag at all, just the 14-byte
       tail [field2:2][len:2][channel_id:4][marker:2][anchors:4]

Also: the header field documented as a "monotonic uint32 LE counter" is
really [channel_id][00][00][segment_index], with 0x46=Tran 0x47=Vert
0x48=Long 0x49=MicL — verified on 1697/1697 segment headers, zero
disagreements.  decode_waveform_v2 now takes the channel from that field
instead of rotation position, which was fragile: one missed header
desynced every channel after it.

parse_segment_header now returns n_prev_deltas/prev_deltas/marker/
anchors/channel/segment_index; the old fixed_pattern (02 00 00 01)
conflated the 2-byte marker with the first anchor.

Ground-truth corpus, end to end through the production path:
  exact 37 -> 72, truncated 23 -> 3, full-length value errors 15 -> 0.
Store-wide, 729 of 1388 series-3 waveform events decode differently and
728 gain samples; the scale fix changes float values on all of them, so
stored .h5 files need regenerating.

Still open: 3 events truncate at a header variant with a variable-width
prefix (2/4/6 bytes) before the channel id and an `01 00` marker.
Documented in docs/instantel_protocol_reference.md with byte offsets.

+20 tests.  No regressions: the byte-exact fixture suite still passes and
the full-suite failure list is unchanged from baseline (16 pre-existing
failures from gitignored fixtures).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HgTe8CamXAHcAmaQ6QNcog

sfm/event_hdf5.py

@@ -77,6 +77,20 @@ _GEO_FS_BY_RANGE = {
 }
 _INT16_FS = 32768.0
 
+# Geophone full-scale count.  NOT 32768: the verified body codec emits geo
+# samples in 16-count units whose documented LSB is exactly 0.005 in/s, and
+# ``waveform_codec.decoded_to_adc_counts`` multiplies by 16 — so one ADC count
+# is 0.005/16 in/s and Normal range (10.000 in/s) is 10.0 / (0.005/16) = 32000
+# counts.  Using 32768 here made every geophone reading 2.3% low
+# (1 - 32000/32768 = 0.0234).
+#
+# Confirmed 2026-08-25 against 216 per-channel comparisons with the preserved
+# Blastware ASCII exports: 32000 gives 216/216 exact within 1 LSB (worst error
+# 0.005 in/s); 32768 gave 151/216 with a worst error of 0.238 in/s on a
+# 10 in/s event.  The mic path is unaffected — it back-solves its own scale
+# from the device-reported peak (see _mic_scale_factor).
+_GEO_INT16_FS = 32000.0
+
 # Default mic conversion: ADC count → psi.  Approximate; exact factor
 # depends on firmware reference voltage and mic sensitivity, neither of
 # which is independently confirmed.  We try to refine it from the device-
@@ -125,15 +139,14 @@ def _samples_to_float(
 ) -> np.ndarray:
     """Convert int16 ADC counts → float32 physical units.
 
-    Uses _INT16_FS=32768 (not 32767) so that a count of -32768 maps to
-    exactly -full_scale and +32767 maps to ~+full_scale * 32767/32768.
-    Matches the device firmware's documented mapping (see CLAUDE.md
-    geo_hardware_constant rationale).
+    Uses _GEO_INT16_FS=32000 (see the constant's rationale): one decoder
+    unit (16 ADC counts) is exactly 0.005 in/s, so full scale is 32000
+    counts, not 32768.
     """
     if not samples_int16:
         return np.array([], dtype=np.float32)
     arr = np.asarray(samples_int16, dtype=np.int32)  # int32 to avoid overflow during scale
-    return (arr.astype(np.float32) * (full_scale / _INT16_FS)).astype(np.float32)
+    return (arr.astype(np.float32) * (full_scale / _GEO_INT16_FS)).astype(np.float32)
 
 
 def _mic_scale_factor(