codec: wire decode_waveform_v2 into production; add MicL dB helper

Replaces the broken legacy int16 LE decoder in client.py with the
verified multi-channel codec.  Three changes:

1. blastware_file.extract_body_bytes(a5_frames) — new helper that
   factors out the body-reconstruction logic from write_blastware_file
   so both writers (BW binary) and decoders (sample arrays) can use
   the same canonical bytes.

2. waveform_codec.decode_a5_frames(a5_frames) — production entry point.
   Returns the raw_samples dict consumers expect (Tran/Vert/Long as
   int16 ADC counts; MicL as native ADC counts).  Internally:
     A5 frames → extract_body_bytes → decode_waveform_v2
                → decoded_to_adc_counts (geos ×16; mic pass-through)

3. waveform_codec.mic_count_to_db(count) — MicL ADC → dB(L) per BW's
   display formula:
     dB = sign(count) × (81.94 + 20 × log10(|count|))   for |count| ≥ 1
   Verified against V70 fixture: count=813 → 140.14 dB (BW PSPL 140.1).

client.py:_decode_a5_waveform is reduced to a thin wrapper that calls
decode_a5_frames and populates event.raw_samples.  Original implementation
preserved as _decode_a5_waveform_LEGACY (dead code; reference only).

Also fixed a tail-end bug in decode_waveform_v2 where trailer-section
"40 02" markers (containing ASCII serial bytes, NOT real segment headers)
were being mis-interpreted, producing 2 spurious samples per channel at
the end of each event.  Added bytes [12:14] == "02 00" validation to
reject non-header markers.

7 new pytest tests cover the new helpers and dB conversion.  Total:
71 passing (up from 64).

Known limitation (carried over from before): the walker still stops
mid-event on the loudest fixtures (SP0/SS0/SV0/event-b) at some
mid-segment edge cases not yet characterized.  Every sample reached
is decoded correctly; the walker just doesn't reach all of them.
Loud events still yield 5,000–15,000 byte-exact samples each.

minimateplus/client.py

@@ -1500,22 +1500,69 @@ def _decode_a5_waveform(
     (BULK_WAVEFORM_STREAM) frame payloads and populate event.raw_samples,
     event.total_samples, event.pretrig_samples, and event.rectime_seconds.
 
-    This requires ALL A5 frames (stop_after_metadata=False), not just the
-    metadata-bearing subset.
+    Wired up 2026-05-11 to the verified ``decode_waveform_v2`` codec (see
+    ``minimateplus/waveform_codec.py`` and ``docs/waveform_codec_re_status.md``).
+    Replaces the legacy int16 LE decoder, which produced full-scale ±32K
+    noise on every event because the body bytes are encoded, not raw
+    samples.
 
-    ── Waveform format (confirmed from 4-2-26 blast capture) ───────────────────
-    The blast waveform is 4-channel interleaved signed 16-bit little-endian,
-    8 bytes per sample-set:
+    Output convention (preserved from the legacy decoder):
+      ``event.raw_samples`` is a dict with keys "Tran", "Vert", "Long",
+      "MicL" mapping to lists of **int16 ADC counts**.  Multiply by
+      ``geo_range / 32768`` for geo channels to get in/s; use
+      :func:`minimateplus.waveform_codec.mic_count_to_db` for mic dB(L).
+
+    ``total_samples`` / ``pretrig_samples`` / ``rectime_seconds`` are set
+    to ``None`` so the caller backfills from compliance_config (the
+    authoritative source — STRT fields aren't reliable).
+    """
+    from .waveform_codec import decode_a5_frames
+
+    event.total_samples = None
+    event.pretrig_samples = None
+    event.rectime_seconds = None
+
+    if not frames_data:
+        log.debug("_decode_a5_waveform: no frames provided")
+        return
+
+    decoded = decode_a5_frames(frames_data)
+    if decoded is None:
+        log.warning("_decode_a5_waveform: codec returned no samples")
+        return
+
+    event.raw_samples = decoded
+    log.debug(
+        "_decode_a5_waveform: decoded %d/%d/%d/%d samples (T/V/L/M)",
+        len(decoded.get("Tran", [])),
+        len(decoded.get("Vert", [])),
+        len(decoded.get("Long", [])),
+        len(decoded.get("MicL", [])),
+    )
+
+
+def _decode_a5_waveform_LEGACY(
+    frames_data: list[S3Frame],
+    event: Event,
+) -> None:
+    """
+    LEGACY decoder — kept for reference only.  DO NOT CALL.
+
+    This is the int16 LE decoder that produced full-scale ±32K noise
+    on every event.  Retracted 2026-05-08; replaced 2026-05-11 with
+    the verified codec in :mod:`minimateplus.waveform_codec`.  See
+    ``docs/instantel_protocol_reference.md §7.6.1`` for the full history.
+
+    ── Waveform format (LEGACY — WRONG) ────────────────────────────────
+    Claimed 4-channel interleaved signed 16-bit little-endian, 8 bytes
+    per sample-set:
 
         [T_lo T_hi V_lo V_hi L_lo L_hi M_lo M_hi] × N
 
-    where T=Tran, V=Vert, L=Long, M=Mic.  Channel ordering follows the
-    Blastware convention [Tran, Vert, Long, Mic] = [ch0, ch1, ch2, ch3].
+    where T=Tran, V=Vert, L=Long, M=Mic.
 
-    ⚠️  Channel ordering is a confirmed CONVENTION — the physical ordering on
-        the ADC mux is not independently verifiable from the saturating blast
-        captures we have.  The convention is consistent with Blastware labeling
-        (Tran is always the first channel field in the A5 STRT+waveform stream).
+    The body bytes are actually a tagged delta+RLE stream — this
+    interpretation was wrong.
 
     ── Frame structure ──────────────────────────────────────────────────────────
     A5[0] (probe response):