fix: update STRT record parsing to reflect confirmed offsets and derive total/pretrig_samples from compliance config

The server now re-computes rectime_seconds using the actual sample rate from the compliance config (overriding the default 1024 in the client), so if the device runs at 2048 or 4096 sps it's still correct.

Viewer — The rectime display now shows Xs (stored) / Ys (cfg) so you can compare the STRT-derived duration against the compliance config's record_time setting side-by-side. I also clamped the y-axis to ±(0C peak × 1.4) so near-saturation decode artifacts don't squash the real blast signal into a flat line.

CLAUDE.md

@@ -163,6 +163,83 @@ record — 5A remains the sole source for those fields and they are set uncondit
 `stop_after_metadata=True` (default) stops the 5A loop as soon as `b"Project:"` appears,
 then sends the termination frame.
 
+### SUB 5A — STRT record layout and rectime_seconds (CORRECTED 2026-04-14)
+
+The STRT record is 21 bytes embedded at the start of A5[0] data.  Offsets relative to
+the `b'STRT'` magic bytes:
+
+```
++0..3   b'STRT'   magic
++4..5   flags     0xFF 0xFE (single-shot) or 0xFF 0xFD (continuous)
++6..9   next_key4  ← key of the NEXT stored event (NOT the current event) ← confirmed 2026-04-14
++10..13 prev_key4  ← key of the PREVIOUS stored event                     ← confirmed 2026-04-14
++14..15 UNKNOWN   (values seen: 0xDA63=55907, 0xF38F=62351, 0x5685=22149) — NOT total_samples
++16..17 UNKNOWN   (values seen: 0x0122=290, 0x011A=282, 0x00FA=250)       — NOT pretrig_samples
++18     uint8     record-MODE byte — NOT rectime in seconds
++19..20 0x00 0x00
+```
+
+**CONFIRMED field values (2026-04-14) from 3 desk-thump events, firmware S338.17:**
+
+| Field | What it is | Confirmed |
+|---|---|---|
+| +4..5 | 0xFFFE single-shot / 0xFFFD continuous | ✅ |
+| +6..9 | next_event_key (NOT current) | ✅ 3 events |
+| +10..13 | prev_event_key | ✅ 3 events |
+| +18 | mode byte: 0x46 ('F') = single-shot, 0x0E = continuous | ✅ |
+
+**CONFIRMED (2026-04-14) — total_samples and pretrig_samples are NOT stored in the STRT record.**
+The prior documented offsets (+14..15 for total_samples, +16..17 for pretrig_samples) were
+WRONG — confirmed by cross-checking STRT-derived rectime against compliance record_time
+(4-14-26): all 4 events give STRT-derived rectime of 21–61 s vs actual 3.0 s (ratio 7–20×).
+Extending the STRT dump to 32 bytes confirmed that bytes 21+ are the start of the raw ADC
+waveform samples, not more STRT fields.  Blastware itself derives total_samples and
+pretrig_samples from the compliance config — exactly what our fallback does.
+
+**The compliance-config fallback IS the correct permanent solution, not a workaround.**
+`_decode_a5_waveform` uses:
+  - `pretrig_samples = round(0.25 × sample_rate)` (compliance monitoring standard)
+  - `total_samples   = pretrig_samples + round(record_time × sample_rate)`
+
+**CONFIRMED (2026-04-14) — waveform starts at strt_pos + 21 (no preamble).**
+The original `sp + 27` skip (STRT 21B + null-pad 2B + 0xFF-sentinel 4B) was WRONG.
+The 6-byte "preamble" in the 4-2-26 blast capture (`00 00 ff ff ff ff`) was actually the
+first ~0.75 sample-sets of quiet pre-trigger ADC data misread as padding.  Desk-thump
+events show different bytes at positions 21-26 (e.g. `00 10 02 00 ff fc`) — they are real
+ADC readings, not a fixed preamble.  The `sp + 27` skip discarded 6 bytes of real waveform
+data and misaligned the channel decode for all subsequent frames.  Fixed: `wave = w[sp+21:]`.
+
+The +6..9 next_key and +10..13 prev_key fields are confirmed across 4 events including the
+first-event-after-erase case (prev_key = self-reference `01110000`; next_key = device
+pre-allocates the predicted next slot even before any second event exists).
+
+**CRITICAL — strt[18] is a record-mode byte, NOT rectime_seconds (confirmed 2026-04-14):**
+Analysis of 15 distinct STRT records across the 4-9-26 ACH capture shows:
+- `flags=0xFFFE` (single-shot) → `strt[18] = 0x46` ('F') for EVERY event regardless of duration
+- `flags=0xFFFD` (continuous)  → `strt[18] = 0x0E` for EVERY event regardless of duration
+
+Do NOT use `strt[18]` for rectime.
+
+**Pre-trigger time is separate from record_time (confirmed 2026-04-14):**
+Blastware documentation states: "The default Time Scale is -0.25 second to 1 second — this
+negative number accounts for the pre-trigger set for compliance monitoring."  Therefore:
+- `record_time` (3.0 s) is POST-TRIGGER duration only
+- Pre-trigger = 0.25 s = 256 samples at 1024 sps (compliance monitoring standard default)
+- The pre-trigger field has NOT yet been located in the raw compliance config bytes
+- `_decode_a5_waveform` falls back to pretrig = 0.25 × sr from compliance standard
+- TODO: locate pretrig_time offset in ComplianceConfig — search around anchor or channel blocks
+
+The device bulk-streams zero-padded frames BEYOND the configured record window.  The
+viewer clips `displayCount = total_samples = pretrig + post_trig` to exclude this padding.
+
+**Validity checks in `_decode_a5_waveform`:**
+Check 1: `pretrig_samples >= total_samples` → invalid (original check).
+Check 2: STRT-derived rectime differs from `compliance_config.record_time` by more than 2×
+→ invalid.  Both failures fall back to the compliance-config derived values.
+`_decode_a5_waveform` logs `raw strt[0:21]` at WARNING level on any failure.
+Observed once (2026-04-14) with `strt[16:18] = 0x41 0x01` → pretrig=16641 (impossible).
+Root cause not yet identified — capture the warning log hex dump to diagnose.
+
 ### SUB 5A — end-of-stream signal (confirmed 2026-04-06)
 
 After streaming all waveform chunks, the device sends exactly **1 raw byte** in response to

bridges/ach_server.py

@@ -371,6 +371,7 @@ class AchSession:
                     full_waveform=True,
                     stop_after_index=stop_idx,
                     skip_waveform_for_keys=seen_keys if seen_keys else None,
+                    compliance_config=device_info.compliance_config if device_info else None,
                 )
 
                 # Filter to events whose keys we haven't saved before.
@@ -445,8 +446,19 @@ class AchSession:
                 # ── Persist to SQLite DB ─────────────────────────────────────
                 _session_start = datetime.datetime.now()
                 try:
+                    # Build waveform blobs for events that have full raw_samples
+                    _waveform_blobs = {}
+                    for _ev in new_events:
+                        if _ev._waveform_key and _ev.raw_samples:
+                            _blob = _build_waveform_blob(_ev)
+                            if _blob:
+                                _waveform_blobs[_ev._waveform_key.hex()] = _blob
+                    if _waveform_blobs:
+                        log.info("  [DB] waveform blobs prepared: %d", len(_waveform_blobs))
+
                     _ev_ins, _ev_skip = self.db.insert_events(
-                        new_events, serial=serial or self.peer, session_id=None
+                        new_events, serial=serial or self.peer, session_id=None,
+                        waveform_blobs=_waveform_blobs,
                     )
                     _ml_ins, _ml_skip = self.db.insert_monitor_log(
                         new_monitor_entries, session_id=None
@@ -599,6 +611,52 @@ def _event_to_dict(e: Event) -> dict:
     }
 
 
+def _build_waveform_blob(e: Event) -> Optional[str]:
+    """
+    Serialise a downloaded event's full waveform data as a JSON string for
+    storage in the DB waveform_blob column.
+
+    Returns the same shape as GET /device/event/{index}/waveform so the
+    waveform viewer can consume either source without modification.
+    Returns None if the event has no raw_samples (e.g. metadata-only download).
+    """
+    raw = e.raw_samples or {}
+    if not raw:
+        return None
+
+    pv = e.peak_values
+    peak_values = None
+    if pv:
+        peak_values = {
+            "tran":             pv.tran,
+            "vert":             pv.vert,
+            "long":             pv.long,
+            "micl_psi":         pv.micl,
+            "peak_vector_sum":  pv.peak_vector_sum,
+        }
+
+    ts = e.timestamp
+    timestamp_str = (
+        f"{ts.year:04d}-{ts.month:02d}-{ts.day:02d}T"
+        f"{ts.hour:02d}:{ts.minute:02d}:{ts.second:02d}"
+        if ts else None
+    )
+
+    blob = {
+        "index":           e.index,
+        "record_type":     e.record_type,
+        "timestamp":       timestamp_str,
+        "total_samples":   e.total_samples,
+        "pretrig_samples": e.pretrig_samples,
+        "rectime_seconds": e.rectime_seconds,
+        "samples_decoded": len(raw.get("Tran", [])),
+        "sample_rate":     e.sample_rate,
+        "peak_values":     peak_values,
+        "channels":        raw,
+    }
+    return json.dumps(blob)
+
+
 def _monitor_log_entry_to_dict(e: MonitorLogEntry) -> dict:
     return {
         "key":               e.key,

minimateplus/client.py

@@ -448,7 +448,7 @@ class MiniMateClient:
         proto.confirm_erase_all()
         log.info("delete_all_events: erase confirmed — device memory cleared")
 
-    def get_events(self, full_waveform: bool = False, debug: bool = False, stop_after_index: Optional[int] = None, skip_waveform_for_keys: Optional[set] = None) -> list[Event]:
+    def get_events(self, full_waveform: bool = False, debug: bool = False, stop_after_index: Optional[int] = None, skip_waveform_for_keys: Optional[set] = None, compliance_config: Optional["ComplianceConfig"] = None) -> list[Event]:
         """
         Download all stored events from the device using the confirmed
         1E → 0A → 0C → 5A → 1F event-iterator protocol.
@@ -479,6 +479,7 @@ class MiniMateClient:
             ProtocolError: on unrecoverable communication failure.
         """
         proto = self._require_proto()
+        _compliance_config = compliance_config   # passed through to _decode_a5_waveform
 
         log.info("get_events: requesting first event (SUB 1E)")
         try:
@@ -603,12 +604,12 @@ class MiniMateClient:
                             "get_events: 5A full waveform download for key=%s", cur_key.hex()
                         )
                         a5_frames = proto.read_bulk_waveform_stream(
-                            cur_key, stop_after_metadata=False, max_chunks=128
+                            cur_key, stop_after_metadata=False, max_chunks=2048
                         )
                         if a5_frames:
                             a5_ok = True
                             _decode_a5_metadata_into(a5_frames, ev)
-                            _decode_a5_waveform(a5_frames, ev)
+                            _decode_a5_waveform(a5_frames, ev, compliance_config=_compliance_config)
                             log.info(
                                 "get_events: 5A decoded %d sample-sets",
                                 len((ev.raw_samples or {}).get("Tran", [])),
@@ -1311,6 +1312,7 @@ def _decode_a5_metadata_into(frames_data: list[bytes], event: Event) -> None:
 def _decode_a5_waveform(
     frames_data: list[bytes],
     event: Event,
+    compliance_config: Optional["ComplianceConfig"] = None,
 ) -> None:
     """
     Decode the raw 4-channel ADC waveform from a complete set of SUB 5A
@@ -1336,15 +1338,22 @@ def _decode_a5_waveform(
 
     ── Frame structure ──────────────────────────────────────────────────────────
     A5[0] (probe response):
-        db[7:]  = [11-byte header] [21-byte STRT record] [6-byte preamble] [waveform ...]
+        db[7:]  = [11-byte header] [21-byte STRT record] [waveform ...]
         STRT:     b'STRT' at offset 11, total 21 bytes
-                  +8  uint16 BE: total_samples (expected full-record sample-sets)
-                  +16 uint16 BE: pretrig_samples (pre-trigger sample count)
-                  +18 uint8:     rectime_seconds (record duration)
-        Preamble: 6 bytes after the STRT record (confirmed from 4-2-26 blast capture):
-                  bytes 21-22: 0x00 0x00  (null padding)
-                  bytes 23-26: 0xFF × 4   (sync sentinel / alignment marker)
-        Waveform starts at strt_pos + 27 within db[7:].
+                  +4..5  0xFF 0xFE (single-shot) or 0xFF 0xFD (continuous)
+                  +6..9  next_event_key4  (device pre-allocates next slot)
+                  +10..13 prev_event_key4
+                  +14..15 UNKNOWN (not total_samples)
+                  +16..17 UNKNOWN (not pretrig_samples)
+                  +18    mode byte: 0x46 single-shot, 0x0E continuous
+                  +19..20 0x00 0x00
+        Waveform starts immediately at strt_pos + 21 (no preamble).
+        NOTE: The original 4-2-26 blast capture appeared to show a 6-byte
+        "preamble" (00 00 ff ff ff ff) after the STRT record, but this was
+        actually the first ~0.75 sample-sets of quiet pre-trigger ADC data
+        misread as padding.  Confirmed 2026-04-14: bytes 21+ are raw waveform.
+        total_samples and pretrig_samples are NOT stored in the STRT record;
+        they are derived from the compliance config (the correct permanent source).
 
     A5[1..N] (chunk responses):
         db[7:]  = [8-byte per-frame header] [waveform bytes ...]
@@ -1378,27 +1387,48 @@ def _decode_a5_waveform(
 
     # STRT record layout (21 bytes, offsets relative to b'STRT'):
     #   +0..3   magic  b'STRT'
-    #   +8..9   uint16 BE  total_samples  (full-record expected sample-set count)
-    #   +16..17 uint16 BE  pretrig_samples
-    #   +18     uint8      rectime_seconds
+    #   +4..5   0xFF 0xFE (single-shot) or 0xFF 0xFD (continuous)
+    #   +6..9   next_event_key4  (NOT current key — device pre-allocates next)
+    #   +10..13 prev_event_key4
+    #   +14..15 UNKNOWN — confirmed NOT total_samples (confirmed 2026-04-14)
+    #   +16..17 UNKNOWN — confirmed NOT pretrig_samples (confirmed 2026-04-14)
+    #   +18     mode byte: 0x46='F' single-shot, 0x0E continuous — NOT rectime
+    #   +19..20 0x00 0x00
+    # Bytes 21+ are raw ADC waveform samples — no preamble.
+    # total_samples / pretrig_samples are NOT stored in STRT at all.
+    # The compliance config fallback is the correct permanent source.
     strt = w0[strt_pos : strt_pos + 21]
     if len(strt) < 21:
         log.warning("_decode_a5_waveform: STRT record truncated (%dB)", len(strt))
         return
 
-    total_samples   = struct.unpack_from(">H", strt, 8)[0]
-    pretrig_samples = struct.unpack_from(">H", strt, 16)[0]
-    rectime_seconds = strt[18]
-
-    event.total_samples   = total_samples
-    event.pretrig_samples = pretrig_samples
-    event.rectime_seconds = rectime_seconds
-
-    log.debug(
-        "_decode_a5_waveform: STRT total_samples=%d pretrig=%d rectime=%ds",
-        total_samples, pretrig_samples, rectime_seconds,
+    log.info(
+        "_decode_a5_waveform: STRT raw[0:21]: %s",
+        strt.hex(' '),
     )
 
+    # STRT bytes +14..17 are unknown fields — confirmed NOT total/pretrig_samples
+    # (2026-04-14).  total_samples and pretrig_samples are derived from the
+    # compliance config, which is the correct permanent source.
+    _strt_invalid = True
+    _sample_rate_default = 1024
+    total_samples   = 0
+    pretrig_samples = 0
+    rectime_seconds = 0
+
+    log.info(
+        "_decode_a5_waveform: STRT flags=0x%04X  next_key=%s  prev_key=%s  "
+        "mode=0x%02X  → using compliance-config for total/pretrig",
+        struct.unpack_from(">H", strt, 4)[0],
+        strt[6:10].hex(),
+        strt[10:14].hex(),
+        strt[18],
+    )
+
+    event.total_samples   = 0   # will be overwritten by compliance-config fallback below
+    event.pretrig_samples = 0
+    event.rectime_seconds = 0
+
     # ── Collect per-frame waveform bytes with global offset tracking ─────────
     # global_offset is the cumulative byte count across all frames, used to
     # compute the channel alignment at each frame boundary.
@@ -1408,13 +1438,21 @@ def _decode_a5_waveform(
     for fi, db in enumerate(frames_data):
         w = db[7:]
 
-        # A5[0]: waveform begins after the 21-byte STRT record and 6-byte preamble.
-        # Layout: STRT(21B) + null-pad(2B) + 0xFF sentinel(4B) = 27 bytes total.
+        # A5[0]: waveform begins immediately after the 21-byte STRT record.
+        # Confirmed 2026-04-14: there is NO preamble after STRT — bytes 21+
+        # are raw ADC sample data.  The earlier sp+27 skip was eating 6 bytes
+        # of real waveform, misaligning the channel decode for all subsequent
+        # frames.
         if fi == 0:
             sp = w.find(b"STRT")
             if sp < 0:
                 continue
-            wave = w[sp + 27 :]
+            wave = w[sp + 21 :]
+            log.info(
+                "_decode_a5_waveform: A5[0] waveform starts at sp+21; "
+                "first 24 wave bytes: %s",
+                wave[:24].hex(' '),
+            )
 
         # Frame 7 carries event-time metadata strings ("Project:", "Client:", …)
         # and no waveform ADC data.
@@ -1490,10 +1528,28 @@ def _decode_a5_waveform(
 
         running_offset += len(wave)
 
+    n_decoded_total = len(tran)
     log.debug(
         "_decode_a5_waveform: decoded %d alignment-corrected sample-sets "
         "(skipped %d due to frame boundary misalignment)",
-        len(tran), n_sets - len(tran),
+        n_decoded_total, n_sets - n_decoded_total,
+    )
+    # Log first 16 and last 8 samples for every channel — essential for
+    # validating decoder output and diagnosing flatline / misalignment issues.
+    _N = min(16, n_decoded_total)
+    _L = max(0, n_decoded_total - 8)
+    log.info(
+        "_decode_a5_waveform: first %d samples — "
+        "Tran=%s  Vert=%s  Long=%s  Mic=%s",
+        _N,
+        tran[:_N], vert[:_N], long_[:_N], mic[:_N],
+    )
+    if n_decoded_total > 16:
+        log.info(
+            "_decode_a5_waveform: last 8 samples (idx %d–%d) — "
+            "Tran=%s  Vert=%s  Long=%s  Mic=%s",
+            _L, n_decoded_total - 1,
+            tran[_L:], vert[_L:], long_[_L:], mic[_L:],
         )
 
     event.raw_samples = {
@@ -1503,6 +1559,64 @@ def _decode_a5_waveform(
         "Mic":  mic,
     }
 
+    # ── Derive pretrig/total from compliance config (always — STRT doesn't store them) ──
+    # total_samples and pretrig_samples are not stored in the STRT record (confirmed
+    # 2026-04-14).  They are derived from compliance config record_time × sample_rate.
+    # _strt_invalid is always True; this block always runs.
+    #
+    # Formula:
+    #   post_trig  = record_time (s) × sample_rate (sps)
+    #   pretrig    = decoded_samples − post_trig
+    #
+    # This gives the pre-trigger window length, which correctly places t=0 in the
+    # waveform. If compliance_config is not available, leave pretrig=0 (viewer shows
+    # full waveform starting at t=0 — better than a crash or garbage).
+    n_decoded = len(tran)
+    if _strt_invalid:
+        if compliance_config is not None:
+            cc_sr = compliance_config.sample_rate or 1024
+            cc_rt = compliance_config.record_time
+            # Pre-trigger time is a separate device setting from Record Time.
+            # Blastware documentation confirms the compliance monitoring standard
+            # is 0.25 seconds pre-trigger ("the default Time Scale is -0.25 to 1
+            # second — this negative number accounts for the pre-trigger set for
+            # compliance monitoring").
+            # The pre-trigger field has not yet been located in the raw compliance
+            # config bytes; 0.25 s is used as the best-known default until it is
+            # decoded.  TODO: locate pretrig_time in ComplianceConfig bytes.
+            _PRETRIG_SECONDS_DEFAULT = 0.25
+            derived_pretrig = int(round(_PRETRIG_SECONDS_DEFAULT * cc_sr))
+            if cc_rt and cc_rt > 0:
+                post_trig_samples = int(round(cc_rt * cc_sr))
+                # Clip total to pretrig + post_trig so the viewer doesn't show the
+                # zero-padded tail frames the device appends beyond the record window.
+                event.total_samples   = derived_pretrig + post_trig_samples
+                event.pretrig_samples = derived_pretrig
+                event.rectime_seconds = int(round(cc_rt))
+                log.info(
+                    "_decode_a5_waveform: pretrig=%d (%.2fs compliance default)  "
+                    "post_trig=%d  total=%d  record_time=%.1fs  "
+                    "sr=%d sps  decoded=%d samples",
+                    derived_pretrig, _PRETRIG_SECONDS_DEFAULT,
+                    post_trig_samples, event.total_samples,
+                    cc_rt, cc_sr, n_decoded,
+                )
+            else:
+                event.total_samples   = n_decoded
+                event.pretrig_samples = derived_pretrig
+                log.warning(
+                    "_decode_a5_waveform: STRT invalid, compliance config missing "
+                    "record_time — pretrig=%d (%.2fs default), total=decoded %d",
+                    derived_pretrig, _PRETRIG_SECONDS_DEFAULT, n_decoded,
+                )
+        else:
+            event.total_samples = n_decoded
+            log.warning(
+                "_decode_a5_waveform: STRT invalid, no compliance config available "
+                "— pretrig left as 0, total set to decoded count %d",
+                n_decoded,
+            )
+
 
 def _extract_record_type(data: bytes) -> Optional[str]:
     """

sfm/database.py

@@ -81,6 +81,7 @@ CREATE TABLE IF NOT EXISTS events (
     sample_rate             INTEGER,
     record_type             TEXT,                   -- "single_shot" | "continuous"
     false_trigger           INTEGER NOT NULL DEFAULT 0,  -- 0=no, 1=yes (manual flag)
+    waveform_blob           TEXT,                       -- JSON waveform response (channels + metadata)
     created_at              TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now')),
     UNIQUE(serial, timestamp)
 );
@@ -216,6 +217,17 @@ class SeismoDb:
             """)
             log.info("_migrate: monitor_log table rebuilt OK")
 
+        # Migration 3: add waveform_blob column to events (nullable TEXT).
+        # ALter TABLE ADD COLUMN is safe in SQLite for nullable columns — no rebuild needed.
+        col_names = {
+            row[1]
+            for row in conn.execute("PRAGMA table_info(events)").fetchall()
+        }
+        if "waveform_blob" not in col_names:
+            log.info("_migrate: adding waveform_blob column to events")
+            conn.execute("ALTER TABLE events ADD COLUMN waveform_blob TEXT")
+            log.info("_migrate: waveform_blob column added OK")
+
     @staticmethod
     def _iso(dt: Optional[datetime.datetime]) -> Optional[str]:
         return dt.isoformat() if dt is not None else None
@@ -282,12 +294,19 @@ class SeismoDb:
         *,
         serial: str,
         session_id: Optional[str] = None,
+        waveform_blobs: Optional[dict[str, str]] = None,
     ) -> tuple[int, int]:
         """
         Insert triggered events. Silently skips duplicates (serial+timestamp).
         Returns (inserted, skipped).
+
+        waveform_blobs: optional mapping of waveform_key (hex str) → JSON string
+        containing the full waveform response (channels + metadata).  When provided,
+        the blob is stored alongside the event row and is retrievable via
+        GET /db/events/{id}/waveform.
         """
         inserted = skipped = 0
+        blobs = waveform_blobs or {}
         with self._connect() as conn:
             for ev in events:
                 key = ev._waveform_key.hex() if ev._waveform_key else None
@@ -307,6 +326,7 @@ class SeismoDb:
 
                 pv   = ev.peak_values
                 pi   = ev.project_info
+                blob = blobs.get(key)
 
                 try:
                     conn.execute(
@@ -315,8 +335,8 @@ class SeismoDb:
                             (id, serial, waveform_key, session_id, timestamp,
                              tran_ppv, vert_ppv, long_ppv, peak_vector_sum, mic_ppv,
                              project, client, operator, sensor_location,
-                             sample_rate, record_type)
-                        VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+                             sample_rate, record_type, waveform_blob)
+                        VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
                         """,
                         (
                             self._new_id(), serial, key, session_id, ts,
@@ -331,6 +351,7 @@ class SeismoDb:
                             pi.sensor_location if pi else None,
                             ev.sample_rate,
                             ev.record_type,
+                            blob,
                         ),
                     )
                     inserted += 1
@@ -387,6 +408,23 @@ class SeismoDb:
             )
         return cur.rowcount > 0
 
+    def get_event_waveform(self, event_id: str) -> tuple[bool, Optional[str]]:
+        """
+        Return (found, waveform_blob) for a given event UUID.
+
+        found=False means the event row doesn't exist.
+        found=True, blob=None means the event exists but has no stored waveform
+        (e.g. downloaded before waveform storage was implemented).
+        found=True, blob=<str> means the full waveform JSON is available.
+        """
+        with self._connect() as conn:
+            row = conn.execute(
+                "SELECT waveform_blob FROM events WHERE id = ?", (event_id,)
+            ).fetchone()
+        if row is None:
+            return False, None
+        return True, row["waveform_blob"]
+
     # ── Monitor log ───────────────────────────────────────────────────────────
 
     def insert_monitor_log(

sfm/server.py

@@ -662,7 +662,11 @@ def device_event_waveform(
             with _build_client(port, baud, host, tcp_port, timeout=120.0) as client:
                 info = client.connect()
                 # stop_after_index avoids downloading events beyond the one requested.
-                events = client.get_events(full_waveform=True, stop_after_index=index)
+                events = client.get_events(
+                    full_waveform=True,
+                    stop_after_index=index,
+                    compliance_config=info.compliance_config if info else None,
+                )
                 matching = [ev for ev in events if ev.index == index]
                 return matching[0] if matching else None, info
         ev, info = _run_with_retry(_do, is_tcp=_is_tcp(host))
@@ -689,13 +693,22 @@ def device_event_waveform(
     if sample_rate is None and info.compliance_config:
         sample_rate = info.compliance_config.sample_rate
 
+    # Recompute rectime_seconds using the actual sample rate now that we have it.
+    # _decode_a5_waveform used 1024 sps as default; override if device says otherwise.
+    # strt[18] is a record-mode byte (0x46 / 0x0E), NOT rectime in seconds.
+    rectime_seconds = ev.rectime_seconds
+    if (ev.total_samples is not None and ev.pretrig_samples is not None
+            and sample_rate and sample_rate > 0):
+        post_trig = max(0, ev.total_samples - ev.pretrig_samples)
+        rectime_seconds = round(post_trig / sample_rate, 2)
+
     result = {
         "index":           ev.index,
         "record_type":     ev.record_type,
         "timestamp":       _serialise_timestamp(ev.timestamp),
         "total_samples":   ev.total_samples,
         "pretrig_samples": ev.pretrig_samples,
-        "rectime_seconds": ev.rectime_seconds,
+        "rectime_seconds": rectime_seconds,
         "samples_decoded": samples_decoded,
         "sample_rate":     sample_rate,
         "peak_values":     _serialise_peak_values(ev.peak_values),
@@ -1006,6 +1019,41 @@ def db_set_false_trigger(
     return {"status": "ok", "event_id": event_id, "false_trigger": value}
 
 
+@app.get("/db/events/{event_id}/waveform")
+def db_event_waveform(event_id: str) -> dict:
+    """
+    Return the stored waveform blob for a DB event.
+
+    The response shape is identical to GET /device/event/{index}/waveform so the
+    waveform viewer can consume either source without modification:
+      - total_samples, pretrig_samples, rectime_seconds, samples_decoded
+      - sample_rate
+      - peak_values  (tran, vert, long, micl_psi, peak_vector_sum)
+      - channels     ({"Tran": [...], "Vert": [...], "Long": [...], "Mic": [...]})
+
+    Returns 404 if the event doesn't exist, 422 if the event exists but has no
+    stored waveform (downloaded before waveform storage was implemented).
+    """
+    import json as _json
+    db   = _get_db()
+    found, blob_str = db.get_event_waveform(event_id)
+    if not found:
+        raise HTTPException(status_code=404, detail=f"Event {event_id} not found")
+    if blob_str is None:
+        raise HTTPException(
+            status_code=422,
+            detail=(
+                f"Event {event_id} has no stored waveform. "
+                "Waveform storage requires ACH server v0.11+. "
+                "Re-download the event from the device to backfill."
+            ),
+        )
+    try:
+        return _json.loads(blob_str)
+    except Exception as exc:
+        raise HTTPException(status_code=500, detail=f"Waveform blob corrupt: {exc}") from exc
+
+
 @app.get("/db/monitor_log")
 def db_monitor_log(
     serial:  Optional[str] = Query(None, description="Filter by unit serial"),

sfm/sfm_webapp.html

@@ -548,6 +548,18 @@
     .ft-toggle-btn:hover { border-color: var(--red); color: var(--red); }
     .ft-toggle-btn.flagged { border-color: var(--red); color: var(--red); background: rgba(248,81,73,0.1); }
 
+    .wf-btn {
+      background: none;
+      border: 1px solid var(--border);
+      border-radius: var(--radius);
+      color: var(--accent);
+      cursor: pointer;
+      font-size: 13px;
+      padding: 1px 6px;
+      line-height: 1;
+    }
+    .wf-btn:hover { background: rgba(56,139,253,0.15); border-color: var(--accent); }
+
     .db-empty {
       color: var(--text-mute);
       font-size: 13px;
@@ -921,6 +933,7 @@
       <table class="db-table" id="hist-table">
         <thead>
           <tr>
+            <th></th>
             <th>Timestamp</th>
             <th>Serial</th>
             <th>Tran (in/s)</th>
@@ -1744,7 +1757,9 @@ async function loadHistory() {
     const tr = document.createElement('tr');
     const pvs = ev.peak_vector_sum;
     const maxPPV = Math.max(ev.tran_ppv ?? 0, ev.vert_ppv ?? 0, ev.long_ppv ?? 0);
+    const waveformUrl = `${api()}/waveform?db_id=${encodeURIComponent(ev.id)}&api_base=${encodeURIComponent(api())}`;
     tr.innerHTML = `
+      <td><button class="wf-btn" onclick="window.open('${waveformUrl}','_blank')" title="View waveform">〜</button></td>
       <td>${_fmtTs(ev.timestamp)}</td>
       <td class="td-key">${ev.serial ?? '—'}</td>
       <td class="${_ppvClass(ev.tran_ppv)}">${_ppvFmt(ev.tran_ppv)}</td>

sfm/waveform_viewer.html

@@ -193,6 +193,10 @@
   </div>
   <button id="connect-btn" onclick="connectUnit()">Connect</button>
   <button id="load-btn" onclick="loadWaveform()" disabled>Load Waveform</button>
+  <label style="display:flex;align-items:center;gap:4px;color:#8b949e;font-size:12px;cursor:pointer">
+    <input type="checkbox" id="force-reload" style="accent-color:#1f6feb" />
+    Force&nbsp;reload
+  </label>
   <button id="prev-btn" onclick="stepEvent(-1)" disabled>◀ Prev</button>
   <button id="next-btn" onclick="stepEvent(+1)" disabled>Next ▶</button>
 </header>
@@ -244,6 +248,46 @@
   let eventList = [];        // populated from /device/events after connect
   let currentEventIndex = 0;
 
+  // ── DB mode: opened via ?db_id=<uuid>&api_base=<url> from History tab ────────
+  const _urlParams  = new URLSearchParams(window.location.search);
+  const _dbId       = _urlParams.get('db_id');
+  const _dbApiBase  = (_urlParams.get('api_base') || '').replace(/\/$/, '');
+
+  async function _loadFromDb() {
+    const apiBase = _dbApiBase || document.getElementById('api-base').value.replace(/\/$/, '');
+    setStatus('Loading waveform from database…', 'loading');
+    document.getElementById('unit-bar').style.display = 'none';
+    // Hide live-device controls — not relevant in DB mode
+    document.querySelector('header .conn-group').style.display = 'none';
+
+    const url = `${apiBase}/db/events/${encodeURIComponent(_dbId)}/waveform`;
+    let data;
+    try {
+      const resp = await fetch(url);
+      if (!resp.ok) {
+        const err = await resp.json().catch(() => ({ detail: resp.statusText }));
+        throw new Error(err.detail || resp.statusText);
+      }
+      data = await resp.json();
+    } catch (e) {
+      setStatus(`Error: ${e.message}`, 'error');
+      return;
+    }
+    lastData = data;
+    renderWaveform(data);
+  }
+
+  // Auto-load when opened with db_id param
+  window.addEventListener('DOMContentLoaded', () => {
+    if (_dbId) {
+      // Pre-fill api-base if provided
+      if (_dbApiBase) {
+        document.getElementById('api-base').value = _dbApiBase;
+      }
+      _loadFromDb();
+    }
+  });
+
   function setStatus(msg, cls = '') {
     const bar = document.getElementById('status-bar');
     bar.textContent = msg;
@@ -364,7 +408,8 @@
     btn.disabled = true;
     setStatus('Fetching waveform…', 'loading');
 
-    const url = `${apiBase}/device/event/${evIndex}/waveform?host=${encodeURIComponent(devHost)}&tcp_port=${tcpPort}`;
+    const force = document.getElementById('force-reload')?.checked ? '&force=true' : '';
+    const url = `${apiBase}/device/event/${evIndex}/waveform?host=${encodeURIComponent(devHost)}&tcp_port=${tcpPort}${force}`;
 
     let data;
     try {
@@ -404,8 +449,11 @@
     bar.innerHTML = '';
     bar.className = 'ok';
     const ts = data.timestamp;
-    if (ts) {
-      bar.textContent = `Event #${data.index}  —  ${ts.display}    `;
+    const tsDisplay = ts
+      ? (typeof ts === 'string' ? ts : (ts.display ?? JSON.stringify(ts)))
+      : null;
+    if (tsDisplay) {
+      bar.textContent = `Event #${data.index}  —  ${tsDisplay}    `;
     } else {
       bar.textContent = `Event #${data.index}    `;
     }
@@ -413,7 +461,14 @@
     appendMeta('sr', `${sr} sps`);
     appendMeta('samples', `${decoded.toLocaleString()} / ${total.toLocaleString()}`);
     appendMeta('pretrig', pretrig);
-    appendMeta('rectime', `${data.rectime_seconds ?? '?'}s`);
+    // rectime_seconds is computed from (total_samples - pretrig_samples) / sr in
+    // _decode_a5_waveform.  Also show the compliance config record_time for reference.
+    const cfgRt = unitInfo?.compliance_config?.record_time;
+    const strtRt = data.rectime_seconds;
+    const rtStr = (strtRt !== null && strtRt !== undefined)
+      ? `${strtRt}s (stored)` + (cfgRt !== null && cfgRt !== undefined ? ` / ${cfgRt}s (cfg)` : '')
+      : (cfgRt !== null && cfgRt !== undefined ? `${cfgRt}s (cfg)` : '?');
+    appendMeta('rectime', rtStr);
 
     // No waveform data — show a clear reason instead of empty charts
     if (decoded === 0) {
@@ -428,9 +483,14 @@
       return;
     }
 
-    // Build time axis (ms)
-    const times = Array.from({ length: decoded }, (_, i) =>
-      ((i - pretrig) / sr * 1000).toFixed(2)
+    // Clip to total_samples to exclude zero-padding the device appends beyond
+    // the configured record window.  total = pretrig + post_trig (e.g. 256+3072=3328).
+    // decoded may be larger (e.g. 4495) due to trailing zero-padded bulk-stream frames.
+    const displayCount = (total > 0 && total < decoded) ? total : decoded;
+
+    // Build time axis in seconds (matching Blastware event report layout).
+    const times = Array.from({ length: displayCount }, (_, i) =>
+      ((i - pretrig) / sr).toFixed(3)
     );
 
     // Show charts area
@@ -447,6 +507,13 @@
     const micPeakPsi = data.peak_values?.micl_psi ?? null;
     const DBL_REF_PSI = 2.9e-9; // 20 µPa in psi
 
+    // 0C record peak values (device-computed, authoritative) per channel
+    const peakValues0C = {
+      Tran: data.peak_values?.tran_in_s ?? null,
+      Vert: data.peak_values?.vert_in_s ?? null,
+      Long: data.peak_values?.long_in_s ?? null,
+    };
+
     for (const [ch, color] of Object.entries(CHANNEL_COLORS)) {
       const samples = channels[ch];
       if (!samples || samples.length === 0) continue;
@@ -455,22 +522,38 @@
       const isGeo = ch !== 'Mic';
       let plotSamples, peakLabel, yUnit, tooltipFmt, tickFmt;
 
+      // Clip channel samples to displayCount (same as time axis)
+      const clippedSamples = samples.length > displayCount
+        ? samples.slice(0, displayCount)
+        : samples;
+
+      // peak0C declared here (function scope) so it is visible in the Chart.js
+      // config block below (which lives outside the if(isGeo) block).
+      let peak0C = null;
+
       if (isGeo) {
         // Geo channels: counts × (range / 32767) → in/s
+        // Scale factor for the waveform shape (may need calibration per unit)
         const scale = geoRange / 32767;
-        plotSamples = samples.map(c => c * scale);
-        const peakIns = Math.max(...plotSamples.map(Math.abs));
+        plotSamples = clippedSamples.map(c => c * scale);
+
+        // Use the device-computed 0C record peak for the label (authoritative).
+        // The raw-sample-computed peak can be inflated by frame-boundary artifacts.
+        peak0C = peakValues0C[ch];
+        const peakIns = (peak0C !== null && peak0C !== undefined)
+          ? peak0C
+          : Math.max(...plotSamples.map(Math.abs));
         peakLabel  = `${peakIns.toFixed(5)} in/s`;
         yUnit      = 'in/s';
         tooltipFmt = v => `${ch}: ${v.toFixed(5)} in/s`;
         tickFmt    = v => v.toFixed(4);
       } else {
         // Mic: derive psi/count scale from the 0C peak value, display as psi; show dBL in header
-        const peakCounts = Math.max(...samples.map(Math.abs));
+        const peakCounts = Math.max(...clippedSamples.map(Math.abs));
         const micScale   = (micPeakPsi !== null && peakCounts > 0)
           ? Math.abs(micPeakPsi) / peakCounts
           : 1.0;
-        plotSamples = samples.map(c => c * micScale);
+        plotSamples = clippedSamples.map(c => c * micScale);
         const peakPsi = Math.max(...plotSamples.map(Math.abs));
         const peakDbl = peakPsi > 0 ? 20 * Math.log10(peakPsi / DBL_REF_PSI) : -Infinity;
         peakLabel  = `${peakDbl.toFixed(1)} dBL  (${peakPsi.toExponential(3)} psi)`;
@@ -504,7 +587,9 @@
         renderData  = plotSamples.filter((_, i) => i % step === 0);
       }
 
-      const chart = new Chart(canvas, {
+      let chart;
+      try {
+        chart = new Chart(canvas, {
           type: 'line',
           data: {
             labels: renderTimes,
@@ -526,7 +611,7 @@
                 mode: 'index',
                 intersect: false,
                 callbacks: {
-                title: items => `t = ${items[0].label} ms`,
+                  title: items => `t = ${items[0].label} s`,
                   label: item => tooltipFmt(item.raw),
                 },
               },
@@ -538,11 +623,21 @@
                   color: '#484f58',
                   maxTicksLimit: 10,
                   maxRotation: 0,
-                callback: (val, i) => renderTimes[i] + ' ms',
+                  callback: (val, i) => renderTimes[i] + ' s',
                 },
                 grid: { color: '#21262d' },
               },
               y: {
+                // Clamp geo-channel y-axis to ±(0C peak × 1.4) so near-saturation
+                // decode artifacts (which inflate autoscale to full range) don't
+                // squash the actual blast signal into an invisible flat line.
+                // The 0C peak value is authoritative for the true signal amplitude.
+                // Guard: only apply if peak0C is a valid finite positive number.
+                ...(isGeo && peak0C !== null && peak0C !== undefined
+                      && isFinite(peak0C) && peak0C > 0 ? {
+                  min: -(peak0C * 1.4),
+                  max:  (peak0C * 1.4),
+                } : {}),
                 ticks: {
                   color: '#484f58',
                   maxTicksLimit: 5,
@@ -566,7 +661,7 @@
               const xAxis = chart.scales.x;
               const yAxis = chart.scales.y;
 
-            // Find index of t=0
+              // Find index of the trigger point (t ≥ 0.000 s)
               const zeroIdx = renderTimes.findIndex(t => parseFloat(t) >= 0);
               if (zeroIdx < 0) return;
 
@@ -583,8 +678,12 @@
             },
           }],
         });
+      } catch (err) {
+        console.error(`Chart.js error for channel ${ch}:`, err);
+        canvasWrap.innerHTML = `<p style="color:#f85149;padding:8px;font-size:11px;">Chart error: ${err.message}</p>`;
+      }
 
-      charts[ch] = chart;
+      if (chart) charts[ch] = chart;
     }
   }