fix(decode): recover the exact waveform trigger from the binary (no .TXT)

Follow-up to the ts1→ts2 fix: get the trigger to the second from the binary
alone, instead of falling back to the stop time (~record-duration late) for
no-report events.

The configured post-trigger record time is a big-endian float32 in the
recording-setup config block, exactly 30 bytes before the "Standard Recording
Setup" marker.  _parse_record_time_seconds reads it; the waveform branch now
stamps trigger = ts2 - record_time.  Verified: the field reads 1.0 / 2.0 / 3.0 s
across different setups in the corpus, and all 7 BE12844 oracle events now
decode to their exact Blastware trigger (N844LQHB 10:33:29) from the binary,
no paired .TXT needed.  Falls back to ts2 (the stop) if the config block is
absent.  A paired report's event_datetime stays authoritative (clock drift).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YDXjZCr4RqT2U3QvMDhgzf

minimateplus/event_file_io.py

@@ -818,6 +818,30 @@ def derive_record_type_from_filename(filename, default: str = "Waveform") -> str
     return _RECORD_TYPE_BY_EXT_SUFFIX.get(ext[-1].upper(), default)
 
 
+# Marker for the recording-setup config block, and the offset of the record-time
+# float32 within it.  The configured post-trigger record time (seconds) is a
+# big-endian float32 exactly 30 bytes before the "Standard Recording Setup"
+# label.  Verified across the corpus reading 1.0 / 2.0 / 3.0 s on different
+# setups — and ts2 - record_time reproduces Blastware's trigger to the second
+# (N844LQHB: stop 10:33:32 - 3.0 = 10:33:29).
+_RECSETUP_MARKER = b"Standard Recording Setup"
+_RECTIME_OFFSET_BEFORE_MARKER = 30
+
+
+def _parse_record_time_seconds(raw: bytes) -> Optional[float]:
+    """The configured post-trigger record time in seconds, from the recording-
+    setup config block, or None when absent / implausible."""
+    a = raw.find(_RECSETUP_MARKER)
+    if a < _RECTIME_OFFSET_BEFORE_MARKER:
+        return None
+    off = a - _RECTIME_OFFSET_BEFORE_MARKER
+    try:
+        rt = struct.unpack(">f", raw[off:off + 4])[0]
+    except struct.error:
+        return None
+    return rt if 0.05 <= rt <= 600.0 else None
+
+
 def read_blastware_file(path: Union[str, Path]) -> Event:
     """
     Parse a Blastware waveform file into an Event.
@@ -966,22 +990,25 @@ def read_blastware_file(path: Union[str, Path]) -> Event:
     # record type:
     #   * Waveform: ts1 = the monitoring-SESSION start (shared across every
     #     event that day — a unit arming at 06:00 stamps 06:00 on all of them),
-    #     ts2 = THIS event's recording STOP.  ts2 is the correct binary-only
-    #     estimate of the event time; BW's displayed Date/Time is the trigger =
-    #     ts2 - record duration (~3 s), but the record-duration byte in the STRT
-    #     record is a misparsed record-type marker here (see the strt-build
-    #     note), so the exact trigger comes from the paired BW report's
-    #     event_datetime — apply_report_to_event() overrides with it when a
-    #     report is present.  (Stamping ts1 showed the session start, hours off.)
+    #     ts2 = THIS event's recording STOP.  Blastware's Date/Time is the
+    #     TRIGGER = ts2 - record time, and the record time is a float32 in the
+    #     recording-setup config block (see _parse_record_time_seconds), so the
+    #     exact trigger is recoverable from the binary alone.  Falls back to ts2
+    #     (the stop, within the record duration) if the config block is absent.
+    #     (Stamping ts1 showed the session start, hours off.)
     #   * Histogram / undecodable: ts1 = the window start, which IS the event
     #     time — keep it.
     # Discriminate by ``is_waveform_body`` (the codec), not the filename.
     if is_waveform_body and ts2 is not None:
+        _stop = datetime.datetime(ts2.year, ts2.month, ts2.day,
+                                  ts2.hour, ts2.minute, ts2.second)
+        _rt = _parse_record_time_seconds(raw)
+        _trig = _stop - datetime.timedelta(seconds=_rt) if _rt is not None else _stop
         ev.timestamp = Timestamp(
             raw=footer[10:18],
             flag=0x10,
-            year=ts2.year, unknown_byte=0, month=ts2.month, day=ts2.day,
-            hour=ts2.hour, minute=ts2.minute, second=ts2.second,
+            year=_trig.year, unknown_byte=0, month=_trig.month, day=_trig.day,
+            hour=_trig.hour, minute=_trig.minute, second=_trig.second,
         )
     elif ts1 is not None:
         ev.timestamp = Timestamp(