fix(decode): stamp waveform events with the event time, not the session start

read_blastware_file built ev.timestamp from footer ts1, which for a WAVEFORM is
the monitoring-session start (a unit arming at 06:00 stamps 06:00 on every event
that day) — so every waveform's time was hours off (vomit-list #3, "~4.5 h off").
The event time is footer ts2 (the recording stop); BW's displayed Date/Time is
the trigger = ts2 - record duration.

Root cause proven against the BE12844 oracle set: 5 of 7 events decoded to the
identical 06:00:13 (the shared session start); ts2 gives distinct plausible
event times (N844LQHB ts2 = 10:33:32, BW trigger 10:33:29 = ts2 - 3.0 s rectime).

  * read_blastware_file now uses ts2 for waveforms (discriminated by which codec
    decoded the body, not the filename — save_imported_bw passes a tmp name).
    Histograms keep ts1 (the ~24 h window start, which IS the event time).
  * Binary-only decode can't get the exact trigger: the STRT record-time byte is
    a misparsed record-type marker (0x46=70), so ts2 (the stop, ~record duration
    after the trigger) is the best estimate. A paired BW report carries the exact
    trigger — apply_report_to_event now overlays event.timestamp from
    report.event_datetime, matching the existing build-path override (line ~441).

Tests: waveform → ts2, histogram → ts1 unchanged, report → exact trigger.

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

tests/test_event_timestamp.py

@@ -0,0 +1,53 @@
+"""Event timestamp decode — waveform trigger/stop vs histogram window start.
+
+The Blastware footer holds two timestamps: ts1 = footer[2:10], ts2 = footer[10:18].
+Their meaning depends on record type:
+
+  * Waveform: ts1 is the monitoring-SESSION start (e.g. 06:00 for a unit that
+    arms at 06:00 daily — shared across every event that day), and ts2 is THIS
+    event's recording STOP.  read_blastware_file used to stamp events with ts1 →
+    every waveform showed the session start (~4.5 h off).  Binary-only, the best
+    estimate is ts2 (the stop); the exact trigger BW displays (= ts2 - record
+    duration) comes from the paired report's event_datetime, since the binary
+    STRT record-time byte is a misparsed record-type marker.
+  * Histogram: ts1/ts2 are the ~24 h window [start, stop]; the event time is the
+    window start = ts1 (unchanged).
+"""
+import datetime
+from pathlib import Path
+
+from minimateplus.event_file_io import read_blastware_file, apply_report_to_event
+from minimateplus.bw_ascii_report import BwAsciiReport
+from minimateplus.models import Event
+
+FIX = Path(__file__).parent / "fixtures"
+WAVEFORM = FIX / "fft-oracle-2026-09-14" / "N844LQHB.ZT0W"   # footer ts2 = 2026-08-25 10:33:32
+HISTOGRAM = FIX / "ts-fix" / "K441LKZU.C30H"                 # window start 2026-05-10 19:04:50
+
+
+def _tuple(ts):
+    return (ts.year, ts.month, ts.day, ts.hour, ts.minute, ts.second)
+
+
+def test_waveform_timestamp_is_event_stop_not_session_start():
+    ev = read_blastware_file(WAVEFORM)
+    # ts2 (the event's recording stop), NOT the 06:00:13 monitoring-session
+    # start the old decode used.
+    assert _tuple(ev.timestamp) == (2026, 8, 25, 10, 33, 32), _tuple(ev.timestamp)
+
+
+def test_histogram_timestamp_is_window_start_unchanged():
+    ev = read_blastware_file(HISTOGRAM)
+    # Histogram event time = the window start (ts1); must NOT get the waveform
+    # ts2 treatment (that would land ~24 h off).
+    assert _tuple(ev.timestamp) == (2026, 5, 10, 19, 4, 50), _tuple(ev.timestamp)
+
+
+def test_report_event_datetime_overrides_to_exact_trigger():
+    # A paired BW report carries the exact trigger time; applying it must
+    # override the binary footer's stop time so the event matches BW exactly.
+    ev = read_blastware_file(WAVEFORM)
+    assert _tuple(ev.timestamp) == (2026, 8, 25, 10, 33, 32)   # stop, pre-report
+    apply_report_to_event(ev, BwAsciiReport(
+        event_datetime=datetime.datetime(2026, 8, 25, 10, 33, 29)))
+    assert _tuple(ev.timestamp) == (2026, 8, 25, 10, 33, 29)   # exact BW trigger