backfill: overlay bw_report onto Event before DB upsert

Mirror what the ingest path does: BW's reported peaks (and sample_rate
/ record_time) take precedence over codec output where present.

Without this, --force backfill silently overwrites bw_report-overlaid
DB columns with codec-derived peaks.  Wrong for events where the codec
doesn't fully decode (waveform walker edge cases on SP0/SS0/SV0-style
events, histogram byte[5]!=0 sub-format that isn't yet RE'd), producing
PVS=0 on real high-amplitude events.  Bit on prod 2026-05-22 with
three top-10 waveform events ending up at PVS=0 (rolled back same day,
this fix is the proper resolution).

New helper minimateplus.event_file_io.apply_bw_report_dict_to_event
operates on the projected sidecar dict shape (the structure
_bw_report_to_dict produces, which is what gets preserved in the
sidecar).  Mirrors apply_report_to_event's semantics: only writes
fields where bw_report has a non-None value, no-ops cleanly on
empty / None input.

Dev validation against prod snapshot:
  pre  : 1839.7315 pvs_sum   356 events with DB PVS ≠ sidecar bw_report
  post : 2016.4902 pvs_sum     2 events still mismatched (both have NULL
                                timestamp + duplicate rows, edge case)

Both edge-case events DO get the correct value written by the new
backfill — their stale rows from prior backfills remain because
UNIQUE(serial, timestamp) doesn't fire on NULL.  Separate dedup
cleanup needed for those 2 events (0.014% of corpus); not blocking.

Backfill remains idempotent + bw_report preservation still passes
(0 WIPED, 0 CHANGED on the 3rd consecutive run).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_event_file_io.py

@@ -529,6 +529,77 @@ def test_save_imported_bw_round_trip(tmp_path: Path):
     assert stored_path.read_bytes() == src.read_bytes()
 
 
+# ── apply_bw_report_dict_to_event ────────────────────────────────────────────
+
+
+def test_apply_bw_report_dict_overlays_peaks_and_recording():
+    """Verbatim mirror of the data shape produced by `_bw_report_to_dict`
+    when projecting a parsed `BwAsciiReport` into the sidecar.  Confirms
+    each field overlays onto Event correctly so the backfill path
+    matches ingest behavior."""
+    from minimateplus.models import PeakValues
+    ev = Event(index=0)
+    bw_report = {
+        "peaks": {
+            "tran":       {"ppv_ips": 9.84375},
+            "vert":       {"ppv_ips": 0.305},
+            "long":       {"ppv_ips": 0.405},
+            "vector_sum": {"ips": 14.86736},
+        },
+        "mic": {"pspl_dbl": 115.9},
+        "recording": {"sample_rate_sps": 1024, "record_time_s": 3.0},
+    }
+    event_file_io.apply_bw_report_dict_to_event(ev, bw_report)
+    assert ev.peak_values is not None
+    assert ev.peak_values.tran             == 9.84375
+    assert ev.peak_values.vert             == 0.305
+    assert ev.peak_values.long             == 0.405
+    assert ev.peak_values.peak_vector_sum  == 14.86736
+    # MicL is converted dB → psi via _dbl_to_psi — just confirm non-zero
+    assert ev.peak_values.micl is not None and ev.peak_values.micl > 0
+    assert ev.sample_rate    == 1024
+    assert ev.rectime_seconds == 3.0
+
+
+def test_apply_bw_report_dict_overwrites_codec_peaks():
+    """The whole point of this helper: bw_report wins over whatever the
+    codec produced.  This is what the 2026-05-22 prod backfill missed —
+    DB peaks got overwritten with codec output (incl. PVS=0 on the
+    three top events) when they should have stayed bw_report-overlaid."""
+    from minimateplus.models import PeakValues
+    ev = Event(index=0)
+    # Simulate codec output that's clearly wrong (incomplete decode):
+    ev.peak_values = PeakValues(
+        tran=2.09, vert=0.0, long=0.0, peak_vector_sum=0.0,
+    )
+    bw_report = {
+        "peaks": {
+            "tran":       {"ppv_ips": 9.84},
+            "vert":       {"ppv_ips": 4.95},
+            "long":       {"ppv_ips": 8.05},
+            "vector_sum": {"ips": 14.95},
+        },
+    }
+    event_file_io.apply_bw_report_dict_to_event(ev, bw_report)
+    assert ev.peak_values.tran             == 9.84
+    assert ev.peak_values.vert             == 4.95
+    assert ev.peak_values.long             == 8.05
+    assert ev.peak_values.peak_vector_sum  == 14.95
+
+
+def test_apply_bw_report_dict_no_op_on_empty():
+    """None / empty dict / missing keys should leave Event untouched."""
+    from minimateplus.models import PeakValues
+    for empty in (None, {}, {"peaks": {}}, {"peaks": {"tran": {}}}):
+        ev = Event(index=0)
+        ev.peak_values = PeakValues(tran=1.0, vert=2.0, long=3.0)
+        event_file_io.apply_bw_report_dict_to_event(ev, empty)
+        # Unchanged
+        assert ev.peak_values.tran == 1.0
+        assert ev.peak_values.vert == 2.0
+        assert ev.peak_values.long == 3.0
+
+
 if __name__ == "__main__":
     if pytest is not None:
         pytest.main([__file__, "-v"])