report_pdf: PDF histogram aggregation + fix footer/x-axis overlap

Two issues spotted on a histogram event PDF:

1. Footer scale ("Time — /div  Amplitude Geo: X in/s/div  Mic: Y
   psi(L)/div") was overlapping horizontally with the x-axis tick
   labels (0, 20, 40, 60...).  Both rendered on the same Y row.
   Fix: bumped gridspec bottom margin from 0.06 → 0.12, moved the
   footer text from y=0.045 → y=0.030 (below the tick labels), moved
   the page-bottom Created/Event line from y=0.015 → y=0.005.
   Trigger legend on waveforms moved 0.030 → 0.018.  Everything
   stacks cleanly now without collision.

2. PDF was showing the raw codec output (~150+ bars per histogram)
   instead of BW's per-interval aggregation.  Why: the aggregation
   I'd added to /db/events/{id}/waveform.json wasn't replicated in
   the PDF gather path.  Now: gather_report_data does the same
   max-per-group aggregation when bw_report.histogram.n_intervals is
   populated, AND derives per-interval HH:MM:SS labels from the
   start time + interval_size_s.  Result: histogram PDFs now match
   BW's display (one bar per BW interval, x-axis labeled with actual
   times) — same fix as the modal chart, applied to the PDF.

For events ingested BEFORE the parser extension (no histogram block
in their sidecar), aggregation is a no-op — they still render with
per-block bars + interval-index x-axis (but the overlap fix applies
to them too).  Re-forwarding repopulates the histogram block.

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

sfm/report_pdf.py

@@ -285,6 +285,43 @@ def gather_report_data(
         except Exception as exc:
             log.warning("gather_report_data: hdf5 read failed: %s", exc)
 
+    # ── Histogram aggregation ──
+    # Codec emits ~N per-block samples (typically 1/sec); BW reports
+    # one bar per configured interval (1 min / 5 min / etc.).  When
+    # bw_report.histogram.n_intervals is populated (events ingested
+    # with the parser extension), group max-per-group to match.  Also
+    # derives per-interval timestamps for the x-axis.  No-op for
+    # waveform events or when n_intervals is missing.
+    if rd.is_histogram and rd.histogram_n_intervals and rd.histogram_n_intervals >= 1:
+        n = int(rd.histogram_n_intervals)
+        for ch, vals in list(rd.channels.items()):
+            if not vals:
+                continue
+            per_group = len(vals) // n
+            remainder = len(vals) % n
+            agg: list = []
+            offset = 0
+            for i in range(n):
+                grp_size = per_group + (1 if i < remainder else 0)
+                if grp_size > 0:
+                    grp = vals[offset:offset + grp_size]
+                    agg.append(max((abs(v) for v in grp if v is not None), default=0))
+                    offset += grp_size
+                else:
+                    agg.append(0)
+            rd.channels[ch] = agg
+        # Derive per-interval HH:MM:SS labels if we have the start time + size
+        if rd.histogram_start_str and rd.histogram_interval_size_s and not rd.histogram_interval_times:
+            try:
+                import datetime as _dt
+                start = _dt.datetime.fromisoformat(rd.histogram_start_str)
+                rd.histogram_interval_times = [
+                    (start + _dt.timedelta(seconds=(i + 1) * rd.histogram_interval_size_s)).strftime("%H:%M:%S")
+                    for i in range(n)
+                ]
+            except Exception:
+                pass
+
     return rd
 
 
@@ -308,16 +345,18 @@ def render_event_report_pdf(rd: ReportData) -> bytes:
     else:
         _render_waveform_layout(fig, rd)
 
-    # Footer (common to both layouts) — Created date + Xmark-like attribution.
+    # Page footer (common to both layouts) — Created date + event id.
+    # Pushed to the very page bottom so it doesn't collide with the
+    # waveform footer scale / trigger legend lines just above.
     fig.text(
-        0.07, 0.015,
+        0.07, 0.005,
         f"Created: {rd.server_received_at or '—'}  •  seismo-relay",
-        fontsize=7, color="#888", ha="left",
+        fontsize=6, color="#888", ha="left",
     )
     fig.text(
-        0.93, 0.015,
+        0.93, 0.005,
         f"Event {rd.event_id[:8] if rd.event_id else '—'}",
-        fontsize=7, color="#888", ha="right",
+        fontsize=6, color="#888", ha="right",
     )
 
     buf = io.BytesIO()
@@ -331,10 +370,13 @@ def _render_waveform_layout(fig, rd: ReportData) -> None:
 
     Stats table includes Time (Rel. to Trig), Peak Accel, Peak Disp.
     Left margin sized to fit the channel labels (MicL/Long/Vert/Tran).
+    Extra bottom margin reserves space for x-axis tick labels +
+    "Amplitude Geo: X in/s/div Mic: Y psi(L)/div" footer + trigger
+    legend without overlap.
     """
     gs = fig.add_gridspec(
         nrows=4, ncols=1,
-        left=0.11, right=0.94, top=0.97, bottom=0.06,
+        left=0.11, right=0.94, top=0.97, bottom=0.12,
         height_ratios=[1.7, 2.0, 1.8, 5.5],
         hspace=0.35,
     )
@@ -355,11 +397,13 @@ def _render_histogram_layout(fig, rd: ReportData) -> None:
 
     No USBM compliance chart (it's a waveform-only concept).  Stats table
     uses Date + Time-of-peak instead of relative-time + accel + disp.
-    Left margin sized to fit the channel labels.
+    Left margin sized to fit the channel labels.  Extra bottom margin
+    leaves room for the x-axis time labels + footer scale legend
+    without overlap.
     """
     gs = fig.add_gridspec(
         nrows=4, ncols=1,
-        left=0.11, right=0.94, top=0.97, bottom=0.06,
+        left=0.11, right=0.94, top=0.97, bottom=0.12,
         height_ratios=[1.8, 0.9, 1.7, 5.6],
         hspace=0.35,
     )
@@ -718,12 +762,12 @@ def _draw_waveform_subplot(fig, gridspec_cell, rd: ReportData) -> None:
             geo_amp_div = f"{(amax * 1.1 * 2) / 10:.3f}"
             break
     fig.text(
-        0.07, 0.045,
+        0.11, 0.030,
         f"Time(Seconds) {div_s:.2f} sec/div   Amplitude Geo: {geo_amp_div} in/s/div   Mic: 0.001 psi(L)/div",
         fontsize=7, color="#444", ha="left",
     )
     fig.text(
-        0.07, 0.030,
+        0.11, 0.018,
         "Trigger = ▶━━━━━ ━━━━━━◀",
         fontsize=7, color="#444", ha="left",
     )
@@ -789,7 +833,7 @@ def _draw_histogram_subplot(fig, gridspec_cell, rd: ReportData) -> None:
             geo_amp_div = f"{amax / 5:.3f}"
             break
     fig.text(
-        0.07, 0.045,
+        0.11, 0.030,
         f"Time {interval_str} /div   Amplitude Geo: {geo_amp_div} in/s/div   Mic: 0.001 psi(L)/div",
         fontsize=7, color="#444", ha="left",
     )