debug: figuring out whats wrong with waveform viewer

CLAUDE.md

@@ -191,6 +191,14 @@ rectime_seconds = int(round((total_samples - pretrig_samples) / sample_rate))
 `_decode_a5_waveform` uses `sample_rate=1024` as a default; the server overrides with
 `compliance_config.sample_rate` when available.  Do NOT use `strt[18]` for rectime.
 
+**Sanity check — pretrig_samples must be less than total_samples:**
+If `pretrig_samples >= total_samples` the STRT parse is invalid.  Possible causes:
+DLE-stuffed `0x10` byte within prev_key4 or key4 shifted field offsets, or a different
+STRT record variant.  `_decode_a5_waveform` logs `raw strt[0:21]` at WARNING level and
+clamps `pretrig_samples = 0` so the viewer renders (showing the full waveform from t=0).
+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

minimateplus/client.py

@@ -1395,6 +1395,18 @@ def _decode_a5_waveform(
     total_samples   = struct.unpack_from(">H", strt, 14)[0]
     pretrig_samples = struct.unpack_from(">H", strt, 16)[0]
 
+    # Sanity check: pretrig must be less than total_samples.
+    # If not, the STRT layout is suspect (DLE-stuffing shift, different record variant, etc.).
+    # Log the raw bytes for diagnosis and clamp pretrig to 0 so the viewer renders.
+    if pretrig_samples >= total_samples:
+        log.warning(
+            "_decode_a5_waveform: pretrig_samples=%d >= total_samples=%d — "
+            "STRT layout suspect. Raw strt[0:21]: %s  "
+            "Clamping pretrig to 0 for rendering.",
+            pretrig_samples, total_samples, strt[0:21].hex(' '),
+        )
+        pretrig_samples = 0
+
     # strt[18] is a record-mode/type byte, NOT rectime in seconds.
     # Confirmed from analysis of 4-9-26 ACH capture (15 distinct events):
     #   flags=0xFFFE (single-shot) → strt[18]=0x46 ('F') for all events regardless of duration
@@ -1412,8 +1424,10 @@ def _decode_a5_waveform(
 
     log.debug(
         "_decode_a5_waveform: STRT total_samples=%d pretrig=%d "
-        "strt[18]=0x%02X (mode byte, not seconds) computed_rectime=%ds",
+        "strt[18]=0x%02X (mode byte, not seconds) computed_rectime=%ds  "
+        "raw strt[0:21]: %s",
         total_samples, pretrig_samples, strt[18], rectime_seconds,
+        strt[0:21].hex(' '),
     )
 
     # ── Collect per-frame waveform bytes with global offset tracking ─────────

sfm/waveform_viewer.html

@@ -573,7 +573,9 @@
         renderData  = plotSamples.filter((_, i) => i % step === 0);
       }
 
-      const chart = new Chart(canvas, {
+      let chart;
+      try {
+        chart = new Chart(canvas, {
           type: 'line',
           data: {
             labels: renderTimes,
@@ -616,7 +618,9 @@
                 // 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.
-              ...(isGeo && peak0C !== null && peak0C > 0 ? {
+                // 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),
                 } : {}),
@@ -660,8 +664,12 @@
             },
           }],
         });
+      } 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;
     }
   }