feat: value history heatmap, write-fail guard, crash handler hardening

- Value history ring buffer (10 slots) tracks per-node change frequency
- Three-level heatmap: cold (blue), warm (amber), hot (red) via theme
- Heat persists indefinitely (no fade) — shows analysis history
- Calltip on hover shows previous values list
- Old themes auto-derive heat colors from existing palette
- Write failures no longer apply optimistic visual updates
- Crash handler: re-entrancy guard, context dump before risky APIs

src/themes/defaults/reclass_dark.json

@@ -22,6 +22,9 @@
     "indHoverSpan": "#E6B450",
     "indCmdPill": "#2a2a2a",
     "indDataChanged": "#8fbc7a",
+    "indHeatCold": "#569cd6",
+    "indHeatWarm": "#E6B450",
+    "indHeatHot": "#f44747",
     "indHintGreen": "#5a8248",
     "markerPtr": "#f44747",
     "markerCycle": "#e5a00d",

src/themes/defaults/vs.json

@@ -22,6 +22,9 @@
     "indHoverSpan": "#b180d7",
     "indCmdPill": "#2d2d30",
     "indDataChanged": "#8fbc7a",
+    "indHeatCold": "#569cd6",
+    "indHeatWarm": "#d69d85",
+    "indHeatHot": "#f44747",
     "indHintGreen": "#5a8248",
     "markerPtr": "#f44747",
     "markerCycle": "#e5a00d",

src/themes/defaults/warm.json

@@ -22,6 +22,9 @@
     "indHoverSpan": "#AA9565",
     "indCmdPill": "#2a2a2a",
     "indDataChanged": "#6B959F",
+    "indHeatCold": "#6B959F",
+    "indHeatWarm": "#AA9565",
+    "indHeatHot": "#A05040",
     "indHintGreen": "#464646",
     "markerPtr": "#6B3B21",
     "markerCycle": "#AA9565",

src/themes/theme.cpp

@@ -28,6 +28,9 @@ const ThemeFieldMeta kThemeFields[] = {
     {"indHoverSpan",  "Hover Span",     "Indicators",  &Theme::indHoverSpan},
     {"indCmdPill",    "Cmd Pill",       "Indicators",  &Theme::indCmdPill},
     {"indDataChanged","Data Changed",   "Indicators",  &Theme::indDataChanged},
+    {"indHeatCold",   "Heat Cold",      "Indicators",  &Theme::indHeatCold},
+    {"indHeatWarm",   "Heat Warm",      "Indicators",  &Theme::indHeatWarm},
+    {"indHeatHot",    "Heat Hot",       "Indicators",  &Theme::indHeatHot},
     {"indHintGreen",  "Hint Green",     "Indicators",  &Theme::indHintGreen},
     {"markerPtr",     "Pointer",        "Markers",     &Theme::markerPtr},
     {"markerCycle",   "Cycle",          "Markers",     &Theme::markerCycle},
@@ -50,6 +53,14 @@ Theme Theme::fromJson(const QJsonObject& o) {
         if (o.contains(kThemeFields[i].key))
             t.*kThemeFields[i].ptr = QColor(o[kThemeFields[i].key].toString());
     }
+    // Derive heat colors from the theme's own palette when keys are absent
+    // cold = keyword blue, warm = hover/string amber, hot = marker red
+    if (!t.indHeatCold.isValid())
+        t.indHeatCold = t.syntaxKeyword;
+    if (!t.indHeatWarm.isValid())
+        t.indHeatWarm = t.indHoverSpan.isValid() ? t.indHoverSpan : t.syntaxString;
+    if (!t.indHeatHot.isValid())
+        t.indHeatHot = t.markerPtr;
     return t;
 }
 

src/themes/theme.h

@@ -38,7 +38,10 @@ struct Theme {
     // ── Indicators ──
     QColor indHoverSpan;    // hover link text
     QColor indCmdPill;      // command row pill bg
-    QColor indDataChanged;  // changed data values
+    QColor indDataChanged;  // changed data values (legacy, fallback for old themes)
+    QColor indHeatCold;     // heatmap level 1 (changed once)
+    QColor indHeatWarm;     // heatmap level 2 (moderate changes)
+    QColor indHeatHot;      // heatmap level 3 (frequent changes)
     QColor indHintGreen;    // comment/hint text
 
     // ── Markers ──