diff --git a/src/controller.cpp b/src/controller.cpp
index f1df75a..1a93c99 100644
--- a/src/controller.cpp
+++ b/src/controller.cpp
@@ -633,6 +633,52 @@ void RcxController::refresh() {
         }
     }
 
+    // Update value history and compute heat levels
+    // Use the snapshot provider if active; skip entirely if no valid provider
+    {
+        const Provider* prov = nullptr;
+        if (m_snapshotProv)
+            prov = m_snapshotProv.get();
+        else if (m_doc->provider && m_doc->provider->isValid())
+            prov = m_doc->provider.get();
+
+        if (prov) {
+            for (auto& lm : m_lastResult.meta) {
+                if (lm.nodeIdx < 0 || lm.nodeIdx >= m_doc->tree.nodes.size()) continue;
+                if (isSyntheticLine(lm) || lm.isContinuation) continue;
+                if (lm.lineKind != LineKind::Field) continue;
+
+                const Node& node = m_doc->tree.nodes[lm.nodeIdx];
+                // Skip containers — they don't have scalar values
+                if (node.kind == NodeKind::Struct || node.kind == NodeKind::Array) continue;
+                // Skip hex preview nodes — they show raw bytes, not a single value
+                if (isHexPreview(node.kind)) continue;
+
+                int64_t nodeOff = m_doc->tree.computeOffset(lm.nodeIdx);
+                uint64_t addr = m_doc->tree.baseAddress + static_cast<uint64_t>(nodeOff);
+                int sz = node.byteSize();
+                if (sz <= 0 || !prov->isReadable(addr, sz)) continue;
+
+                QString val = fmt::readValue(node, *prov, addr, lm.subLine);
+                if (!val.isEmpty()) {
+                    m_valueHistory[lm.nodeId].record(val);
+                    lm.heatLevel = m_valueHistory[lm.nodeId].heatLevel();
+                }
+            }
+        }
+
+        // Apply persisted heat levels even when provider is unavailable
+        if (!prov) {
+            for (auto& lm : m_lastResult.meta) {
+                if (lm.nodeId != 0) {
+                    auto it = m_valueHistory.find(lm.nodeId);
+                    if (it != m_valueHistory.end())
+                        lm.heatLevel = it->heatLevel();
+                }
+            }
+        }
+    }
+
     // Prune stale selections (nodes removed by undo/redo/delete)
     QSet<uint64_t> valid;
     for (uint64_t id : m_selIds) {
@@ -656,6 +702,7 @@ void RcxController::refresh() {
 
     for (auto* editor : m_editors) {
         editor->setCustomTypeNames(customTypes);
+        editor->setValueHistoryRef(&m_valueHistory);
         ViewState vs = editor->saveViewState();
         editor->applyDocument(m_lastResult);
         editor->restoreViewState(vs);
@@ -914,11 +961,13 @@ void RcxController::applyCommand(const Command& command, bool isUndo) {
                     int ai = tree.indexOfId(adj.nodeId);
                     if (ai >= 0) tree.nodes[ai].offset = adj.newOffset;
                 }
-                // Remove nodes
+                // Remove nodes and their value history
                 QVector<int> indices = tree.subtreeIndices(c.nodeId);
                 std::sort(indices.begin(), indices.end(), std::greater<int>());
-                for (int idx : indices)
+                for (int idx : indices) {
+                    m_valueHistory.remove(tree.nodes[idx].id);
                     tree.nodes.remove(idx);
+                }
                 tree.invalidateIdCache();
             }
         } else if constexpr (std::is_same_v<T, cmd::ChangeBase>) {
@@ -932,11 +981,14 @@ void RcxController::applyCommand(const Command& command, bool isUndo) {
             resetSnapshot();
         } else if constexpr (std::is_same_v<T, cmd::WriteBytes>) {
             const QByteArray& bytes = isUndo ? c.oldBytes : c.newBytes;
-            if (!m_doc->provider->writeBytes(c.addr, bytes))
+            // Write through snapshot (patches pages only on success) or provider directly.
+            // If write fails, the snapshot is NOT patched, so the next compose shows the
+            // real unchanged value — no optimistic visual leak.
+            bool ok = m_snapshotProv
+                ? m_snapshotProv->write(c.addr, bytes.constData(), bytes.size())
+                : m_doc->provider->writeBytes(c.addr, bytes);
+            if (!ok)
                 qWarning() << "WriteBytes failed at address" << QString::number(c.addr, 16);
-            // Patch snapshot so compose sees the new value immediately
-            if (m_snapshotProv)
-                m_snapshotProv->patchPages(c.addr, bytes.constData(), bytes.size());
         } else if constexpr (std::is_same_v<T, cmd::ChangeArrayMeta>) {
             int idx = tree.indexOfId(c.nodeId);
             if (idx >= 0) {
@@ -1019,8 +1071,21 @@ void RcxController::setNodeValue(int nodeIdx, int subLine, const QString& text,
     // Validate write range before pushing command
     if (!m_doc->provider->isReadable(addr, writeSize)) return;
 
+    // Read old bytes before writing (for undo)
     QByteArray oldBytes = m_doc->provider->readBytes(addr, writeSize);
 
+    // Test the write first — don't push a command that will silently fail.
+    // This prevents optimistic visual updates for read-only providers.
+    bool writeOk = m_snapshotProv
+        ? m_snapshotProv->write(addr, newBytes.constData(), newBytes.size())
+        : m_doc->provider->writeBytes(addr, newBytes);
+    if (!writeOk) {
+        qWarning() << "Write failed at address" << QString::number(addr, 16);
+        refresh();  // refresh to show the real unchanged value
+        return;
+    }
+
+    // Write succeeded — push undo command (redo will write again, which is harmless)
     m_doc->undoStack.push(new RcxCommand(this,
         cmd::WriteBytes{addr, oldBytes, newBytes}));
 }
@@ -2194,6 +2259,7 @@ void RcxController::resetSnapshot() {
     m_snapshotProv.reset();
     m_prevPages.clear();
     m_changedOffsets.clear();
+    m_valueHistory.clear();
 }
 
 void RcxController::handleMarginClick(RcxEditor* editor, int margin,
diff --git a/src/controller.h b/src/controller.h
index 865f09b..06d8a18 100644
--- a/src/controller.h
+++ b/src/controller.h
@@ -148,6 +148,7 @@ private:
     std::unique_ptr<SnapshotProvider> m_snapshotProv;
     PageMap         m_prevPages;
     QSet<int64_t>   m_changedOffsets;
+    QHash<uint64_t, ValueHistory> m_valueHistory;
     uint64_t        m_refreshGen = 0;
     uint64_t        m_readGen = 0;
     bool            m_readInFlight = false;
diff --git a/src/core.h b/src/core.h
index 9bd37ed..41f8316 100644
--- a/src/core.h
+++ b/src/core.h
@@ -8,6 +8,7 @@
 #include <QHash>
 #include <QSet>
 #include <cstdint>
+#include <array>
 #include <memory>
 #include <variant>
 
@@ -405,6 +406,49 @@ struct NodeTree {
 
 };
 
+// ── Value History (ring buffer for heatmap) ──
+
+struct ValueHistory {
+    static constexpr int kCapacity = 10;
+    std::array<QString, kCapacity> values;
+    int count = 0;   // total unique values recorded
+    int head  = 0;   // next write position in ring
+
+    void record(const QString& v) {
+        if (count > 0) {
+            int last = (head + kCapacity - 1) % kCapacity;
+            if (values[last] == v) return;  // no change
+        }
+        values[head] = v;
+        head = (head + 1) % kCapacity;
+        if (count < INT_MAX) count++;
+    }
+
+    int uniqueCount() const { return qMin(count, kCapacity); }
+
+    // 0=static, 1=cold(2 unique), 2=warm(3-4), 3=hot(5+)
+    int heatLevel() const {
+        if (count <= 1) return 0;
+        if (count == 2) return 1;
+        if (count <= 4) return 2;
+        return 3;
+    }
+
+    QString last() const {
+        if (count == 0) return {};
+        return values[(head + kCapacity - 1) % kCapacity];
+    }
+
+    // Iterate from oldest to newest (up to uniqueCount entries)
+    template<typename Fn>
+    void forEach(Fn&& fn) const {
+        int n = uniqueCount();
+        int start = (head + kCapacity - n) % kCapacity;
+        for (int i = 0; i < n; i++)
+            fn(values[(start + i) % kCapacity]);
+    }
+};
+
 // ── LineMeta ──
 
 enum class LineKind : uint8_t {
@@ -439,6 +483,7 @@ struct LineMeta {
     uint64_t offsetAddr     = 0;     // Raw absolute address (for margin toggle)
     uint32_t markerMask     = 0;
     bool     dataChanged    = false;  // true if any byte in this node changed since last refresh
+    int      heatLevel      = 0;     // 0=static, 1=cold, 2=warm, 3=hot (from ValueHistory)
     QVector<int> changedByteIndices;  // Hex preview: which byte indices (0-based) changed on this line
     int      lineByteCount  = 0;     // Hex preview: actual data byte count on this line
     int      effectiveTypeW = 14;  // Per-line type column width used for rendering
diff --git a/src/editor.cpp b/src/editor.cpp
index af50b0a..3d4345c 100644
--- a/src/editor.cpp
+++ b/src/editor.cpp
@@ -24,10 +24,12 @@ static constexpr int IND_HEX_DIM    = 9;
 static constexpr int IND_BASE_ADDR  = 10;  // Default text color override for command row address
 static constexpr int IND_HOVER_SPAN = 11;  // Blue text on hover (link-like)
 static constexpr int IND_CMD_PILL   = 12;  // Rounded chip behind command row spans
-static constexpr int IND_DATA_CHANGED = 13; // Amber text for changed data values
+static constexpr int IND_HEAT_COLD    = 13; // Heatmap level 1 (changed once)
 static constexpr int IND_CLASS_NAME   = 14; // Teal text for root class name
 static constexpr int IND_HINT_GREEN   = 15; // Green text for hint/comment text
 static constexpr int IND_LOCAL_OFF    = 16; // Dim text for inline local offset in relative mode
+static constexpr int IND_HEAT_WARM    = 17; // Heatmap level 2 (moderate changes)
+static constexpr int IND_HEAT_HOT     = 18; // Heatmap level 3 (frequent changes)
 
 static QString g_fontName = "JetBrains Mono";
 
@@ -161,9 +163,13 @@ void RcxEditor::setupScintilla() {
     m_sci->SendScintilla(QsciScintillaBase::SCI_INDICSETUNDER,
                          IND_CMD_PILL, (long)1);
 
-    // Data-changed indicator
+    // Heatmap indicators (cold / warm / hot)
     m_sci->SendScintilla(QsciScintillaBase::SCI_INDICSETSTYLE,
-                         IND_DATA_CHANGED, 17 /*INDIC_TEXTFORE*/);
+                         IND_HEAT_COLD, 17 /*INDIC_TEXTFORE*/);
+    m_sci->SendScintilla(QsciScintillaBase::SCI_INDICSETSTYLE,
+                         IND_HEAT_WARM, 17 /*INDIC_TEXTFORE*/);
+    m_sci->SendScintilla(QsciScintillaBase::SCI_INDICSETSTYLE,
+                         IND_HEAT_HOT, 17 /*INDIC_TEXTFORE*/);
 
     // Root class name — type color
     m_sci->SendScintilla(QsciScintillaBase::SCI_INDICSETSTYLE,
@@ -300,8 +306,13 @@ void RcxEditor::applyTheme(const Theme& theme) {
                          IND_HOVER_SPAN, theme.indHoverSpan);
     m_sci->SendScintilla(QsciScintillaBase::SCI_INDICSETFORE,
                          IND_CMD_PILL, theme.indCmdPill);
+    // Heatmap colors
     m_sci->SendScintilla(QsciScintillaBase::SCI_INDICSETFORE,
-                         IND_DATA_CHANGED, theme.indDataChanged);
+                         IND_HEAT_COLD, theme.indHeatCold);
+    m_sci->SendScintilla(QsciScintillaBase::SCI_INDICSETFORE,
+                         IND_HEAT_WARM, theme.indHeatWarm);
+    m_sci->SendScintilla(QsciScintillaBase::SCI_INDICSETFORE,
+                         IND_HEAT_HOT, theme.indHeatHot);
     m_sci->SendScintilla(QsciScintillaBase::SCI_INDICSETFORE,
                          IND_CLASS_NAME, theme.syntaxType);
     m_sci->SendScintilla(QsciScintillaBase::SCI_INDICSETFORE,
@@ -401,7 +412,7 @@ void RcxEditor::applyDocument(const ComposeResult& result) {
     applyMarkers(result.meta);
     applyFoldLevels(result.meta);
     applyHexDimming(result.meta);
-    applyDataChangedHighlight(result.meta);
+    applyHeatmapHighlight(result.meta);
     applyCommandRowPills();
 
     // Reset hint line - applySelectionOverlay will repaint indicators
@@ -765,35 +776,48 @@ static QString getLineText(QsciScintilla* sci, int line) {
     return text;
 }
 
-void RcxEditor::applyDataChangedHighlight(const QVector<LineMeta>& meta) {
-    for (int i = 0; i < meta.size(); i++) {
-        if (!meta[i].dataChanged) continue;
-        if (isSyntheticLine(meta[i])) continue;
+void RcxEditor::applyHeatmapHighlight(const QVector<LineMeta>& meta) {
+    static constexpr int heatIndicators[] = { IND_HEAT_COLD, IND_HEAT_WARM, IND_HEAT_HOT };
 
+    for (int i = 0; i < meta.size(); i++) {
         const LineMeta& lm = meta[i];
+        if (isSyntheticLine(lm)) continue;
+
+        int heat = lm.heatLevel;
         int typeW = lm.effectiveTypeW;
         int nameW = lm.effectiveNameW;
 
-        if (isHexPreview(lm.nodeKind) && !lm.changedByteIndices.isEmpty()) {
-            // Per-byte highlighting in ASCII + hex areas
+        // For hex preview nodes: use dataChanged + changedByteIndices (per-byte heat)
+        if (isHexPreview(lm.nodeKind) && lm.dataChanged && !lm.changedByteIndices.isEmpty()) {
+            // Hex nodes don't track heatLevel (they're skipped in controller).
+            // Use IND_HEAT_COLD for any changed byte (simple visual feedback).
             int ind = kFoldCol + lm.depth * 3;
             int asciiStart = ind + typeW + kSepWidth;
-            // ASCII column is padded to nameW (aligned with value column)
             int hexStart = asciiStart + nameW + kSepWidth;
 
             for (int byteIdx : lm.changedByteIndices) {
-                // Highlight in ASCII area (1 char per byte)
-                fillIndicatorCols(IND_DATA_CHANGED, i, asciiStart + byteIdx, asciiStart + byteIdx + 1);
-                // Highlight in hex area (2 hex chars per byte at position byteIdx*3)
+                fillIndicatorCols(IND_HEAT_COLD, i, asciiStart + byteIdx, asciiStart + byteIdx + 1);
                 int hexCol = hexStart + byteIdx * 3;
-                fillIndicatorCols(IND_DATA_CHANGED, i, hexCol, hexCol + 2);
+                fillIndicatorCols(IND_HEAT_COLD, i, hexCol, hexCol + 2);
             }
-        } else {
-            // Non-hex nodes: highlight entire value span
-            QString lineText = getLineText(m_sci, i);
-            ColumnSpan vs = valueSpan(lm, lineText.size(), typeW, nameW);
-            if (vs.valid)
-                fillIndicatorCols(IND_DATA_CHANGED, i, vs.start, vs.end);
+            continue;
+        }
+
+        // Non-hex nodes: apply heat-level indicator to value span
+        if (heat <= 0) continue;
+
+        QString lineText = getLineText(m_sci, i);
+        ColumnSpan vs = valueSpan(lm, lineText.size(), typeW, nameW);
+        if (!vs.valid) continue;
+
+        // Pick the right indicator for this heat level (1→cold, 2→warm, 3→hot)
+        int activeInd = heatIndicators[qBound(0, heat - 1, 2)];
+        fillIndicatorCols(activeInd, i, vs.start, vs.end);
+
+        // Clear the other two heat indicators on this span to avoid overlap
+        for (int hi : heatIndicators) {
+            if (hi != activeInd)
+                clearIndicatorLine(hi, i);
         }
     }
 }
@@ -2204,8 +2228,13 @@ void RcxEditor::applyHoverCursor() {
         return;
     }
 
-    // Mouse left viewport - set Arrow
+    // Mouse left viewport - set Arrow, cancel calltip
     if (!m_hoverInside) {
+        if (m_calltipVisible) {
+            m_sci->SendScintilla(QsciScintillaBase::SCI_CALLTIPCANCEL);
+            m_calltipVisible = false;
+            m_calltipLine = -1;
+        }
         m_sci->viewport()->setCursor(Qt::ArrowCursor);
         return;
     }
@@ -2294,6 +2323,43 @@ void RcxEditor::applyHoverCursor() {
         m_hoverSpanLines.append(h.line);
     }
 
+    // Value history calltip on hover
+    {
+        bool showCalltip = false;
+        if (m_valueHistory && h.line >= 0 && h.line < m_meta.size() && !m_editState.active) {
+            const LineMeta& lm = m_meta[h.line];
+            if (lm.heatLevel > 0 && lm.nodeId != 0) {
+                auto it = m_valueHistory->find(lm.nodeId);
+                if (it != m_valueHistory->end() && it->uniqueCount() > 1) {
+                    // Check cursor is over the value span
+                    QString lineText = getLineText(m_sci, h.line);
+                    ColumnSpan vs = valueSpan(lm, lineText.size(), lm.effectiveTypeW, lm.effectiveNameW);
+                    if (vs.valid && h.col >= vs.start && h.col < vs.end) {
+                        QString tip = QStringLiteral("Previous Values:");
+                        it->forEach([&](const QString& v) {
+                            tip += QStringLiteral("\n  ") + v;
+                        });
+                        if (m_calltipLine != h.line) {
+                            long pos = m_sci->SendScintilla(QsciScintillaBase::SCI_POSITIONFROMLINE,
+                                                            (unsigned long)h.line);
+                            QByteArray tipUtf8 = tip.toUtf8();
+                            m_sci->SendScintilla(QsciScintillaBase::SCI_CALLTIPSHOW,
+                                                 pos, tipUtf8.constData());
+                            m_calltipLine = h.line;
+                            m_calltipVisible = true;
+                        }
+                        showCalltip = true;
+                    }
+                }
+            }
+        }
+        if (!showCalltip && m_calltipVisible) {
+            m_sci->SendScintilla(QsciScintillaBase::SCI_CALLTIPCANCEL);
+            m_calltipVisible = false;
+            m_calltipLine = -1;
+        }
+    }
+
     // Determine cursor shape based on interaction type
     Qt::CursorShape desired = Qt::ArrowCursor;
 
diff --git a/src/editor.h b/src/editor.h
index c21f480..6b93a31 100644
--- a/src/editor.h
+++ b/src/editor.h
@@ -54,6 +54,7 @@ public:
     // Custom type names (struct types from the tree) shown in type picker + lexer GlobalClass coloring
     QString textWithMargins() const;
     void setCustomTypeNames(const QStringList& names);
+    void setValueHistoryRef(const QHash<uint64_t, ValueHistory>* ref) { m_valueHistory = ref; }
 
     // Saved sources for quick-switch in source picker
     void setSavedSources(const QVector<SavedSourceDisplay>& sources) { m_savedSourceDisplay = sources; }
@@ -129,6 +130,11 @@ private:
     // ── Saved sources for quick-switch ──
     QVector<SavedSourceDisplay> m_savedSourceDisplay;
 
+    // ── Value history ref (owned by controller) ──
+    const QHash<uint64_t, ValueHistory>* m_valueHistory = nullptr;
+    bool m_calltipVisible = false;
+    int  m_calltipLine = -1;
+
     // ── Reentrancy guards ──
     bool m_clampingSelection = false;
     bool m_updatingComment = false;
@@ -145,7 +151,7 @@ private:
     void applyMarkers(const QVector<LineMeta>& meta);
     void applyFoldLevels(const QVector<LineMeta>& meta);
     void applyHexDimming(const QVector<LineMeta>& meta);
-    void applyDataChangedHighlight(const QVector<LineMeta>& meta);
+    void applyHeatmapHighlight(const QVector<LineMeta>& meta);
     void applyBaseAddressColoring(const QVector<LineMeta>& meta);
     void applyCommandRowPills();
 
diff --git a/src/main.cpp b/src/main.cpp
index e4f0a7f..5a2f1b7 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -67,29 +67,56 @@ static void setDarkTitleBar(QWidget* widget) {
     }
 }
 
+// Guard flag to prevent re-entrant crash inside the handler
+static volatile LONG s_inCrashHandler = 0;
+
 static LONG WINAPI crashHandler(EXCEPTION_POINTERS* ep) {
+    // Prevent re-entrant crash: if we fault inside the handler, skip the
+    // risky dbghelp work and just terminate with what we already printed.
+    if (InterlockedCompareExchange(&s_inCrashHandler, 1, 0) != 0) {
+        fprintf(stderr, "\n(re-entrant fault inside crash handler — aborting)\n");
+        fflush(stderr);
+        return EXCEPTION_EXECUTE_HANDLER;
+    }
+
+    // Phase 1: always-safe output (no allocations, no complex APIs)
     fprintf(stderr, "\n=== UNHANDLED EXCEPTION ===\n");
     fprintf(stderr, "Code : 0x%08lX\n", ep->ExceptionRecord->ExceptionCode);
     fprintf(stderr, "Addr : %p\n", ep->ExceptionRecord->ExceptionAddress);
+#ifdef _M_X64
+    fprintf(stderr, "RIP  : 0x%016llx\n", (unsigned long long)ep->ContextRecord->Rip);
+    fprintf(stderr, "RSP  : 0x%016llx\n", (unsigned long long)ep->ContextRecord->Rsp);
+#else
+    fprintf(stderr, "EIP  : 0x%08lx\n", (unsigned long)ep->ContextRecord->Eip);
+#endif
+    fflush(stderr);
+
+    // Phase 2: attempt symbol resolution + stack walk
+    // Copy context so StackWalk64 can mutate it safely
+    CONTEXT ctxCopy = *ep->ContextRecord;
 
     HANDLE process = GetCurrentProcess();
     HANDLE thread  = GetCurrentThread();
-    SymSetOptions(SYMOPT_LOAD_LINES | SYMOPT_UNDNAME);
-    SymInitialize(process, NULL, TRUE);
+    SymSetOptions(SYMOPT_LOAD_LINES | SYMOPT_UNDNAME | SYMOPT_FAIL_CRITICAL_ERRORS);
+    if (!SymInitialize(process, NULL, TRUE)) {
+        fprintf(stderr, "\n(SymInitialize failed — no stack trace available)\n");
+        fprintf(stderr, "=== END CRASH ===\n");
+        fflush(stderr);
+        return EXCEPTION_EXECUTE_HANDLER;
+    }
 
-    CONTEXT* ctx = ep->ContextRecord;
     STACKFRAME64 frame = {};
     DWORD machineType;
 #ifdef _M_X64
     machineType = IMAGE_FILE_MACHINE_AMD64;
-    frame.AddrPC.Offset    = ctx->Rip;
-    frame.AddrFrame.Offset = ctx->Rbp;
-    frame.AddrStack.Offset = ctx->Rsp;
+    frame.AddrPC.Offset    = ctxCopy.Rip;
+    frame.AddrFrame.Offset = ctxCopy.Rbp;
+    frame.AddrStack.Offset = ctxCopy.Rsp;
 #else
     machineType = IMAGE_FILE_MACHINE_I386;
-    frame.AddrPC.Offset    = ctx->Eip;
-    frame.AddrFrame.Offset = ctx->Ebp;
-    frame.AddrStack.Offset = ctx->Esp;
+    frame.AddrPC.Offset    = ctxCopy.Eip;
+    frame.AddrFrame.Offset = ctxCopy.Ebp;
+    frame.AddrStack.Offset = ctxCopy.Esp;
 #endif
     frame.AddrPC.Mode    = AddrModeFlat;
     frame.AddrFrame.Mode = AddrModeFlat;
@@ -97,7 +124,7 @@ static LONG WINAPI crashHandler(EXCEPTION_POINTERS* ep) {
 
     fprintf(stderr, "\nStack trace:\n");
     for (int i = 0; i < 64; i++) {
-        if (!StackWalk64(machineType, process, thread, &frame, ctx,
+        if (!StackWalk64(machineType, process, thread, &frame, &ctxCopy,
                          NULL, SymFunctionTableAccess64,
                          SymGetModuleBase64, NULL))
             break;
diff --git a/src/themes/defaults/reclass_dark.json b/src/themes/defaults/reclass_dark.json
index 01d9d34..43aef87 100644
--- a/src/themes/defaults/reclass_dark.json
+++ b/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",
diff --git a/src/themes/defaults/vs.json b/src/themes/defaults/vs.json
index ab02d78..fa243da 100644
--- a/src/themes/defaults/vs.json
+++ b/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",
diff --git a/src/themes/defaults/warm.json b/src/themes/defaults/warm.json
index d6028e9..0f50e58 100644
--- a/src/themes/defaults/warm.json
+++ b/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",
diff --git a/src/themes/theme.cpp b/src/themes/theme.cpp
index e97750e..e2d58c1 100644
--- a/src/themes/theme.cpp
+++ b/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;
 }
 
diff --git a/src/themes/theme.h b/src/themes/theme.h
index 6cb7234..19db895 100644
--- a/src/themes/theme.h
+++ b/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 ──
diff --git a/tests/test_core.cpp b/tests/test_core.cpp
index 1d0eaa5..cc7a300 100644
--- a/tests/test_core.cpp
+++ b/tests/test_core.cpp
@@ -583,6 +583,94 @@ private slots:
         QCOMPARE(norm.size(), 1);
         QVERIFY(norm.contains(rootId));
     }
+
+    // ── ValueHistory tests ──
+
+    void testValueHistory_empty() {
+        rcx::ValueHistory h;
+        QCOMPARE(h.heatLevel(), 0);
+        QCOMPARE(h.uniqueCount(), 0);
+        QCOMPARE(h.last(), QString());
+    }
+
+    void testValueHistory_singleValue() {
+        rcx::ValueHistory h;
+        h.record("42");
+        QCOMPARE(h.heatLevel(), 0);  // only 1 unique → static
+        QCOMPARE(h.uniqueCount(), 1);
+        QCOMPARE(h.last(), QString("42"));
+    }
+
+    void testValueHistory_duplicateIgnored() {
+        rcx::ValueHistory h;
+        h.record("42");
+        h.record("42");
+        h.record("42");
+        QCOMPARE(h.count, 1);
+        QCOMPARE(h.heatLevel(), 0);
+    }
+
+    void testValueHistory_heatLevels() {
+        rcx::ValueHistory h;
+        h.record("a");
+        QCOMPARE(h.heatLevel(), 0);  // 1 unique
+
+        h.record("b");
+        QCOMPARE(h.heatLevel(), 1);  // 2 unique → cold
+
+        h.record("c");
+        QCOMPARE(h.heatLevel(), 2);  // 3 unique → warm
+
+        h.record("d");
+        QCOMPARE(h.heatLevel(), 2);  // 4 unique → warm
+
+        h.record("e");
+        QCOMPARE(h.heatLevel(), 3);  // 5 unique → hot
+    }
+
+    void testValueHistory_ringWrap() {
+        rcx::ValueHistory h;
+        // Fill beyond capacity
+        for (int i = 0; i < 15; i++)
+            h.record(QString::number(i));
+
+        QCOMPARE(h.count, 15);
+        QCOMPARE(h.uniqueCount(), 10);  // capped at kCapacity
+        QCOMPARE(h.heatLevel(), 3);     // hot
+        QCOMPARE(h.last(), QString("14"));
+
+        // Verify oldest values were pushed out, newest 10 remain
+        QStringList collected;
+        h.forEach([&](const QString& v) { collected.append(v); });
+        QCOMPARE(collected.size(), 10);
+        QCOMPARE(collected.first(), QString("5"));   // oldest surviving
+        QCOMPARE(collected.last(), QString("14"));    // newest
+    }
+
+    void testValueHistory_forEach() {
+        rcx::ValueHistory h;
+        h.record("x");
+        h.record("y");
+        h.record("z");
+
+        QStringList items;
+        h.forEach([&](const QString& v) { items.append(v); });
+        QCOMPARE(items.size(), 3);
+        QCOMPARE(items[0], QString("x"));
+        QCOMPARE(items[1], QString("y"));
+        QCOMPARE(items[2], QString("z"));
+    }
+
+    void testValueHistory_oscillation() {
+        // Values that oscillate (A → B → A → B) should still count each unique transition
+        rcx::ValueHistory h;
+        h.record("A");
+        h.record("B");
+        h.record("A");
+        h.record("B");
+        QCOMPARE(h.count, 4);       // 4 transitions
+        QCOMPARE(h.heatLevel(), 2); // warm (count=4 → 3-4 range)
+    }
 };
 
 QTEST_MAIN(TestCore)