feat(map): add peak highlights and live metrics to PNG export

- Draw rings around hottest and coldest sensors on export.
- Extend export_image to support second line for live metrics.
- Format detailed sensor stats in export footer.
- Add test coverage for footer rows, overlays, and stats.

src/pygui/ISC/Tabs/WaferMapTab.qml

@@ -203,8 +203,8 @@ Item {
                     id: readoutPanel
                     anchors.fill: parent
                     anchors.margins: 0
-                    onExportRequested: function(filePath) {
+                    onExportRequested: function(filePath, extra) {
-                        waferView.exportImage(filePath);
+                        waferView.exportImage(filePath, extra);
                     }
                 }
             }

src/pygui/ISC/Tabs/components/ReadoutPanel.qml

@@ -15,7 +15,7 @@ ColumnLayout {
     property alias heatmapBlend: heatmapSlider.value
     property alias showThickness: thicknessToggle.checked
 
-    signal exportRequested(string filePath)
+    signal exportRequested(string filePath, string extra)
 
     component PanelCheckBox: CheckBox {
         id: toggle
@@ -80,8 +80,8 @@ ColumnLayout {
 
     StreamControlPanel {
         Layout.fillWidth: true
-        onExportRequested: function(filePath) {
+        onExportRequested: function(filePath, extra) {
-            root.exportRequested(filePath);
+            root.exportRequested(filePath, extra);
         }
     }
 

src/pygui/ISC/Tabs/components/StreamControlPanel.qml

@@ -15,7 +15,7 @@ Rectangle {
     border.color: Theme.sideBorder
     border.width: 1
 
-    signal exportRequested(string filePath)
+    signal exportRequested(string filePath, string extra)
 
     property int _liveSecs: 0
     Connections {
@@ -310,7 +310,14 @@ Rectangle {
                 nameFilters: ["PNG files (*.png)"]
                 onAccepted: {
                     var path = String(selectedFile).replace(/^file:\/\//, "");
-                    root.exportRequested(path);
+                    var extra = "";
+                    if (streamController.mode === "live") {
+                        extra = "Frames: " + streamController.receivedCount
+                              + "   Errors: " + streamController.errorCount
+                              + "   Resyncs: " + streamController.resyncCount
+                              + "   Elapsed: " + root.fmtTime(root._liveSecs);
+                    }
+                    root.exportRequested(path, extra);
                 }
             }
         }

src/pygui/ISC/Tabs/components/WaferMapView.qml

@@ -58,7 +58,7 @@ Item {
         id: replaceDialog
     }
 
-    function exportImage(filePath) {
+    function exportImage(filePath, extra) {
-        return map.export_image(filePath);
+        return map.export_image(filePath, extra || "");
     }
 }

src/pygui/backend/visualization/wafer_map_item.py

@@ -27,6 +27,7 @@ from PySide6.QtGui import (
 from PySide6.QtQml import QmlElement
 from PySide6.QtQuick import QQuickPaintedItem
 
+from pygui.backend.models.frame_stats import compute_stats
 from pygui.backend.visualization.rbf_heatmap import (
     ellipse_alpha,
     interpolate_field,
@@ -36,6 +37,16 @@ from pygui.backend.wafer.zwafer_models import Sensor
 
 log = logging.getLogger(__name__)
 
+
+def readout_text(values: list[float]) -> str:
+    """Full READOUT stats line for the export footer; '' when no data."""
+    if not values:
+        return ""
+    s = compute_stats(values)
+    return (f"Sensors: {len(values)}   Min: {s.min:.2f}°C (#{s.min_index + 1})   "
+            f"Max: {s.max:.2f}°C (#{s.max_index + 1})   Diff: {s.diff:.2f}   "
+            f"Avg: {s.avg:.2f}   σ: {s.sigma:.2f}   3σ: {s.three_sigma:.2f}")
+
 QML_IMPORT_NAME = "ISC.Wafer"
 QML_IMPORT_MAJOR_VERSION = 1
 
@@ -301,11 +312,13 @@ class WaferMapItem(QQuickPaintedItem):
     #   chosen output dir, plus an optional summary CSV of (file, min/max/mean).
     #   No new rendering code needed — see docs/pending/alpha-release-polish-plan.md §6.1.
     @Slot(str, result=bool)
-    def export_image(self, file_path: str) -> bool:
+    @Slot(str, str, result=bool)
+    def export_image(self, file_path: str, extra: str = "") -> bool:
         """Export the current wafer map rendering to a PNG file
 
         Args:
-            file_pat: Absolute path for the output PNG.
+            file_path: Absolute path for the output PNG.
+            extra: Optional second footer line (live stream metrics).
 
         Returns:
         True on success, False on failure
@@ -321,33 +334,47 @@ class WaferMapItem(QQuickPaintedItem):
             w, h = int(self.width()), int(self.height())
             if w <= 0 or h <= 0:
                 return False
-            metrics = self._metrics_text()
+            lines = [ln for ln in (readout_text(self._values), extra) if ln]
-            footer_h = 28 if metrics else 0
+            footer_h = 28 * len(lines)
             img = QImage(w, h + footer_h, QImage.Format.Format_ARGB32)
             img.fill(0)  # transparent background
             painter = QPainter(img)
             self.paint(painter)
-            if metrics:
+            self._paint_extremes(painter)
-                footer = QRectF(0, h, w, footer_h)
+            if lines:
-                painter.fillRect(footer, QColor("#101014"))
+                painter.fillRect(QRectF(0, h, w, footer_h), QColor("#101014"))
                 painter.setPen(QColor("#CBD5E1"))
-                painter.drawText(footer, Qt.AlignmentFlag.AlignCenter, metrics)
+                for i, line in enumerate(lines):
+                    painter.drawText(QRectF(0, h + 28 * i, w, 28),
+                                     Qt.AlignmentFlag.AlignCenter, line)
             painter.end()
             return bool(img.save(file_path))
         except Exception as e:
             log.error("Export failed: %s", e)
             return False
 
-    def _metrics_text(self) -> str:
-        """One-line metric readout for the export footer; '' when no data."""
-        if not self._values:
-            return ""
-        vs = self._values
-        return (f"Sensors: {len(vs)}   Min: {min(vs):.2f}°C   "
-                f"Max: {max(vs):.2f}°C   Avg: {sum(vs) / len(vs):.2f}°C")
 
     # ── internal ─────────────────────────────────────────────────────────
 
+    def _paint_extremes(self, painter: QPainter) -> None:
+        """Ring the hottest (high color) and coldest (low color) markers.
+
+        Export-only overlay — paint() itself stays untouched so the live
+        view is unchanged.
+        """
+        if not self._values or not self._markers:
+            return
+        s = compute_stats(self._values)
+        ring_r = self._marker_r + 5
+        painter.setBrush(Qt.BrushStyle.NoBrush)
+        for idx, color in ((s.max_index, self._high_color),
+                           (s.min_index, self._low_color)):
+            if idx not in self._markers:
+                continue
+            px, py = self._markers[idx]
+            painter.setPen(QPen(color, 2))
+            painter.drawEllipse(px - ring_r, py - ring_r, 2 * ring_r, 2 * ring_r)
+
     def _rebuild_thickness(self) -> None:
         """Interpolate thickness data into a gray/orange heatmap QImage."""
         if not self._sensors or not self._thickness_data:

tests/test_wafer_map_item.py

@@ -111,6 +111,76 @@ def test_export_image_includes_metrics_footer(tmp_path):
     assert loaded.pixelColor(5, loaded.height() - 5).alpha() == 255
 
 
+def test_export_image_extra_line_grows_footer(tmp_path):
+    """Live export passes an extra metrics line; the footer gains a second
+    row for it. Review export (no extra) keeps the single-row footer."""
+    from PySide6.QtGui import QImage
+
+    from pygui.backend.visualization.wafer_map_item import WaferMapItem
+
+    item = WaferMapItem()
+    item.setWidth(200)
+    item.setHeight(200)
+    item.values = [10.0, 20.0, 30.0]
+
+    review = tmp_path / "review.png"
+    live = tmp_path / "live.png"
+    assert item.export_image(str(review)) is True
+    assert item.export_image(str(live), "Frames: 42   Errors: 0") is True
+
+    h_review = QImage(str(review)).height()
+    h_live = QImage(str(live)).height()
+    assert h_review > 200  # readout footer present
+    assert h_live > h_review  # extra live row appended
+
+
+def test_export_image_highlights_hottest_and_coldest(tmp_path):
+    """The exported map rings the hottest sensor in the high color and the
+    coldest in the low color. With no bands set every marker fill is the
+    in-range green, so any high/low-colored pixels must come from the rings."""
+    from PySide6.QtGui import QImage
+
+    from pygui.backend.visualization.wafer_map_item import WaferMapItem
+
+    item = WaferMapItem()
+    item.setWidth(200)
+    item.setHeight(200)
+    item.sensors = [
+        {"label": "1", "x": -50.0, "y": 0.0},
+        {"label": "2", "x": 0.0, "y": 0.0},
+        {"label": "3", "x": 50.0, "y": 0.0},
+    ]
+    item.values = [10.0, 20.0, 30.0]
+    out = tmp_path / "wafer.png"
+    assert item.export_image(str(out)) is True
+
+    img = QImage(str(out))
+    found = {img.pixelColor(x, y).name()
+             for y in range(img.height()) for x in range(img.width())}
+    assert "#ef4444" in found  # hottest ring (sensorHigh)
+    assert "#5b9df5" in found  # coldest ring (sensorLow)
+
+
+def test_readout_text_full_stats():
+    """Export footer readout carries every READOUT stat with sensor indices.
+
+    Worked example: [10, 20, 30] → min 10 (#1), max 30 (#3), diff 20,
+    avg 20, σ = sqrt(200/3) ≈ 8.16, 3σ ≈ 24.49.
+    """
+    from pygui.backend.visualization.wafer_map_item import readout_text
+
+    assert readout_text([10.0, 20.0, 30.0]) == (
+        "Sensors: 3   Min: 10.00°C (#1)   Max: 30.00°C (#3)   "
+        "Diff: 20.00   Avg: 20.00   σ: 8.16   3σ: 24.49"
+    )
+
+
+def test_readout_text_empty():
+    from pygui.backend.visualization.wafer_map_item import readout_text
+
+    assert readout_text([]) == ""
+
+
 def test_export_image_no_data_fails(tmp_path):
     """No file loaded / no stream played -> nothing meaningful to export."""
     from pygui.backend.visualization.wafer_map_item import WaferMapItem