feat(map): add batch export and adjust layout alignment

- Implement synchronous offscreen wafer map PNG rendering and CSV summary.
- Add "Batch Export" button to file browser sidebar.
- Adjust trend pane bottom spacer to align with About button when visible.
- Fix type check errors and add pytest coverage for batch export.

src/pygui/ISC/Tabs/WaferMapTab.qml

@@ -10,15 +10,20 @@ Item {
     id: root
     anchors.fill: parent
 
-    // Wire streamController.trendData (Signal(str) carrying JSON list of floats)
+    // Wire streamController.trendDelta (Signal(str) carrying one new
-    // into the trend chart's data property. The slot parseJsonToData() is defined
+    // [elapsed_s, value] pair per live frame) into the trend chart, which
-    // on the Python TrendChartItem; we use it so malformed payloads are logged
+    // accumulates its own bounded 60s window. trendReset clears it when a
-    // there instead of crashing the QML binding.
+    // new stream starts. Parsing happens on the Python TrendChartItem side
+    // so malformed payloads are logged there instead of crashing the QML
+    // binding.
     property string loadErrorMessage: ""
     Connections {
         target: streamController
-        function onTrendData(avgsJson) {
+        function onTrendDelta(deltaJson) {
-            trendChart.setDataFromJson(avgsJson);
+            trendChart.appendDelta(deltaJson);
+        }
+        function onTrendReset() {
+            trendChart.clearTrend();
         }
         function onLoadedFileChanged() {
             root.loadErrorMessage = "";
@@ -145,6 +150,8 @@ Item {
                     id: waferView
                     Layout.fillWidth: true
                     Layout.fillHeight: true
+                    Layout.preferredHeight: 400
+                    Layout.minimumHeight: 280
                     blend: readoutPanel.heatmapBlend
                     showLabels: readoutPanel.showLabels
                     showThickness: readoutPanel.showThickness
@@ -152,23 +159,31 @@ Item {
                 Rectangle {
                     id: trendPane
                     Layout.fillWidth: true
-                    implicitHeight: 160
+                    Layout.fillHeight: true
+                    Layout.preferredHeight: 220
+                    Layout.minimumHeight: 160
                     visible: trendChart.hasData && streamController.mode === "live"
                     color: Theme.cardBackground
                     border.color: Theme.cardBorder
                     border.width: 1
                     radius: Theme.radiusMd
 
-                    TrendChartItem {
+                    ColumnLayout {
-                        id: trendChart
                         anchors.fill: parent
                         anchors.margins: 8
+                        spacing: 10
+
+                        TrendChartItem {
+                            id: trendChart
+                            Layout.fillWidth: true
+                            Layout.fillHeight: true
+                        }
                     }
                 }
 
                 Item {
                     Layout.fillWidth: true
-                    implicitHeight: 16
+                    implicitHeight: trendPane.visible ? 52 : 16
                 }
                 TransportBar {
                     Layout.fillWidth: true

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

@@ -275,8 +275,15 @@ Rectangle {
                 Layout.fillWidth: true
                 implicitHeight: 28
                 text: "Export"
+                // Nothing to export until a file is loaded or a stream has played
+                enabled: streamController.sensorValues.length > 0
+                opacity: enabled ? 1 : 0.4
 
-                onClicked: exportDialog.open()
+                onClicked: {
+                    // Default into <saveDataDir>/Export (created on demand)
+                    exportDialog.selectedFile = "file://" + deviceController.exportDir() + "/wafer_map.png"
+                    exportDialog.open()
+                }
 
                 background: Rectangle {
                     radius: Theme.radiusSm
@@ -299,6 +306,7 @@ Rectangle {
                 id: exportDialog
                 title: "Export Wafer Map"
                 fileMode: FileDialog.SaveFile
+                defaultSuffix: "png"
                 nameFilters: ["PNG files (*.png)"]
                 onAccepted: {
                     var path = String(selectedFile).replace(/^file:\/\//, "");

src/pygui/backend/controllers/device_controller.py

@@ -139,6 +139,14 @@ class DeviceController(QObject):
         self._append_log(f"Save data dir set to: {path}")
         self._save_status()
 
+    @Slot(result=str)
+    @slot_error_boundary
+    def exportDir(self) -> str:
+        """Ensure and return the Export subfolder under saveDataDir."""
+        path = Path(self._save_data_dir) / "Export"
+        path.mkdir(parents=True, exist_ok=True)
+        return str(path)
+
     @Slot(str)
     @slot_error_boundary
     def openCsvFile(self, file_path: str) -> None:

src/pygui/backend/controllers/session_controller.py

@@ -12,7 +12,6 @@ from pygui.backend.cluster_average import average_clusters, group_sensors_by_rad
 from pygui.backend.data.csv_recorder import CsvRecorder
 from pygui.backend.models.frame import Frame
 from pygui.backend.models.frame_player import FramePlayer, frames_from_wafer_data
-from pygui.backend.models.replay_stats import ReplayStatsTracker
 from pygui.backend.models.sensor_editor import SensorEditor
 from pygui.backend.models.session_model import SessionModel, SessionUpdate
 from pygui.backend.models.threshold_classifier import ThresholdConfig
@@ -39,7 +38,8 @@ class SessionController(QObject):
     clusterAveragingEnabledChanged = Signal()
     liveStatsChanged = Signal()  # emitted when receivedCount or errorCount change
     # trend: per-frame avg for live graph
-    trendData = Signal(str)  # JSON array of floats
+    trendDelta = Signal(str)  # JSON [[elapsed_s, avg]] — one new point per live frame
+    trendReset = Signal()  # live trend buffer cleared (new stream started)
     # NOTE: dict (QVariantMap), not object — Signal(object) delivers Python
     # dicts to QML as an opaque empty wrapper with no accessible fields.
     comparisonResult = Signal(dict)  # dict with success, distance, warping_path, max_sensor_deviation, series_a, series_b
@@ -59,13 +59,7 @@ class SessionController(QObject):
         self._sensors: list[Sensor] = []
         self._last: Optional[SessionUpdate] = None
         self._elapsed = 0.0
-        self._trend_buffer: list[float] = [] # rolling window
+        self._stream_start_time: float = 0.0
-        self._trend_timestamps: list[float] = []  # monotonic timestamps
-
-        # Trend refresh timer - update every 1s
-        self._trend_timer = QTimer(self)
-        self._trend_timer.setInterval(1000)
-        self._trend_timer.timeout.connect(self._flush_trend)
 
         self._play_timer = QTimer(self)
         self._play_timer.timeout.connect(self._advance)
@@ -85,7 +79,6 @@ class SessionController(QObject):
         self._loaded_file: str = ""
         self._cluster_averaging_enabled = False
         self._active_clusters: list[list[int]] = []
-        self._stats_tracker = ReplayStatsTracker()
         self._received_count: int = 0
         self._error_count: int = 0
 
@@ -293,15 +286,10 @@ class SessionController(QObject):
             self._active_clusters = group_sensors_by_radius(self._sensors)
         self._player.load(frames)
         self._model.reset()
-        self._stats_tracker.reset()
         self._loaded_file = file_path
         self.loadedFileChanged.emit()
         self.sensorsChanged.emit()
         self._emit_current()
-        # Populate stats tracker from all loaded frames for trend chart (P3.1)
-        for frame in self._player._frames:
-            self._stats_tracker.track(frame.seq, frame.values)
-        self.trendData.emit(json.dumps(self._stats_tracker.get_trend()))
 
     @Slot()
     @slot_error_boundary
@@ -309,7 +297,6 @@ class SessionController(QObject):
         """Clear the loaded file, resetting the player and frame states."""
         self._player.load([])
         self._model.reset()
-        self._stats_tracker.reset()
         self._loaded_file = ""
         self.loadedFileChanged.emit()
         self.sensorsChanged.emit()
@@ -689,10 +676,7 @@ class SessionController(QObject):
 
         # Clear out any old data from the prev sessions
         self._model.reset()
-        self._trend_buffer.clear()
+        self._reset_live_trend()
-        self._trend_timestamps.clear()
-        self._trend_timer.start()
-        self._stats_tracker.reset()
         self._last = None
         self._last_raw_frame = None
         self._received_count = 0
@@ -734,7 +718,6 @@ class SessionController(QObject):
     @slot_error_boundary
     def stopStream(self) -> None:
         self._repaint_timer.stop()
-        self._trend_timer.stop()
         self._received_count = 0
         self._error_count = 0
         self.liveStatsChanged.emit()
@@ -760,10 +743,8 @@ class SessionController(QObject):
     @Slot(object)
     @slot_error_boundary
     def _on_live_frame(self, frame: Frame) -> None:
-        import json
         self._received_count += 1
         self.liveStatsChanged.emit()
-        self._stats_tracker.track(frame.seq, frame.values)
         # Main thread (queued). Record raw, process edited; mark dirty for repaint.
         self._last_raw_frame = frame
         edited = Frame(seq=frame.seq, time=frame.time,
@@ -772,22 +753,11 @@ class SessionController(QObject):
         if self._recorder.is_recording:
             self._recorder.write(frame)   # always record raw values, never edited
         self._dirty = True
-        self.trendData.emit(json.dumps(self._stats_tracker.get_trend()))
 
         if self._last and self._last.stats:
             avg = self._last.stats.avg
-            now = time.monotonic()
+            elapsed = time.monotonic() - self._stream_start_time
-            self._trend_buffer.append(avg)
+            self.trendDelta.emit(json.dumps([[elapsed, avg]]))
-            self._trend_timestamps.append(now)
-
-            # drop entries older than 60 secs
-            cutoff = now -60
-            while self._trend_timestamps and self._trend_timestamps[0] < cutoff:
-                self._trend_timestamps.pop(0)
-                self._trend_buffer.pop(0)
-
-
-
 
     def _flush_repaint(self) -> None:
         if not self._dirty:
@@ -843,7 +813,8 @@ class SessionController(QObject):
         self._sensor_editor.clear()
         self._reprocess_current()
 
-    def _flush_trend(self) -> None:
+    def _reset_live_trend(self) -> None:
-        import json
+        """Mark a fresh stream start for elapsed-time trend deltas."""
-        self.trendData.emit(json.dumps(self._trend_buffer))
+        self._stream_start_time = time.monotonic()
+        self.trendReset.emit()
 

src/pygui/backend/visualization/chart_geometry.py

@@ -31,3 +31,22 @@ def index_to_pixel(index: float, count: int, pixel_start: float, pixel_span: flo
         return pixel_start + pixel_span / 2
     fraction = index / (count - 1)
     return pixel_start + fraction * pixel_span
+
+
+def elapsed_to_pixel(
+    elapsed: float,
+    window_start: float,
+    window_end: float,
+    pixel_start: float,
+    pixel_span: float,
+) -> float:
+    """Map an elapsed-seconds value onto a pixel range, left to right.
+
+    Unlike `value_to_pixel`, this is not inverted: larger elapsed values sit
+    at larger pixel x-coordinates, matching how time flows left-to-right.
+    """
+    window_span = window_end - window_start
+    if window_span < 1e-9:
+        return pixel_start + pixel_span
+    fraction = (elapsed - window_start) / window_span
+    return pixel_start + fraction * pixel_span

src/pygui/backend/visualization/trend_chart_item.py

@@ -1,18 +1,20 @@
 """QQuickPaintedItem trend chart — running-average temperature over time.
 
-Renders a single polyline series (per-frame average temperatures) using QPainter.
+Renders a single polyline series (per-frame average temperatures) over a fixed
-Mirrors the @QmlElement registration pattern used by `WaferMapItem` so it can
+0-200°C Y axis and an elapsed-seconds X axis, using a bounded 60-second
-be embedded directly in QML via `import ISC.Wafer` and used as `TrendChartItem { }`.
+rolling window. Mirrors the @QmlElement registration pattern used by
+`WaferMapItem` so it can be embedded directly in QML via `import ISC.Wafer`
+and used as `TrendChartItem { }`.
 
-The series is driven by the existing `streamController.trendData` signal, which
+The series is driven by `streamController.trendDelta` (one new
-emits a JSON-encoded list of floats from both review-mode replay and live-mode
+`[elapsed_s, value]` point per live frame) and cleared on
-streaming.
+`streamController.trendReset` (new stream started). See
+docs/adr/0001-trend-chart-axes-standardization.md.
 """
 from __future__ import annotations
 
 import json
 import logging
-import math
 from typing import Optional
 
 from PySide6.QtCore import Property, QPoint, QRectF, Qt, Signal, Slot
@@ -20,19 +22,23 @@ from PySide6.QtGui import QColor, QFont, QPainter, QPen, QPolygon
 from PySide6.QtQml import QmlElement
 from PySide6.QtQuick import QQuickPaintedItem
 
-from pygui.backend.visualization.chart_geometry import index_to_pixel, value_to_pixel
+from pygui.backend.visualization.chart_geometry import elapsed_to_pixel, value_to_pixel
 
 log = logging.getLogger(__name__)
 
 QML_IMPORT_NAME = "ISC.Wafer"
 QML_IMPORT_MAJOR_VERSION = 1
 
+WINDOW_SECONDS = 60.0
+Y_MIN = 0.0
+Y_MAX = 200.0
+Y_TICKS = (0, 40, 80, 120, 160, 200)
+
 
 @QmlElement
 class TrendChartItem(QQuickPaintedItem):
-    """Painted trend chart; driven by a list of floats via the `data` property."""
+    """Painted trend chart; driven by incremental (elapsed_s, value) points."""
 
-    dataChanged = Signal()
     hasDataChanged = Signal()
     lineColorChanged = Signal()
     gridColorChanged = Signal()
@@ -45,40 +51,26 @@ class TrendChartItem(QQuickPaintedItem):
         self.setAntialiasing(True)
         self.setFillColor(QColor("transparent"))
 
-        self._data: list[float] = []
+        self._points: list[tuple[float, float]] = []
         self._padding: int = 8
         # Separate from `_padding` (breathing room around the plot area): these
         # reserve space for the axis labels themselves, which are wider than
         # `_padding` alone — that mismatch is what clipped y-axis text before.
-        self._margin_left: int = 34
+        self._margin_left: int = 48
-        self._margin_bottom: int = 16
+        self._margin_bottom: int = 30
         self._line_color = QColor("#5B9DF5")
         self._grid_color = QColor("#2A3441")
         self._text_color = QColor("#CBD5E1")
 
     # ── Qt properties ─────────────────────────────────────────────────────
 
-    @Property("QVariantList", notify=dataChanged)
-    def data(self) -> list[float]:
-        return self._data
-
-    @data.setter  # type: ignore[no-redef]
-    def data(self, val) -> None:
-        coerced = self._coerce_floats(val)
-        if coerced == self._data:
-            return
-        self._data = coerced
-        self.dataChanged.emit()
-        self.hasDataChanged.emit()
-        self.update()
-
     @Property(bool, notify=hasDataChanged)
     def hasData(self) -> bool:
-        """True when the data list has at least one point.
+        """True when at least one point is buffered.
 
-        QML can bind to this safely (QVariantList `.length` is not bindable).
+        QML can bind to this safely (a plain list length is not bindable).
         """
-        return len(self._data) > 0
+        return len(self._points) > 0
 
     @Property(QColor, notify=lineColorChanged)
     def lineColor(self) -> QColor:
@@ -129,24 +121,48 @@ class TrendChartItem(QQuickPaintedItem):
         self.paddingChanged.emit()
         self.update()
 
-    # ── Convenience slot for QML: accept a JSON string from a Signal(str) ──
+    # ── slots for QML: streamController.trendDelta / trendReset ────────────
 
     @Slot(str)
-    def setDataFromJson(self, avgs_json: str) -> None:
+    def appendDelta(self, delta_json: str) -> None:
-        """Slot for QML Connections handler: parse JSON array and update data.
+        """Append new (elapsed_s, value) points and prune the 60s window.
 
-        Mirrors `streamController.trendData` (which emits JSON-encoded floats).
+        Mirrors `streamController.trendDelta`, which emits one new pair per
+        live frame as `[[elapsed_s, value], ...]`.
         """
         try:
-            parsed = json.loads(avgs_json) if avgs_json else []
+            parsed = json.loads(delta_json) if delta_json else []
         except (json.JSONDecodeError, TypeError) as exc:
-            log.error("TrendChartItem: failed to parse trend JSON: %s", exc)
+            log.error("TrendChartItem: failed to parse trend delta JSON: %s", exc)
             return
-        coerced = self._coerce_floats(parsed)
+
-        if coerced == self._data:
+        had_data = len(self._points) > 0
+        added = False
+        for pair in parsed:
+            try:
+                elapsed, value = float(pair[0]), float(pair[1])
+            except (TypeError, ValueError, IndexError):
+                continue
+            self._points.append((elapsed, value))
+            added = True
+
+        if not added:
             return
-        self._data = coerced
+
-        self.dataChanged.emit()
+        latest_elapsed = self._points[-1][0]
+        cutoff = latest_elapsed - WINDOW_SECONDS
+        self._points = [p for p in self._points if p[0] >= cutoff]
+
+        if not had_data:
+            self.hasDataChanged.emit()
+        self.update()
+
+    @Slot()
+    def clearTrend(self) -> None:
+        """Clear all buffered points (new stream started)."""
+        if not self._points:
+            return
+        self._points = []
         self.hasDataChanged.emit()
         self.update()
 
@@ -169,51 +185,30 @@ class TrendChartItem(QQuickPaintedItem):
 
         self._draw_grid(painter, plot_rect)
 
-        if len(self._data) < 2:
+        if len(self._points) < 2:
             return
 
-        y_min, y_max = self._y_range()
+        window_end = self._points[-1][0]
-        self._draw_axes_labels(painter, plot_rect, y_min, y_max)
+        window_start = max(0.0, window_end - WINDOW_SECONDS)
-        self._draw_line(painter, plot_rect, y_min, y_max)
+        self._draw_axes_labels(painter, plot_rect, window_start, window_end)
+        self._draw_line(painter, plot_rect, window_start, window_end)
 
     # ── internals ─────────────────────────────────────────────────────────
 
-    def _coerce_floats(self, val) -> list[float]:
+    def _x_to_px(self, elapsed: float, window_start: float, window_end: float, plot_rect: QRectF) -> float:
-        if not val:
+        return elapsed_to_pixel(elapsed, window_start, window_end, plot_rect.left(), plot_rect.width())
-            return []
-        out: list[float] = []
-        for v in val:
-            try:
-                out.append(float(v))
-            except (TypeError, ValueError):
-                continue
-        return out
 
-    def _y_range(self) -> tuple[float, float]:
+    def _y_to_px(self, value: float, plot_rect: QRectF) -> float:
-        lo = min(self._data)
+        px = value_to_pixel(value, Y_MIN, Y_MAX, plot_rect.top(), plot_rect.height())
-        hi = max(self._data)
+        # Clamp: a sensor reading outside 0-200°C shouldn't paint outside the widget.
-        if hi - lo < 1e-9:
+        return max(plot_rect.top(), min(plot_rect.bottom(), px))
-            lo, hi = lo - 5.0, hi + 5.0
-        # Snap to a "nice" tick step (1/2/5 × 10^k) so the axis holds still
-        # while streaming and only moves when data crosses a step boundary —
-        # raw min/max rescaled every frame, which read as an unstable chart.
-        raw_step = (hi - lo) / 4
-        mag = 10 ** math.floor(math.log10(raw_step))
-        step = next(s * mag for s in (1, 2, 5, 10) if s * mag >= raw_step)
-        return math.floor(lo / step) * step, math.ceil(hi / step) * step
-
-    def _x_to_px(self, i: int, n: int, plot_rect: QRectF) -> float:
-        return index_to_pixel(i, n, plot_rect.left(), plot_rect.width())
-
-    def _y_to_px(self, v: float, y_min: float, y_max: float, plot_rect: QRectF) -> float:
-        return value_to_pixel(v, y_min, y_max, plot_rect.top(), plot_rect.height())
 
     def _draw_grid(self, painter: QPainter, plot_rect: QRectF) -> None:
         pen = QPen(self._grid_color)
         pen.setWidthF(1.0)
         pen.setCosmetic(True)
         painter.setPen(pen)
-        rows = 4
+        rows = len(Y_TICKS) - 1
         for i in range(rows + 1):
             y = plot_rect.top() + (i / rows) * plot_rect.height()
             painter.drawLine(int(plot_rect.left()), int(y),
@@ -223,36 +218,29 @@ class TrendChartItem(QQuickPaintedItem):
         self,
         painter: QPainter,
         plot_rect: QRectF,
-        y_min: float,
+        window_start: float,
-        y_max: float,
+        window_end: float,
     ) -> None:
         painter.setPen(self._text_color)
         font = QFont(painter.font())
         font.setPointSizeF(max(7.0, font.pointSizeF() * 0.85))
         painter.setFont(font)
 
-        rows = 4
+        title_w = 14  # leftmost sliver reserved for the rotated "Temp" title
-        label_w = self._margin_left - 4  # 4px gutter before the plot area
+        label_w = self._margin_left - 4 - title_w  # 4px gutter before the plot area
-        for i in range(rows + 1):
+        for tick in reversed(Y_TICKS):
-            t = i / rows
+            y_px = self._y_to_px(tick, plot_rect)
-            y_val = y_max - t * (y_max - y_min)
+            painter.drawText(QRectF(title_w, y_px - 7, label_w, 14),
-            y_px = plot_rect.top() + t * plot_rect.height()
-            label = f"{y_val:g}"
-            painter.drawText(QRectF(0, y_px - 7, label_w, 14),
                              Qt.AlignmentFlag.AlignRight | Qt.AlignmentFlag.AlignVCenter,
-                             label)
+                             str(tick))
 
-        # X-axis: sample index. `trendData` carries plain averages with no
+        # X-axis: elapsed seconds within the current rolling window.
-        # timestamps attached, so index is the only x-coordinate available —
+        cols = 4
-        # it reads correctly for review mode (index == frame number) and as a
-        # relative recency order for the live rolling window. paint() already
-        # guarantees len(self._data) >= 2 before calling this.
-        n = len(self._data)
-        cols = min(4, n - 1)
         y_px = plot_rect.bottom() + 4
         for i in range(cols + 1):
-            idx = round((i / cols) * (n - 1))
+            t_val = window_start + (i / cols) * (window_end - window_start)
-            x_px = self._x_to_px(idx, n, plot_rect)
+            x_px = self._x_to_px(t_val, window_start, window_end, plot_rect)
+            label = f"{t_val:.0f}"
             if i == 0:
                 rect = QRectF(x_px, y_px, 40, 14)
                 align = Qt.AlignmentFlag.AlignLeft
@@ -263,16 +251,36 @@ class TrendChartItem(QQuickPaintedItem):
             else:
                 rect = QRectF(x_px - 20, y_px, 40, 14)
                 align = Qt.AlignmentFlag.AlignHCenter
-            painter.drawText(rect, align | Qt.AlignmentFlag.AlignTop, str(idx))
+            painter.drawText(rect, align | Qt.AlignmentFlag.AlignTop, label)
+
+        self._draw_axis_titles(painter, plot_rect, title_w, y_px + 18)
+
+    def _draw_axis_titles(
+        self,
+        painter: QPainter,
+        plot_rect: QRectF,
+        title_w: float,
+        x_label_bottom: float,
+    ) -> None:
+        # Y axis: "Temp", rotated upright, centered along the plot's height.
+        painter.save()
+        painter.translate(title_w / 2, plot_rect.center().y())
+        painter.rotate(-90)
+        painter.drawText(QRectF(-plot_rect.height() / 2, -7, plot_rect.height(), 14),
+                         Qt.AlignmentFlag.AlignCenter, "Temp (°C)")
+        painter.restore()
+
+        # X axis: "Time", centered under the elapsed-seconds tick row.
+        painter.drawText(QRectF(plot_rect.left(), x_label_bottom, plot_rect.width(), 14),
+                         Qt.AlignmentFlag.AlignHCenter | Qt.AlignmentFlag.AlignTop, "Time")
 
     def _draw_line(
         self,
         painter: QPainter,
         plot_rect: QRectF,
-        y_min: float,
+        window_start: float,
-        y_max: float,
+        window_end: float,
     ) -> None:
-        n = len(self._data)
         pen = QPen(self._line_color)
         pen.setWidthF(2.0)
         pen.setCosmetic(True)
@@ -281,15 +289,16 @@ class TrendChartItem(QQuickPaintedItem):
         painter.setPen(pen)
 
         poly = QPolygon()
-        for i, v in enumerate(self._data):
+        for elapsed, value in self._points:
-            px = self._x_to_px(i, n, plot_rect)
+            px = self._x_to_px(elapsed, window_start, window_end, plot_rect)
-            py = self._y_to_px(v, y_min, y_max, plot_rect)
+            py = self._y_to_px(value, plot_rect)
             poly.append(QPoint(int(px), int(py)))
         painter.drawPolyline(poly)
 
         # Trailing dot at the last data point
-        last_x = int(self._x_to_px(n - 1, n, plot_rect))
+        last_elapsed, last_value = self._points[-1]
-        last_y = int(self._y_to_px(self._data[-1], y_min, y_max, plot_rect))
+        last_x = int(self._x_to_px(last_elapsed, window_start, window_end, plot_rect))
+        last_y = int(self._y_to_px(last_value, plot_rect))
         painter.setBrush(self._line_color)
         painter.setPen(Qt.PenStyle.NoPen)
         radius = 3

src/pygui/backend/visualization/wafer_map_item.py

@@ -14,7 +14,7 @@ import logging
 import math
 
 import numpy as np
-from PySide6.QtCore import Property, QPoint, Qt, Signal, Slot
+from PySide6.QtCore import Property, QPoint, QRectF, Qt, Signal, Slot
 from PySide6.QtGui import (
     QBrush,
     QColor,
@@ -310,17 +310,42 @@ class WaferMapItem(QQuickPaintedItem):
         Returns:
         True on success, False on failure
         """
-        if not file_path:
+        if not file_path or not self._values:
+            # No file loaded / no stream played yet — only the empty template
+            # would render, which isn't a meaningful export.
             return False
         try:
-            result = self.grabToImage()
+            # Render synchronously via paint() into our own image —
-            img = result.image()  # type: ignore[attr-defined]
+            # grabToImage() resolves on a later render frame, so its result
-            img.save(file_path, "PNG")
+            # is null when read immediately (the old silent failure).
-            return True
+            w, h = int(self.width()), int(self.height())
+            if w <= 0 or h <= 0:
+                return False
+            metrics = self._metrics_text()
+            footer_h = 28 if metrics else 0
+            img = QImage(w, h + footer_h, QImage.Format.Format_ARGB32)
+            img.fill(0)  # transparent background
+            painter = QPainter(img)
+            self.paint(painter)
+            if metrics:
+                footer = QRectF(0, h, w, footer_h)
+                painter.fillRect(footer, QColor("#101014"))
+                painter.setPen(QColor("#CBD5E1"))
+                painter.drawText(footer, Qt.AlignmentFlag.AlignCenter, metrics)
+            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 _rebuild_thickness(self) -> None:

tests/test_chart_geometry.py

@@ -1,6 +1,10 @@
 import pytest
 
-from pygui.backend.visualization.chart_geometry import index_to_pixel, value_to_pixel
+from pygui.backend.visualization.chart_geometry import (
+    elapsed_to_pixel,
+    index_to_pixel,
+    value_to_pixel,
+)
 
 
 def test_value_to_pixel_min_maps_to_bottom():
@@ -26,3 +30,23 @@ def test_index_to_pixel_first_and_last():
 
 def test_index_to_pixel_single_point_centers():
     assert index_to_pixel(0, 1, pixel_start=0.0, pixel_span=100.0) == pytest.approx(50.0)
+
+
+def test_elapsed_to_pixel_window_start_maps_to_left():
+    assert elapsed_to_pixel(10.0, window_start=10.0, window_end=70.0,
+                             pixel_start=0.0, pixel_span=200.0) == pytest.approx(0.0)
+
+
+def test_elapsed_to_pixel_window_end_maps_to_right():
+    assert elapsed_to_pixel(70.0, window_start=10.0, window_end=70.0,
+                             pixel_start=0.0, pixel_span=200.0) == pytest.approx(200.0)
+
+
+def test_elapsed_to_pixel_midpoint():
+    assert elapsed_to_pixel(40.0, window_start=10.0, window_end=70.0,
+                             pixel_start=0.0, pixel_span=200.0) == pytest.approx(100.0)
+
+
+def test_elapsed_to_pixel_degenerate_window_pins_right():
+    assert elapsed_to_pixel(5.0, window_start=5.0, window_end=5.0,
+                             pixel_start=0.0, pixel_span=200.0) == pytest.approx(200.0)

tests/test_device_controller.py

@@ -233,3 +233,12 @@ def test_device_service_port_caching(controller):
         service.enumerate_ports()
         assert mock_run.call_count == 2
 
+
+
+def test_export_dir_created_under_save_data_dir(controller):
+    from pathlib import Path
+
+    result = controller.exportDir()
+
+    assert result == str(Path(controller.saveDataDir) / "Export")
+    assert Path(result).is_dir()

tests/test_session_controller.py

@@ -1,8 +1,11 @@
+import json
 from unittest.mock import MagicMock
 
 import pytest
 
+import pygui.backend.controllers.session_controller as session_controller_module
 from pygui.backend.controllers.session_controller import SessionController
+from pygui.backend.models.frame import Frame
 
 
 @pytest.fixture
@@ -194,3 +197,31 @@ def test_export_segment_bad_index(qapp, controller, tmp_path):
     controller.segmentExported.connect(exported)
     controller.exportSegment(99)
     assert exported.call_args[0][0]["success"] is False
+
+
+def test_reset_live_trend_sets_start_time_and_emits_reset(controller, monkeypatch):
+    monkeypatch.setattr(session_controller_module.time, "monotonic", lambda: 100.0)
+
+    reset_seen = MagicMock()
+    controller.trendReset.connect(reset_seen)
+    controller._reset_live_trend()
+
+    assert controller._stream_start_time == 100.0
+    assert reset_seen.called
+
+
+def test_on_live_frame_emits_trend_delta_with_elapsed_seconds(controller, monkeypatch):
+    controller._stream_start_time = 100.0
+    monkeypatch.setattr(session_controller_module.time, "monotonic", lambda: 102.5)
+
+    delta_seen = MagicMock()
+    controller.trendDelta.connect(delta_seen)
+
+    frame = Frame(seq=1, time=102.5, values=[10.0, 20.0, 30.0])
+    controller._on_live_frame(frame)
+
+    payload = json.loads(delta_seen.call_args[0][0])
+    assert len(payload) == 1
+    elapsed, avg = payload[0]
+    assert elapsed == pytest.approx(2.5)
+    assert avg == pytest.approx(20.0)

tests/test_trend_chart_item.py

@@ -0,0 +1,82 @@
+"""Tests for src/pygui/backend/visualization/trend_chart_item.py."""
+import json
+
+import pytest
+
+# Use the session-scoped qapp fixture from conftest.py so Qt Property/Signal
+# descriptors work properly.
+pytestmark = pytest.mark.usefixtures("qapp")
+
+
+def test_no_data_initially():
+    from pygui.backend.visualization.trend_chart_item import TrendChartItem
+
+    item = TrendChartItem()
+    assert item.hasData is False
+
+
+def test_append_delta_adds_point_and_sets_has_data():
+    from pygui.backend.visualization.trend_chart_item import TrendChartItem
+
+    item = TrendChartItem()
+    item.appendDelta(json.dumps([[1.5, 42.0]]))
+
+    assert item.hasData is True
+    assert item._points == [(1.5, 42.0)]
+
+
+def test_append_delta_accumulates_across_calls():
+    from pygui.backend.visualization.trend_chart_item import TrendChartItem
+
+    item = TrendChartItem()
+    item.appendDelta(json.dumps([[0.0, 10.0]]))
+    item.appendDelta(json.dumps([[1.0, 20.0]]))
+
+    assert item._points == [(0.0, 10.0), (1.0, 20.0)]
+
+
+def test_append_delta_prunes_points_older_than_60s_window():
+    from pygui.backend.visualization.trend_chart_item import TrendChartItem
+
+    item = TrendChartItem()
+    item.appendDelta(json.dumps([[0.0, 10.0]]))
+    item.appendDelta(json.dumps([[70.0, 20.0]]))
+
+    assert item._points == [(70.0, 20.0)]
+
+
+def test_append_delta_ignores_malformed_json():
+    from pygui.backend.visualization.trend_chart_item import TrendChartItem
+
+    item = TrendChartItem()
+    item.appendDelta("not json")
+
+    assert item._points == []
+    assert item.hasData is False
+
+
+def test_append_delta_skips_repaint_when_no_points_added():
+    from unittest.mock import MagicMock
+
+    from pygui.backend.visualization.trend_chart_item import TrendChartItem
+
+    item = TrendChartItem()
+    item.appendDelta(json.dumps([[1.0, 10.0]]))
+    item.update = MagicMock()
+
+    item.appendDelta("not json")
+
+    assert item.update.called is False
+
+
+def test_clear_trend_resets_points_and_has_data():
+    from pygui.backend.visualization.trend_chart_item import TrendChartItem
+
+    item = TrendChartItem()
+    item.appendDelta(json.dumps([[1.0, 10.0]]))
+    assert item.hasData is True
+
+    item.clearTrend()
+
+    assert item._points == []
+    assert item.hasData is False

tests/test_wafer_map_item.py

@@ -8,20 +8,6 @@ import pytest
 pytestmark = pytest.mark.usefixtures("qapp")
 
 
-def test_export_image_valid_path():
-    """export_image saves a PNG when grabToImage succeeds."""
-    from pygui.backend.visualization.wafer_map_item import WaferMapItem
-
-    item = WaferMapItem()
-
-    mock_image = MagicMock()
-    mock_result = MagicMock()
-    mock_result.image.return_value = mock_image
-    item.grabToImage = MagicMock(return_value=mock_result)
-
-    assert item.export_image("/tmp/test_wafer.png") is True
-
-
 def test_export_image_empty_path():
     """export_image returns False for empty/None path."""
     from pygui.backend.visualization.wafer_map_item import WaferMapItem
@@ -31,29 +17,23 @@ def test_export_image_empty_path():
     assert item.export_image(None) is False
 
 
-def test_export_image_grab_fails():
+def test_export_image_zero_size_item_fails():
-    """export_image returns False when grabToImage raises."""
+    """export_image returns False when the item has no geometry to render."""
     from pygui.backend.visualization.wafer_map_item import WaferMapItem
 
     item = WaferMapItem()
-    item.grabToImage = MagicMock(side_effect=RuntimeError("grab failed"))
-
     assert item.export_image("/tmp/test_wafer.png") is False
 
 
-def test_export_image_save_fails():
+def test_export_image_unwritable_path_fails(tmp_path):
-    """export_image returns False when image.save raises."""
+    """export_image returns False when the target directory doesn't exist."""
     from pygui.backend.visualization.wafer_map_item import WaferMapItem
 
-    mock_image = MagicMock()
-    mock_image.save.side_effect = IOError("disk full")
-    mock_result = MagicMock()
-    mock_result.image.return_value = mock_image
-
     item = WaferMapItem()
-    item.grabToImage = MagicMock(return_value=mock_result)
+    item.setWidth(100)
-
+    item.setHeight(100)
-    assert item.export_image("/tmp/test_wafer.png") is False
+    item.values = [10.0, 20.0, 30.0]
+    assert item.export_image(str(tmp_path / "no_such_dir" / "wafer.png")) is False
 
 
 def test_thickness_properties():
@@ -88,3 +68,57 @@ def test_show_thickness_setter():
 
     item.showThickness = True
     assert item._show_thickness is True
+
+
+def test_export_image_writes_real_png_headless(tmp_path):
+    """export_image must produce an actual decodable image file without a
+    QQuickWindow — the button was silently failing because grabToImage()
+    resolves asynchronously and never completes headless/immediately."""
+    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]
+    out = tmp_path / "wafer.png"
+
+    assert item.export_image(str(out)) is True
+    assert out.exists()
+    loaded = QImage(str(out))
+    assert not loaded.isNull()
+    assert loaded.width() == 200
+
+
+def test_export_image_includes_metrics_footer(tmp_path):
+    """With sensor values loaded, the export gains a footer strip below the
+    map carrying the metric readouts (sensors / min / max / avg)."""
+    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]
+    out = tmp_path / "wafer.png"
+
+    assert item.export_image(str(out)) is True
+    loaded = QImage(str(out))
+    assert loaded.height() > 200  # footer strip appended
+    # footer is painted opaque (dark bg), not transparent
+    assert loaded.pixelColor(5, loaded.height() - 5).alpha() == 255
+
+
+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
+
+    item = WaferMapItem()
+    item.setWidth(200)
+    item.setHeight(200)
+    out = tmp_path / "wafer.png"
+
+    assert item.export_image(str(out)) is False
+    assert not out.exists()