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.

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():
-    """export_image returns False when grabToImage raises."""
+def test_export_image_zero_size_item_fails():
+    """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():
-    """export_image returns False when image.save raises."""
+def test_export_image_unwritable_path_fails(tmp_path):
+    """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)
-
-    assert item.export_image("/tmp/test_wafer.png") is False
+    item.setWidth(100)
+    item.setHeight(100)
+    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()