feat: live energy/wavelength readout in Beamline setup

New 'Current energy / lambda' row above the setpoint, fed per DAQ
tick from diffraction.energy_keV; the setpoint row is renamed
'Set Energy (keV)' so 'what is' and 'what to set' are distinct.
Guards energy 0.0 (server's detector-unavailable fallback) because
the wavelength property divides by it. The copied energy row in the
experiment configuration is renamed to match.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/aare/gui/panels/data_collection_settings.py

@@ -97,7 +97,7 @@ class DataCollectionSettings(QFrame):
         energy_row = QWidget(self)
         energy_layout = QHBoxLayout(energy_row)
         energy_layout.setContentsMargins(0, 0, 0, 0)
-        energy_layout.addWidget(QLabel("Energy (keV)", parent=energy_row))
+        energy_layout.addWidget(QLabel("Set Energy (keV)", parent=energy_row))
         energy_layout.addWidget(self.energy_spin)
         energy_layout.addWidget(self.change_energy_button)
 

src/aare/gui/panels/monochromator_panel.py

@@ -26,22 +26,28 @@ class MonochromatorPanel(QWidget):
         self.mono_pitch_scan_button.clicked.connect(self.mono_pitch_scan.emit)
         grid_layout.addWidget(self.mono_pitch_scan_button, 1, 0, 1, 3)
 
+        # Live readout above the setpoint, so "what is" and "what to set"
+        # stop sharing one ambiguous Energy row. Fed per DAQ tick.
+        grid_layout.addWidget(QLabel("Current energy / λ", parent=self), 2, 0)
+        self.current_energy_label = QLabel("—", parent=self)
+        grid_layout.addWidget(self.current_energy_label, 2, 1, 1, 2)
+
         # One row (label | value | button) instead of three — vertical space.
         # Display in keV; the DAQ API stays in eV (converted on emit).
         # Unit lives in the label, not as a spinbox suffix — the suffix ate
         # field width and sat between the value and the +/- arrow.
-        grid_layout.addWidget(QLabel("Energy (keV)", parent=self), 2, 0)
+        grid_layout.addWidget(QLabel("Set Energy (keV)", parent=self), 3, 0)
 
         self.energy_spin = QDoubleSpinBox(parent=self)
         self.energy_spin.setDecimals(3)
         self.energy_spin.setRange(1.0, 30.0)
         self.energy_spin.setSingleStep(0.1)
         self.energy_spin.setValue(12.0)
-        grid_layout.addWidget(self.energy_spin, 2, 1)
+        grid_layout.addWidget(self.energy_spin, 3, 1)
 
         self.change_energy_button = QPushButton("Change Energy", parent=self)
         self.change_energy_button.clicked.connect(self._emit_change_energy)
-        grid_layout.addWidget(self.change_energy_button, 2, 2)
+        grid_layout.addWidget(self.change_energy_button, 3, 2)
 
         # TODO(wire backend): no DAQ endpoint exists yet for moving the beam
         # to the box center — shown disabled as WIP until the operation is
@@ -51,12 +57,21 @@ class MonochromatorPanel(QWidget):
         self.move_beam_to_box_button.setToolTip("Coming soon — not functional yet.")
         self.move_beam_to_box_button.setEnabled(False)
         self.move_beam_to_box_button.clicked.connect(self.move_beam_to_box.emit)
-        grid_layout.addWidget(self.move_beam_to_box_button, 3, 0, 1, 3)
+        grid_layout.addWidget(self.move_beam_to_box_button, 4, 0, 1, 3)
 
     @Slot()
     def _emit_change_energy(self):
         self.change_energy.emit(float(self.energy_spin.value()) * 1000.0)
 
     @Slot(DAQStatusModel)
-    def update_daq_status(self, _status: DAQStatusModel):
-        pass
+    def update_daq_status(self, status: DAQStatusModel):
+        energy = status.diffraction.energy_keV
+        # 0.0 is the server's detector-unavailable fallback, and the
+        # wavelength property divides by it — guard before touching it.
+        if not energy:
+            text = "— / —"
+        else:
+            text = f"{energy:.3f} keV  /  {status.diffraction.wavelength_angstrom:.4f} Å"
+        # Guarded: runs per DAQ tick (2 Hz), skip the repaint when unchanged.
+        if self.current_energy_label.text() != text:
+            self.current_energy_label.setText(text)

tests/unit/gui/test_monochromator_panel.py

@@ -0,0 +1,16 @@
+from aare.gui.panels.monochromator_panel import MonochromatorPanel
+
+
+def test_current_energy_readout(qtbot, daq_status_factory):
+    panel = MonochromatorPanel()
+    qtbot.addWidget(panel)
+
+    status = daq_status_factory()
+    panel.update_daq_status(status)
+    assert panel.current_energy_label.text() == "12.000 keV  /  1.0332 Å"
+
+    # 0.0 is the server's detector-unavailable fallback; the wavelength
+    # property divides by energy, so the readout must not touch it.
+    status.diffraction = status.diffraction.model_copy(update={"energy_keV": 0.0})
+    panel.update_daq_status(status)
+    assert panel.current_energy_label.text() == "— / —"