always show the Path A angle and default it from the geometry

src/main/java/org/micromanager/lightsheetmanager/api/data/GeometryType.java

@@ -3,24 +3,39 @@
 import java.util.Arrays;
 
 public enum GeometryType {
-    UNKNOWN("Unknown"),
-    DISPIM("diSPIM"),
-    ISPIM("iSPIM"),
-    OSPIM("oSPIM"),
-    MESOSPIM("mesoSPIM"),
-    SCAPE("SCAPE");
+    UNKNOWN("Unknown", 45.0),
+    DISPIM("diSPIM", 45.0),
+    ISPIM("iSPIM", 45.0),
+    OSPIM("oSPIM", 60.0),
+    MESOSPIM("mesoSPIM", 45.0),
+    SCAPE("SCAPE", 50.0);
 
     private final String label_;
+    private final double firstViewAngle_;
 
-    GeometryType(final String label) {
+    GeometryType(final String label, final double firstViewAngle) {
         label_ = label;
+        firstViewAngle_ = firstViewAngle;
     }
 
     @Override
     public String toString() {
         return label_;
     }
 
+    /**
+     * Returns the nominal angle in degrees between the objective and the stage.
+     *
+     * <p>Each geometry is built to a different angle, so this is only a starting point
+     * for a new install. Every build is aligned by hand, and the angle a user measures
+     * on their own microscope is the one that belongs in the settings.
+     *
+     * @return the angle in degrees
+     */
+    public double defaultFirstViewAngle() {
+        return firstViewAngle_;
+    }
+
     public static GeometryType fromString(final String propertyValue) {
         if (propertyValue == null || propertyValue.isEmpty()) {
             return UNKNOWN;

src/main/java/org/micromanager/lightsheetmanager/gui/tabs/SettingsTab.java

@@ -93,7 +93,7 @@ private void createUserInterface() {
 
         spnScanFirstViewAngle_ = Spinner.createDoubleSpinner(
                 settings.stageScan().firstViewAngle(),
-                1.0, 89.0, 1.0);
+                1.0, 89.0, 0.1);
 
         // Scan CheckBoxes
         cbxScanFromCurrentPosition_ = new CheckBox("Scan from current position instead of center",
@@ -133,13 +133,20 @@ private void createUserInterface() {
             pnlScanSettings.add(spnScanOvershootDist_, "wrap");
             pnlScanSettings.add(lblScanRetraceSpeed, "");
             pnlScanSettings.add(spnScanRetraceSpeed_, "wrap");
-            pnlScanSettings.add(lblScanAngleFirstView, "");
-            pnlScanSettings.add(spnScanFirstViewAngle_, "wrap");
+        }
+
+        // the grid slice step size is derived from the angle as well, so it stays
+        // available even when the stage cannot scan
+        pnlScanSettings.add(lblScanAngleFirstView, "");
+        pnlScanSettings.add(spnScanFirstViewAngle_, "wrap");
+
+        if (isUsingScanSettings_) {
             pnlScanSettings.add(cbxScanFromCurrentPosition_, "span 2, wrap");
             pnlScanSettings.add(cbxScanNegativeDirection_, "span 2, wrap");
             pnlScanSettings.add(cbxReturnToStart_, "span 2, wrap");
         } else {
-            pnlScanSettings.add(new JLabel("Stage scanning not supported by your firmware."), "");
+            pnlScanSettings.add(new JLabel("Stage scanning not supported by your firmware."),
+                    "span 2");
         }
 
         // light sheet scanner settings panel
@@ -183,9 +190,6 @@ private void createEventHandlers() {
             spnScanRetraceSpeed_.registerListener(
                     () -> model_.acquisitions().settingsBuilder().stageScanBuilder()
                             .retraceSpeed(spnScanRetraceSpeed_.getDouble()));
-            spnScanFirstViewAngle_.registerListener(
-                    () -> model_.acquisitions().settingsBuilder().stageScanBuilder()
-                            .firstViewAngle(spnScanFirstViewAngle_.getDouble()));
 
             cbxScanFromCurrentPosition_.registerListener(
                     () -> model_.acquisitions().settingsBuilder().stageScanBuilder()
@@ -198,6 +202,11 @@ private void createEventHandlers() {
                             .returnToStart(cbxReturnToStart_.isSelected()));
         }
 
+        // registered outside the block above because the angle spinner is always shown
+        spnScanFirstViewAngle_.registerListener(
+                () -> model_.acquisitions().settingsBuilder().stageScanBuilder()
+                        .firstViewAngle(spnScanFirstViewAngle_.getDouble()));
+
         // ASIScanner Filter Freq
         if (isUsingPLogic_) {
             final ASIScanner scanner = model_.devices().device("IllumSlice");

src/main/java/org/micromanager/lightsheetmanager/model/acquisitions/AcquisitionEngine.java

@@ -65,10 +65,7 @@ public abstract class AcquisitionEngine implements AcquisitionManager, MMAcquist
      * Validates that the acquisition can actually be written to disk, before anything is acquired.
      * <p>
      * The images are written by {@code finish()}, i.e. only AFTER the run completes, so without this
-     * check an unusable save location is discovered at the very end and the data is lost. Observed
-     * 2026-07-27: a 41 s dual-camera run ended in "could not save the acquisition data to:
-     * D:\SCOPE\test\Test" because {@code D:\SCOPE\test} did not exist. The same path also silently
-     * drops {@code acq_settings.json} and {@code position_list.pos}, which are written up front.
+     * check an unusable save location is discovered at the very end and the data is lost.
      * <p>
      * Called from both geometry engines' {@code setup()} before any hardware is touched, so a failure
      * costs nothing and leaves the microscope untouched.
@@ -125,8 +122,6 @@ protected boolean validateSaveLocation() {
      * <p>Cameras that disagree overrun the shared Core circular buffer and take the whole JVM with
      * them: {@code EXCEPTION_ACCESS_VIOLATION} inside {@code popNextImageMD}, no Java exception, no
      * recovery, no data. Refusing to arm is the only place this can be stopped from inside LSM.
-     * Observed in the field 2026-07-28 on a dual-Kinetix rig where a partly-applied ROI left one
-     * camera at 1200x1200 and the other at 600x600.
      *
      * <p>Called from both geometry engines' {@code setup()} before any hardware is touched, so a
      * failure costs nothing and leaves the microscope untouched.
@@ -223,6 +218,10 @@ public AcquisitionEngine(final LightSheetManager model) {
 
         // default settings
         asb_ = ScapeAcquisitionSettings.builder();
+        // seeded from the geometry because the angle has no single sensible default;
+        // a saved profile replaces it later when UserSettings loads
+        asb_.stageScanBuilder().firstViewAngle(
+                model.devices().adapter().geometry().defaultFirstViewAngle());
         acqSettings_ = asb_.build();
     }