fix(desktop): apply saved units to new and BOM-created nests

New only fell back to the legacy DefaultUnit setting when the whole
defaults file was missing or invalid, so a readable file without a
usable unit produced inches. BOM import never assigned units at all,
and the Nest Defaults dialog showed inches for a missing file.

All three now load through MainForm.LoadSavedNestDefaults, which passes
DefaultUnit as the per-field unit fallback. BOM-created nests start from
NestDefaults.ApplyTo, like New, before applying each group's plate size
and spacing.

The ApplyTo test now asserts units; removing the unit assignment from
ApplyTo fails it. WinForms behaviour is compile-verified only on Linux.

OpenNest.Tests/Data/NestDefaultsTests.cs

@@ -261,7 +261,7 @@ public class NestDefaultsTests : IDisposable
     [Fact]
     public void ApplyTo_SetsUnitsAndPlateDefaults_AndDoesNotAliasSourceNest()
     {
-        var source = new Nest();
+        var source = new Nest { Units = Units.Millimeters };
         source.PlateDefaults.Size = new Size(48, 96);
         source.PlateDefaults.EdgeSpacing = new Spacing(1.25, 1.25, 1.25, 1.25);
         var defaults = NestDefaults.FromNest(source);
@@ -273,6 +273,8 @@ public class NestDefaultsTests : IDisposable
         var target = new Nest();
         defaults.ApplyTo(target);
 
+        // New and BOM-created nests both take their units from ApplyTo.
+        Assert.Equal(Units.Millimeters, target.Units);
         Assert.Equal(new Size(48, 96), target.PlateDefaults.Size);
         Assert.Equal(
             new Spacing(1.25, 1.25, 1.25, 1.25),

OpenNest/Forms/BomImportForm.cs

@@ -26,7 +26,7 @@ namespace OpenNest.Forms
             InitializeComponent();
             _parts = new List<BomPartRow>();
             _groupSettings = new Dictionary<string, GroupSettings>();
-            _defaults = NestDefaults.Load(NestDefaults.DefaultPath);
+            _defaults = MainForm.LoadSavedNestDefaults(out _);
             ApplyDefaults();
         }
 
@@ -465,10 +465,12 @@ namespace OpenNest.Forms
                 var nest = new Nest(nestName);
                 nest.DateCreated = DateTime.Now;
                 nest.DateLastModified = DateTime.Now;
+                // Saved defaults first (units, quadrant, plate), as New does;
+                // then the group's own plate size and spacing.
+                _defaults.ApplyTo(nest);
                 nest.PlateDefaults.Size = new Geometry.Size(plateWidth, plateLength);
                 nest.Thickness = thickness;
                 nest.Material = new Material(material);
-                nest.PlateDefaults.Quadrant = _defaults.Quadrant;
                 nest.PlateDefaults.PartSpacing = partSpacing;
                 nest.PlateDefaults.EdgeSpacing = new Spacing(
                     edgeLeft,

OpenNest/Forms/MainForm.cs

@@ -108,17 +108,12 @@ namespace OpenNest.Forms
         }
 
         /// <summary>
-        /// Loads the persisted nest defaults. When no usable file exists,
-        /// units come from the legacy DefaultUnit setting; a corrupt file
-        /// warns once per session.
+        /// Loads the persisted nest defaults (see <see cref="LoadSavedNestDefaults"/>);
+        /// a corrupt or unreadable file warns once per session.
         /// </summary>
         private NestDefaults LoadNestDefaults()
         {
-            var defaults = NestDefaults.Load(NestDefaults.DefaultPath, out var status);
-            if (status == NestDefaultsStatus.Ok)
-                return defaults;
-
-            defaults.Units = Properties.Settings.Default.DefaultUnit;
+            var defaults = LoadSavedNestDefaults(out var status);
 
             if (status == NestDefaultsStatus.Invalid && !defaultsWarned)
             {
@@ -135,6 +130,19 @@ namespace OpenNest.Forms
 
         private bool defaultsWarned;
 
+        /// <summary>
+        /// The single desktop entry point for persisted nest defaults. Units
+        /// fall back to the legacy DefaultUnit setting whenever the file is
+        /// missing or unusable or has no valid unit, so New, BOM import and
+        /// the defaults dialog always agree.
+        /// </summary>
+        internal static NestDefaults LoadSavedNestDefaults(out NestDefaultsStatus status) =>
+            NestDefaults.Load(
+                NestDefaults.DefaultPath,
+                Properties.Settings.Default.DefaultUnit,
+                out status
+            );
+
         private string GetNestName(DateTime date, int id)
         {
             var year = (date.Year % 100).ToString("D2");
@@ -1155,7 +1163,7 @@ namespace OpenNest.Forms
 
         private void NestDefaults_Click(object sender, EventArgs e)
         {
-            using (var form = new NestDefaultsForm(NestDefaults.Load(NestDefaults.DefaultPath)))
+            using (var form = new NestDefaultsForm(LoadSavedNestDefaults(out _)))
             {
                 if (form.ShowDialog(this) == DialogResult.OK)
                     form.GetDefaults().Save(NestDefaults.DefaultPath);