feat: add PlateManager with navigation state and disposal

Introduces PlateChangedEventArgs and PlateManager in OpenNest.Core to centralize plate navigation logic (CurrentIndex, LoadFirst/Last/Next/Previous/At, IsFirst/IsLast). Includes full xUnit test coverage (17 tests) verifying navigation, event firing, and disposal unsubscription.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

OpenNest.Tests/PlateManagerTests.cs

@@ -0,0 +1,208 @@
+using OpenNest.CNC;
+using OpenNest.Geometry;
+
+namespace OpenNest.Tests;
+
+public class PlateManagerTests
+{
+    private static Nest CreateNest()
+    {
+        var nest = new Nest("test");
+        return nest;
+    }
+
+    private static Part MakePart()
+    {
+        var pgm = new Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(10, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(10, 10)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 0)));
+        var drawing = new Drawing("test", pgm);
+        return new Part(drawing);
+    }
+
+    [Fact]
+    public void Constructor_EmptyNest_CurrentIndexZero()
+    {
+        var nest = CreateNest();
+        using var mgr = new PlateManager(nest);
+        Assert.Equal(0, mgr.CurrentIndex);
+    }
+
+    [Fact]
+    public void Constructor_NestWithPlates_CurrentIndexZero()
+    {
+        var nest = CreateNest();
+        nest.CreatePlate();
+        nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        Assert.Equal(0, mgr.CurrentIndex);
+    }
+
+    [Fact]
+    public void CurrentPlate_ReturnsPlateAtCurrentIndex()
+    {
+        var nest = CreateNest();
+        var plate = nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        Assert.Same(plate, mgr.CurrentPlate);
+    }
+
+    [Fact]
+    public void CurrentPlate_EmptyNest_ReturnsNull()
+    {
+        var nest = CreateNest();
+        using var mgr = new PlateManager(nest);
+        Assert.Null(mgr.CurrentPlate);
+    }
+
+    [Fact]
+    public void Count_DelegatesToNestPlates()
+    {
+        var nest = CreateNest();
+        nest.CreatePlate();
+        nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        Assert.Equal(2, mgr.Count);
+    }
+
+    [Fact]
+    public void LoadFirst_SetsCurrentIndexToZero()
+    {
+        var nest = CreateNest();
+        nest.CreatePlate();
+        nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        mgr.LoadLast();
+        mgr.LoadFirst();
+        Assert.Equal(0, mgr.CurrentIndex);
+    }
+
+    [Fact]
+    public void LoadLast_SetsCurrentIndexToLastPlate()
+    {
+        var nest = CreateNest();
+        nest.CreatePlate();
+        nest.CreatePlate();
+        nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        mgr.LoadLast();
+        Assert.Equal(2, mgr.CurrentIndex);
+    }
+
+    [Fact]
+    public void LoadNext_AdvancesIndex()
+    {
+        var nest = CreateNest();
+        nest.CreatePlate();
+        nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        var result = mgr.LoadNext();
+        Assert.True(result);
+        Assert.Equal(1, mgr.CurrentIndex);
+    }
+
+    [Fact]
+    public void LoadNext_AtEnd_ReturnsFalse()
+    {
+        var nest = CreateNest();
+        nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        var result = mgr.LoadNext();
+        Assert.False(result);
+        Assert.Equal(0, mgr.CurrentIndex);
+    }
+
+    [Fact]
+    public void LoadPrevious_DecrementsIndex()
+    {
+        var nest = CreateNest();
+        nest.CreatePlate();
+        nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        mgr.LoadLast();
+        var result = mgr.LoadPrevious();
+        Assert.True(result);
+        Assert.Equal(0, mgr.CurrentIndex);
+    }
+
+    [Fact]
+    public void LoadPrevious_AtStart_ReturnsFalse()
+    {
+        var nest = CreateNest();
+        nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        var result = mgr.LoadPrevious();
+        Assert.False(result);
+        Assert.Equal(0, mgr.CurrentIndex);
+    }
+
+    [Fact]
+    public void LoadAt_SetsExactIndex()
+    {
+        var nest = CreateNest();
+        nest.CreatePlate();
+        nest.CreatePlate();
+        nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        mgr.LoadAt(2);
+        Assert.Equal(2, mgr.CurrentIndex);
+    }
+
+    [Fact]
+    public void IsFirst_WhenAtStart_ReturnsTrue()
+    {
+        var nest = CreateNest();
+        nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        Assert.True(mgr.IsFirst);
+    }
+
+    [Fact]
+    public void IsLast_WhenAtEnd_ReturnsTrue()
+    {
+        var nest = CreateNest();
+        nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        Assert.True(mgr.IsLast);
+    }
+
+    [Fact]
+    public void IsFirst_WhenNotAtStart_ReturnsFalse()
+    {
+        var nest = CreateNest();
+        nest.CreatePlate();
+        nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        mgr.LoadLast();
+        Assert.False(mgr.IsFirst);
+    }
+
+    [Fact]
+    public void Navigation_FiresCurrentPlateChanged()
+    {
+        var nest = CreateNest();
+        nest.CreatePlate();
+        nest.CreatePlate();
+        using var mgr = new PlateManager(nest);
+        PlateChangedEventArgs received = null;
+        mgr.CurrentPlateChanged += (s, e) => received = e;
+        mgr.LoadNext();
+        Assert.NotNull(received);
+        Assert.Equal(1, received.Index);
+        Assert.Same(nest.Plates[1], received.Plate);
+    }
+
+    [Fact]
+    public void Dispose_UnsubscribesFromPlateEvents()
+    {
+        var nest = CreateNest();
+        using var mgr = new PlateManager(nest);
+        var eventFired = false;
+        mgr.PlateListChanged += (s, e) => eventFired = true;
+        mgr.Dispose();
+        nest.CreatePlate();
+        Assert.False(eventFired);
+    }
+}