feat(shapes): add PlateSizes catalog and wire Ctrl+P to snap-to-standard

PlateSizes holds standard mill sheet sizes (48x96 through 96x240) and
exposes Recommend() which snaps small layouts to an increment and
rounds larger layouts up to the nearest fitting sheet. Plate.SnapToStandardSize
applies the result while preserving long-axis orientation, and the
existing Ctrl+P "Resize to Fit" menu in EditNestForm now calls it
instead of the simple round-up AutoSize.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Core/Plate.cs

@@ -1,6 +1,7 @@
 using OpenNest.Collections;
 using OpenNest.Geometry;
 using OpenNest.Math;
+using OpenNest.Shapes;
 using System;
 using System.Collections.Generic;
 using System.Linq;
@@ -548,6 +549,65 @@ namespace OpenNest
                 Rounding.RoundUpToNearest(xExtent, roundingFactor));
         }
 
+        /// <summary>
+        /// Sizes the plate using the <see cref="PlateSizes"/> catalog: small
+        /// layouts snap to an increment, larger ones round up to the next
+        /// standard mill sheet. The plate's long-axis orientation (X vs Y)
+        /// is preserved. Does nothing if the plate has no parts.
+        /// </summary>
+        public PlateSizeResult SnapToStandardSize(PlateSizeOptions options = null)
+        {
+            if (Parts.Count == 0)
+                return default;
+
+            var bounds = Parts.GetBoundingBox();
+
+            // Quadrant-aware extents relative to the plate origin, matching AutoSize.
+            double xExtent;
+            double yExtent;
+
+            switch (Quadrant)
+            {
+                case 1:
+                    xExtent = System.Math.Abs(bounds.Right) + EdgeSpacing.Right;
+                    yExtent = System.Math.Abs(bounds.Top) + EdgeSpacing.Top;
+                    break;
+
+                case 2:
+                    xExtent = System.Math.Abs(bounds.Left) + EdgeSpacing.Left;
+                    yExtent = System.Math.Abs(bounds.Top) + EdgeSpacing.Top;
+                    break;
+
+                case 3:
+                    xExtent = System.Math.Abs(bounds.Left) + EdgeSpacing.Left;
+                    yExtent = System.Math.Abs(bounds.Bottom) + EdgeSpacing.Bottom;
+                    break;
+
+                case 4:
+                    xExtent = System.Math.Abs(bounds.Right) + EdgeSpacing.Right;
+                    yExtent = System.Math.Abs(bounds.Bottom) + EdgeSpacing.Bottom;
+                    break;
+
+                default:
+                    return default;
+            }
+
+            // PlateSizes.Recommend takes (short, long); canonicalize then map
+            // the result back so the plate's long axis stays aligned with the
+            // parts' long axis.
+            var shortDim = System.Math.Min(xExtent, yExtent);
+            var longDim = System.Math.Max(xExtent, yExtent);
+            var result = PlateSizes.Recommend(shortDim, longDim, options);
+
+            // Plate convention: Length = X axis, Width = Y axis.
+            if (xExtent >= yExtent)
+                Size = new Size(result.Width, result.Length);   // X is the long axis
+            else
+                Size = new Size(result.Length, result.Width);   // Y is the long axis
+
+            return result;
+        }
+
         /// <summary>
         /// Gets the area of the top surface of the plate.
         /// </summary>

OpenNest.Core/Shapes/PlateSizes.cs

@@ -0,0 +1,255 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using OpenNest.Geometry;
+
+namespace OpenNest.Shapes
+{
+    /// <summary>
+    /// Catalog of standard mill sheet sizes (inches) with helpers for matching
+    /// a bounding box to a recommended plate size. Uses the project-wide
+    /// (Width, Length) convention where Width is the short dimension and
+    /// Length is the long dimension.
+    /// </summary>
+    public static class PlateSizes
+    {
+        public readonly record struct Entry(string Label, double Width, double Length)
+        {
+            public double Area => Width * Length;
+
+            /// <summary>
+            /// Returns true if a part of the given dimensions fits within this entry
+            /// in either orientation.
+            /// </summary>
+            public bool Fits(double width, double length) =>
+                (width <= Width && length <= Length) || (width <= Length && length <= Width);
+        }
+
+        /// <summary>
+        /// Standard mill sheet sizes (inches), sorted by area ascending.
+        /// Canonical orientation: Width &lt;= Length.
+        /// </summary>
+        public static IReadOnlyList<Entry> All { get; } = new[]
+        {
+            new Entry("48x96",   48,  96),   // 4608
+            new Entry("48x120",  48, 120),   // 5760
+            new Entry("48x144",  48, 144),   // 6912
+            new Entry("60x120",  60, 120),   // 7200
+            new Entry("60x144",  60, 144),   // 8640
+            new Entry("72x120",  72, 120),   // 8640
+            new Entry("72x144",  72, 144),   // 10368
+            new Entry("96x240",  96, 240),   // 23040
+        };
+
+        /// <summary>
+        /// Looks up a standard size by label. Case-insensitive.
+        /// </summary>
+        public static bool TryGet(string label, out Entry entry)
+        {
+            if (!string.IsNullOrWhiteSpace(label))
+            {
+                foreach (var candidate in All)
+                {
+                    if (string.Equals(candidate.Label, label, StringComparison.OrdinalIgnoreCase))
+                    {
+                        entry = candidate;
+                        return true;
+                    }
+                }
+            }
+
+            entry = default;
+            return false;
+        }
+
+        /// <summary>
+        /// Recommends a plate size for the given bounding box. The box's
+        /// spatial axes are normalized to (short, long) so neither the bbox
+        /// orientation nor Box's internal Length/Width naming matters.
+        /// </summary>
+        public static PlateSizeResult Recommend(Box bbox, PlateSizeOptions options = null)
+        {
+            var a = bbox.Width;
+            var b = bbox.Length;
+            return Recommend(System.Math.Min(a, b), System.Math.Max(a, b), options);
+        }
+
+        /// <summary>
+        /// Recommends a plate size for the envelope of the given boxes.
+        /// </summary>
+        public static PlateSizeResult Recommend(IEnumerable<Box> boxes, PlateSizeOptions options = null)
+        {
+            if (boxes == null)
+                throw new ArgumentNullException(nameof(boxes));
+
+            var hasAny = false;
+            var minX = double.PositiveInfinity;
+            var minY = double.PositiveInfinity;
+            var maxX = double.NegativeInfinity;
+            var maxY = double.NegativeInfinity;
+
+            foreach (var box in boxes)
+            {
+                hasAny = true;
+                if (box.Left < minX) minX = box.Left;
+                if (box.Bottom < minY) minY = box.Bottom;
+                if (box.Right > maxX) maxX = box.Right;
+                if (box.Top > maxY) maxY = box.Top;
+            }
+
+            if (!hasAny)
+                throw new ArgumentException("At least one box is required.", nameof(boxes));
+
+            var b = maxX - minX;
+            var a = maxY - minY;
+            return Recommend(System.Math.Min(a, b), System.Math.Max(a, b), options);
+        }
+
+        /// <summary>
+        /// Recommends a plate size for a (width, length) pair.
+        /// Inputs are treated as orientation-independent.
+        /// </summary>
+        public static PlateSizeResult Recommend(double width, double length, PlateSizeOptions options = null)
+        {
+            options ??= new PlateSizeOptions();
+
+            var w = width + 2 * options.Margin;
+            var l = length + 2 * options.Margin;
+
+            // Canonicalize (short, long) — Fits handles rotation anyway, but
+            // normalizing lets the below-min comparison use the narrower
+            // MinSheet dimensions consistently.
+            if (w > l)
+                (w, l) = (l, w);
+
+            // Below full-sheet threshold: snap each dimension up to the nearest increment.
+            if (w <= options.MinSheetWidth && l <= options.MinSheetLength)
+                return SnapResult(w, l, options.SnapIncrement);
+
+            var catalog = BuildCatalog(options.AllowedSizes);
+
+            var best = PickBest(catalog, w, l, options.Selection);
+            if (best.HasValue)
+                return new PlateSizeResult(best.Value.Width, best.Value.Length, best.Value.Label);
+
+            // Nothing in the catalog fits - fall back to snap-up (ad-hoc oversize sheet).
+            return SnapResult(w, l, options.SnapIncrement);
+        }
+
+        private static PlateSizeResult SnapResult(double width, double length, double increment)
+        {
+            if (increment <= 0)
+                return new PlateSizeResult(width, length, null);
+
+            return new PlateSizeResult(SnapUp(width, increment), SnapUp(length, increment), null);
+        }
+
+        private static double SnapUp(double value, double increment)
+        {
+            var steps = System.Math.Ceiling(value / increment);
+            return steps * increment;
+        }
+
+        private static IReadOnlyList<Entry> BuildCatalog(IReadOnlyList<string> allowedSizes)
+        {
+            if (allowedSizes == null || allowedSizes.Count == 0)
+                return All;
+
+            var result = new List<Entry>(allowedSizes.Count);
+            foreach (var label in allowedSizes)
+            {
+                if (TryParseEntry(label, out var entry))
+                    result.Add(entry);
+            }
+
+            return result;
+        }
+
+        private static bool TryParseEntry(string label, out Entry entry)
+        {
+            if (TryGet(label, out entry))
+                return true;
+
+            // Accept ad-hoc "WxL" strings (e.g. "50x100", "50 x 100").
+            if (!string.IsNullOrWhiteSpace(label))
+            {
+                var parts = label.Split(new[] { 'x', 'X' }, 2);
+                if (parts.Length == 2
+                    && double.TryParse(parts[0].Trim(), System.Globalization.NumberStyles.Float, System.Globalization.CultureInfo.InvariantCulture, out var a)
+                    && double.TryParse(parts[1].Trim(), System.Globalization.NumberStyles.Float, System.Globalization.CultureInfo.InvariantCulture, out var b)
+                    && a > 0 && b > 0)
+                {
+                    var width = System.Math.Min(a, b);
+                    var length = System.Math.Max(a, b);
+                    entry = new Entry(label.Trim(), width, length);
+                    return true;
+                }
+            }
+
+            entry = default;
+            return false;
+        }
+
+        private static Entry? PickBest(IReadOnlyList<Entry> catalog, double width, double length, PlateSizeSelection selection)
+        {
+            var fitting = catalog.Where(e => e.Fits(width, length));
+
+            fitting = selection switch
+            {
+                PlateSizeSelection.NarrowestFirst => fitting.OrderBy(e => e.Width).ThenBy(e => e.Area),
+                _ => fitting.OrderBy(e => e.Area).ThenBy(e => e.Width),
+            };
+
+            foreach (var candidate in fitting)
+                return candidate;
+
+            return null;
+        }
+    }
+
+    public readonly record struct PlateSizeResult(double Width, double Length, string MatchedLabel)
+    {
+        public bool IsStandard => MatchedLabel != null;
+    }
+
+    public sealed class PlateSizeOptions
+    {
+        /// <summary>
+        /// If the margin-adjusted bounding box fits within MinSheetWidth x MinSheetLength
+        /// the result is snapped to <see cref="SnapIncrement"/> instead of routed to a
+        /// standard sheet. Default 48" x 48".
+        /// </summary>
+        public double MinSheetWidth { get; set; } = 48;
+        public double MinSheetLength { get; set; } = 48;
+
+        /// <summary>
+        /// Increment used for below-threshold rounding and oversize fallback. Default 1".
+        /// </summary>
+        public double SnapIncrement { get; set; } = 1.0;
+
+        /// <summary>
+        /// Extra clearance added to each side of the bounding box before matching.
+        /// </summary>
+        public double Margin { get; set; } = 0;
+
+        /// <summary>
+        /// Optional whitelist. When non-empty, only these sizes are considered.
+        /// Entries may be standard catalog labels (e.g. "48x96") or arbitrary
+        /// "WxL" strings (e.g. "50x100").
+        /// </summary>
+        public IReadOnlyList<string> AllowedSizes { get; set; }
+
+        /// <summary>
+        /// Tiebreaker when multiple sheets can contain the bounding box.
+        /// </summary>
+        public PlateSizeSelection Selection { get; set; } = PlateSizeSelection.SmallestArea;
+    }
+
+    public enum PlateSizeSelection
+    {
+        /// <summary>Pick the cheapest sheet that contains the bbox (smallest area).</summary>
+        SmallestArea,
+        /// <summary>Prefer narrower-width sheets (e.g. 48-wide before 60-wide).</summary>
+        NarrowestFirst,
+    }
+}

OpenNest.Tests/PlateSnapToStandardSizeTests.cs

@@ -0,0 +1,118 @@
+using OpenNest.CNC;
+using OpenNest.Geometry;
+using OpenNest.Shapes;
+
+namespace OpenNest.Tests;
+
+public class PlateSnapToStandardSizeTests
+{
+    private static Part MakeRectPart(double x, double y, double length, double width)
+    {
+        var pgm = new Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(length, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(length, width)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, width)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 0)));
+        var drawing = new Drawing("test", pgm);
+        var part = new Part(drawing);
+        part.Offset(x, y);
+        return part;
+    }
+
+    [Fact]
+    public void SnapToStandardSize_SmallParts_SnapsToIncrement()
+    {
+        var plate = new Plate(200, 200); // oversized starting size
+        plate.Parts.Add(MakeRectPart(0, 0, 10, 20));
+
+        var result = plate.SnapToStandardSize();
+
+        // 10x20 is well below 48x48 MinSheet -> snap to integer increment.
+        Assert.Null(result.MatchedLabel);
+        Assert.Equal(10, plate.Size.Length); // X axis
+        Assert.Equal(20, plate.Size.Width);  // Y axis
+    }
+
+    [Fact]
+    public void SnapToStandardSize_SmallPartsWithFractionalIncrement_UsesIncrement()
+    {
+        var plate = new Plate(200, 200);
+        plate.Parts.Add(MakeRectPart(0, 0, 10.3, 20.7));
+
+        var result = plate.SnapToStandardSize(new PlateSizeOptions { SnapIncrement = 0.25 });
+
+        Assert.Null(result.MatchedLabel);
+        Assert.Equal(10.5, plate.Size.Length, 4);
+        Assert.Equal(20.75, plate.Size.Width, 4);
+    }
+
+    [Fact]
+    public void SnapToStandardSize_40x90Part_SnapsToStandard48x96_XLong()
+    {
+        // Part is 90 long (X) x 40 wide (Y) -> X is the long axis.
+        var plate = new Plate(200, 200);
+        plate.Parts.Add(MakeRectPart(0, 0, 90, 40));
+
+        var result = plate.SnapToStandardSize();
+
+        Assert.Equal("48x96", result.MatchedLabel);
+        Assert.Equal(96, plate.Size.Length); // X axis = long
+        Assert.Equal(48, plate.Size.Width);  // Y axis = short
+    }
+
+    [Fact]
+    public void SnapToStandardSize_90TallPart_SnapsToStandard48x96_YLong()
+    {
+        // Part is 40 long (X) x 90 wide (Y) -> Y is the long axis.
+        var plate = new Plate(200, 200);
+        plate.Parts.Add(MakeRectPart(0, 0, 40, 90));
+
+        var result = plate.SnapToStandardSize();
+
+        Assert.Equal("48x96", result.MatchedLabel);
+        Assert.Equal(48, plate.Size.Length); // X axis = short
+        Assert.Equal(96, plate.Size.Width);  // Y axis = long
+    }
+
+    [Fact]
+    public void SnapToStandardSize_JustOver48_PicksNextStandardSize()
+    {
+        var plate = new Plate(200, 200);
+        plate.Parts.Add(MakeRectPart(0, 0, 100, 50));
+
+        var result = plate.SnapToStandardSize();
+
+        Assert.Equal("60x120", result.MatchedLabel);
+        Assert.Equal(120, plate.Size.Length); // X long
+        Assert.Equal(60, plate.Size.Width);
+    }
+
+    [Fact]
+    public void SnapToStandardSize_EmptyPlate_DoesNotModifySize()
+    {
+        var plate = new Plate(60, 120);
+
+        var result = plate.SnapToStandardSize();
+
+        Assert.Null(result.MatchedLabel);
+        Assert.Equal(60, plate.Size.Width);
+        Assert.Equal(120, plate.Size.Length);
+    }
+
+    [Fact]
+    public void SnapToStandardSize_MultipleParts_UsesCombinedEnvelope()
+    {
+        var plate = new Plate(200, 200);
+        plate.Parts.Add(MakeRectPart(0, 0, 30, 40));
+        plate.Parts.Add(MakeRectPart(30, 0, 30, 40));  // combined X-extent = 60
+        plate.Parts.Add(MakeRectPart(0, 40, 60, 60));  // combined extent = 60 x 100
+
+        var result = plate.SnapToStandardSize();
+
+        // 60 x 100 fits 60x120 standard sheet, Y is the long axis.
+        Assert.Equal("60x120", result.MatchedLabel);
+        Assert.Equal(60, plate.Size.Length); // X
+        Assert.Equal(120, plate.Size.Width); // Y long
+    }
+}

OpenNest.Tests/Shapes/PlateSizesTests.cs

@@ -0,0 +1,311 @@
+using System.Collections.Generic;
+using System.Linq;
+using OpenNest.Geometry;
+using OpenNest.Shapes;
+
+namespace OpenNest.Tests.Shapes;
+
+public class PlateSizesTests
+{
+    [Fact]
+    public void All_IsNotEmpty()
+    {
+        Assert.NotEmpty(PlateSizes.All);
+    }
+
+    [Fact]
+    public void All_DoesNotContain48x48()
+    {
+        // 48x48 is not a standard sheet - it's the default MinSheet threshold only.
+        Assert.DoesNotContain(PlateSizes.All, e => e.Width == 48 && e.Length == 48);
+    }
+
+    [Fact]
+    public void All_Smallest_Is48x96()
+    {
+        var smallest = PlateSizes.All.OrderBy(e => e.Area).First();
+        Assert.Equal(48, smallest.Width);
+        Assert.Equal(96, smallest.Length);
+    }
+
+    [Fact]
+    public void All_SortedByAreaAscending()
+    {
+        for (var i = 1; i < PlateSizes.All.Count; i++)
+            Assert.True(PlateSizes.All[i].Area >= PlateSizes.All[i - 1].Area);
+    }
+
+    [Fact]
+    public void All_Entries_AreCanonical_WidthLessOrEqualLength()
+    {
+        foreach (var entry in PlateSizes.All)
+            Assert.True(entry.Width <= entry.Length, $"{entry.Label} not in canonical orientation");
+    }
+
+    [Theory]
+    [InlineData(40, 40, true)]    // small - fits trivially
+    [InlineData(48, 96, true)]    // exact
+    [InlineData(96, 48, true)]    // rotated exact
+    [InlineData(90, 40, true)]    // rotated
+    [InlineData(49, 97, false)]   // just over in both dims
+    [InlineData(50, 50, false)]   // too wide in both orientations
+    public void Entry_Fits_RespectsRotation(double w, double h, bool expected)
+    {
+        var entry = new PlateSizes.Entry("48x96", 48, 96);
+        Assert.Equal(expected, entry.Fits(w, h));
+    }
+
+    [Fact]
+    public void TryGet_KnownLabel_ReturnsEntry()
+    {
+        Assert.True(PlateSizes.TryGet("48x96", out var entry));
+        Assert.Equal(48, entry.Width);
+        Assert.Equal(96, entry.Length);
+    }
+
+    [Fact]
+    public void TryGet_IsCaseInsensitive()
+    {
+        Assert.True(PlateSizes.TryGet("48X96", out var entry));
+        Assert.Equal(48, entry.Width);
+        Assert.Equal(96, entry.Length);
+    }
+
+    [Fact]
+    public void TryGet_UnknownLabel_ReturnsFalse()
+    {
+        Assert.False(PlateSizes.TryGet("bogus", out _));
+    }
+
+    [Fact]
+    public void Recommend_BelowMin_SnapsToDefaultIncrementOfOne()
+    {
+        var bbox = new Box(0, 0, 10.3, 20.7);
+
+        var result = PlateSizes.Recommend(bbox);
+
+        Assert.Equal(11, result.Width);
+        Assert.Equal(21, result.Length);
+        Assert.Null(result.MatchedLabel);
+    }
+
+    [Fact]
+    public void Recommend_BelowMin_UsesCustomIncrement()
+    {
+        var bbox = new Box(0, 0, 10.3, 20.7);
+        var options = new PlateSizeOptions { SnapIncrement = 0.25 };
+
+        var result = PlateSizes.Recommend(bbox, options);
+
+        Assert.Equal(10.5, result.Width, 4);
+        Assert.Equal(20.75, result.Length, 4);
+        Assert.Null(result.MatchedLabel);
+    }
+
+    [Fact]
+    public void Recommend_ExactlyAtMin_Snaps()
+    {
+        var bbox = new Box(0, 0, 48, 48);
+
+        var result = PlateSizes.Recommend(bbox);
+
+        Assert.Equal(48, result.Width);
+        Assert.Equal(48, result.Length);
+        Assert.Null(result.MatchedLabel);
+    }
+
+    [Fact]
+    public void Recommend_AboveMin_PicksSmallestContainingStandardSheet()
+    {
+        var bbox = new Box(0, 0, 40, 90);
+
+        var result = PlateSizes.Recommend(bbox);
+
+        Assert.Equal(48, result.Width);
+        Assert.Equal(96, result.Length);
+        Assert.Equal("48x96", result.MatchedLabel);
+    }
+
+    [Fact]
+    public void Recommend_AboveMin_WithRotation_PicksSmallestSheet()
+    {
+        var bbox = new Box(0, 0, 90, 40);
+
+        var result = PlateSizes.Recommend(bbox);
+
+        Assert.Equal("48x96", result.MatchedLabel);
+    }
+
+    [Fact]
+    public void Recommend_JustOver48_PicksNextStandardSize()
+    {
+        var bbox = new Box(0, 0, 50, 100);
+
+        var result = PlateSizes.Recommend(bbox);
+
+        Assert.Equal(60, result.Width);
+        Assert.Equal(120, result.Length);
+        Assert.Equal("60x120", result.MatchedLabel);
+    }
+
+    [Fact]
+    public void Recommend_MarginIsAppliedPerSide()
+    {
+        // 46 + 2*1 = 48 (fits exactly), 94 + 2*1 = 96 (fits exactly)
+        var bbox = new Box(0, 0, 46, 94);
+        var options = new PlateSizeOptions { Margin = 1 };
+
+        var result = PlateSizes.Recommend(bbox, options);
+
+        Assert.Equal("48x96", result.MatchedLabel);
+    }
+
+    [Fact]
+    public void Recommend_MarginPushesToNextSheet()
+    {
+        // 47 + 2 = 49 > 48, so 48x96 no longer fits -> next standard
+        var bbox = new Box(0, 0, 47, 95);
+        var options = new PlateSizeOptions { Margin = 1 };
+
+        var result = PlateSizes.Recommend(bbox, options);
+
+        Assert.NotEqual("48x96", result.MatchedLabel);
+        Assert.True(result.Width >= 49);
+        Assert.True(result.Length >= 97);
+    }
+
+    [Fact]
+    public void Recommend_AllowedSizes_StandardLabelWhitelist()
+    {
+        // 60x120 is the only option; 50x50 is above min so it routes to standard
+        var bbox = new Box(0, 0, 50, 50);
+        var options = new PlateSizeOptions { AllowedSizes = new[] { "60x120" } };
+
+        var result = PlateSizes.Recommend(bbox, options);
+
+        Assert.Equal("60x120", result.MatchedLabel);
+    }
+
+    [Fact]
+    public void Recommend_AllowedSizes_ArbitraryWxHString()
+    {
+        // 50x100 isn't in the standard catalog but is valid as an ad-hoc entry.
+        // bbox 49x99 doesn't fit 48x96 or 48x120, does fit 50x100 and 60x120,
+        // but only 50x100 is allowed.
+        var bbox = new Box(0, 0, 49, 99);
+        var options = new PlateSizeOptions { AllowedSizes = new[] { "50x100" } };
+
+        var result = PlateSizes.Recommend(bbox, options);
+
+        Assert.Equal(50, result.Width);
+        Assert.Equal(100, result.Length);
+        Assert.Equal("50x100", result.MatchedLabel);
+    }
+
+    [Fact]
+    public void Recommend_NothingFits_FallsBackToSnapUp()
+    {
+        // Larger than any catalog sheet
+        var bbox = new Box(0, 0, 100, 300);
+
+        var result = PlateSizes.Recommend(bbox);
+
+        Assert.Equal(100, result.Width);
+        Assert.Equal(300, result.Length);
+        Assert.Null(result.MatchedLabel);
+    }
+
+    [Fact]
+    public void Recommend_NothingFitsInAllowedList_FallsBackToSnapUp()
+    {
+        // Only 48x96 allowed, but bbox is too big for it
+        var bbox = new Box(0, 0, 50, 100);
+        var options = new PlateSizeOptions { AllowedSizes = new[] { "48x96" } };
+
+        var result = PlateSizes.Recommend(bbox, options);
+
+        Assert.Equal(50, result.Width);
+        Assert.Equal(100, result.Length);
+        Assert.Null(result.MatchedLabel);
+    }
+
+    [Fact]
+    public void Recommend_BoxEnumerable_CombinesIntoEnvelope()
+    {
+        // Two boxes that together span 0..40 x 0..90 -> fits 48x96
+        var boxes = new[]
+        {
+            new Box(0, 0, 40, 50),
+            new Box(0, 40, 30, 50),
+        };
+
+        var result = PlateSizes.Recommend(boxes);
+
+        Assert.Equal("48x96", result.MatchedLabel);
+    }
+
+    [Fact]
+    public void Recommend_BoxEnumerable_Empty_Throws()
+    {
+        Assert.Throws<System.ArgumentException>(
+            () => PlateSizes.Recommend(System.Array.Empty<Box>()));
+    }
+
+    [Fact]
+    public void PlateSizeOptions_Defaults()
+    {
+        var options = new PlateSizeOptions();
+
+        Assert.Equal(48, options.MinSheetWidth);
+        Assert.Equal(48, options.MinSheetLength);
+        Assert.Equal(1.0, options.SnapIncrement);
+        Assert.Equal(0, options.Margin);
+        Assert.Null(options.AllowedSizes);
+        Assert.Equal(PlateSizeSelection.SmallestArea, options.Selection);
+    }
+
+    [Fact]
+    public void Recommend_NarrowestFirst_PicksNarrowerSheetOverSmallerArea()
+    {
+        // Hypothetical: bbox (47, 47) fits both 48x96 (area 4608) and some narrower option.
+        // With SmallestArea: picks 48x96 (it's already the smallest 48-wide).
+        // With NarrowestFirst: also picks 48x96 since that's the narrowest.
+        // Better test: AllowedSizes = ["60x120", "48x120"] with bbox that fits both.
+        // 48x120 (area 5760) is narrower; 60x120 (area 7200) has more area.
+        // SmallestArea picks 48x120; NarrowestFirst also picks 48x120. Both pick the same.
+        //
+        // Real divergence: AllowedSizes = ["60x120", "72x120"] with bbox 55x100.
+        // 60x120 has narrower width (60) AND smaller area (7200 vs 8640), so both agree.
+        //
+        // To force divergence: AllowedSizes = ["60x96", "48x144"] with bbox 47x95.
+        // 60x96 area = 5760, 48x144 area = 6912. SmallestArea -> 60x96.
+        // NarrowestFirst width 48 < 60 -> 48x144.
+        var bbox = new Box(0, 0, 47, 95);
+        var options = new PlateSizeOptions
+        {
+            AllowedSizes = new[] { "60x96", "48x144" },
+            Selection = PlateSizeSelection.NarrowestFirst,
+        };
+
+        var result = PlateSizes.Recommend(bbox, options);
+
+        Assert.Equal(48, result.Width);
+        Assert.Equal(144, result.Length);
+    }
+
+    [Fact]
+    public void Recommend_SmallestArea_PicksSmallerAreaOverNarrowerWidth()
+    {
+        var bbox = new Box(0, 0, 47, 95);
+        var options = new PlateSizeOptions
+        {
+            AllowedSizes = new[] { "60x96", "48x144" },
+            Selection = PlateSizeSelection.SmallestArea,
+        };
+
+        var result = PlateSizes.Recommend(bbox, options);
+
+        Assert.Equal(60, result.Width);
+        Assert.Equal(96, result.Length);
+    }
+}

OpenNest/Forms/EditNestForm.cs

@@ -7,6 +7,7 @@ using OpenNest.Engine.Sequencing;
 using OpenNest.IO;
 using OpenNest.Math;
 using OpenNest.Properties;
+using OpenNest.Shapes;
 using System;
 using System.ComponentModel;
 using System.Diagnostics;
@@ -453,7 +454,11 @@ namespace OpenNest.Forms
 
         public void ResizePlateToFitParts()
         {
-            PlateView.Plate.AutoSize(Settings.Default.AutoSizePlateFactor);
+            var options = new PlateSizeOptions
+            {
+                SnapIncrement = Settings.Default.AutoSizePlateFactor,
+            };
+            PlateView.Plate.SnapToStandardSize(options);
             PlateView.ZoomToPlate();
             PlateView.Refresh();
             UpdatePlateList();