diff --git a/OpenNest.WinForms.Tests/ArchUnitsTests.cs b/OpenNest.WinForms.Tests/ArchUnitsTests.cs
new file mode 100644
index 0000000..00a121b
--- /dev/null
+++ b/OpenNest.WinForms.Tests/ArchUnitsTests.cs
@@ -0,0 +1,65 @@
+using System.Drawing;
+using System.Globalization;
+using System.Reflection;
+using System.Runtime.ExceptionServices;
+using System.Text.RegularExpressions;
+using System.Windows.Forms;
+
+namespace OpenNest.WinForms.Tests;
+
+public class ArchUnitsTests
+{
+    [Fact]
+    public void ArchitecturalRegexHasExplicitTimeout()
+    {
+        var regex = Assert.IsType<Regex>(typeof(ArchUnits)
+            .GetField("UnitRegex", BindingFlags.Static | BindingFlags.NonPublic)!.GetValue(null));
+        Assert.Equal(TimeSpan.FromMilliseconds(250), regex.MatchTimeout);
+        Assert.Equal(RegexOptions.None, regex.Options);
+    }
+
+    [Theory]
+    [InlineData("5' 6.5\"", 66.5)]
+    [InlineData("2 feet 3 1/2 inches", 27.5)]
+    [InlineData("1-1/2\"", 1.5)]
+    [InlineData("48", 48)]
+    [InlineData("", 0)]
+    public void OrdinaryArchitecturalInputsKeepTheirMeaning(string input, double expected)
+    {
+        var original = CultureInfo.CurrentCulture;
+        try
+        {
+            CultureInfo.CurrentCulture = CultureInfo.InvariantCulture;
+            Assert.Equal(expected, ArchUnits.ParseToInches(input));
+        }
+        finally { CultureInfo.CurrentCulture = original; }
+    }
+
+    [Fact]
+    public void InvalidFieldIsRedAndNaNAndCorrectionRestoresIt() => RunSta(() =>
+    {
+        using var field = new TextBox { Text = "invalid dimension" };
+        Assert.True(double.IsNaN(ArchUnits.GetLengthInches(field)));
+        Assert.Equal(Color.Red, field.ForeColor);
+        field.Text = "12\"";
+        Assert.Equal(12, ArchUnits.GetLengthInches(field));
+        Assert.Equal(SystemColors.WindowText, field.ForeColor);
+    });
+
+    // Actual timeout execution is covered by the shared Regex mechanism in FractionTests;
+    // these desktop tests deliberately avoid timing-sensitive oversized-input fixtures.
+    internal static void RunSta(Action action)
+    {
+        Exception? error = null;
+        var thread = new Thread(() =>
+        {
+            try { action(); }
+            catch (Exception ex) { error = ex; }
+        });
+        thread.SetApartmentState(ApartmentState.STA);
+        thread.Start();
+        Assert.True(thread.Join(TimeSpan.FromSeconds(15)));
+        if (error != null)
+            ExceptionDispatchInfo.Capture(error).Throw();
+    }
+}
diff --git a/OpenNest.WinForms.Tests/Forms/AutoNestFormStockOptionsTests.cs b/OpenNest.WinForms.Tests/Forms/AutoNestFormStockOptionsTests.cs
index a360f95..c4a176b 100644
--- a/OpenNest.WinForms.Tests/Forms/AutoNestFormStockOptionsTests.cs
+++ b/OpenNest.WinForms.Tests/Forms/AutoNestFormStockOptionsTests.cs
@@ -1,6 +1,8 @@
 using System.Collections;
 using System.ComponentModel;
+using System.Reflection;
 using System.Runtime.ExceptionServices;
+using System.Text.RegularExpressions;
 using System.Windows.Forms;
 using OpenNest.Forms;
 
@@ -73,6 +75,117 @@ public class AutoNestFormStockOptionsTests
         });
     }
 
+    [Fact]
+    public void StockSizeRegexHasExplicitTimeout()
+    {
+        var regex = Assert.IsType<Regex>(typeof(AutoNestForm)
+            .GetField("SizePattern", BindingFlags.Static | BindingFlags.NonPublic)!.GetValue(null));
+        Assert.Equal(TimeSpan.FromMilliseconds(250), regex.MatchTimeout);
+        Assert.Equal(RegexOptions.None, regex.Options);
+    }
+
+    [Theory]
+    [InlineData("48 x")]
+    [InlineData("abc")]
+    [InlineData("0 x 96")]
+    [InlineData("-1 x 96")]
+    [InlineData("١ x 96")]
+    public void NonblankInvalidRowRejectsWholeCollection(string invalid) => RunSta(() =>
+    {
+        using var form = new StockTestForm();
+        form.LoadPlateOptions(new List<PlateOption> { new() { Width = 48, Length = 96, Cost = 25 } }, 0.5);
+        var grid = GetGrid(form);
+        var rows = Assert.IsAssignableFrom<IBindingList>(grid.DataSource);
+        var row = rows.AddNew()!;
+        SetValue(row, "Size", invalid);
+        ((ICancelAddNew)rows).EndNew(rows.Count - 1);
+
+        Assert.False(form.TryGetPlateOptions(out var options, out var error));
+        Assert.Empty(options);
+        Assert.Contains(invalid, error);
+        Assert.Contains("row 2", error);
+        Assert.Throws<FormatException>(() => form.GetPlateOptions());
+        Assert.NotEmpty(grid.Rows[1].ErrorText);
+
+        SetValue(row, "Size", "72.5 × 144.25");
+        Assert.True(form.TryGetPlateOptions(out options, out error));
+        Assert.Null(error);
+        Assert.Equal(2, options.Count);
+        Assert.Equal(72.5, options[1].Width);
+        Assert.Equal(144.25, options[1].Length);
+        Assert.Equal(25, options[0].Cost);
+        Assert.Empty(grid.Rows[1].ErrorText);
+    });
+
+    [Fact]
+    public void TimeoutAfterValidRowPublishesNoPrefixAndDoesNotAcceptDialog() => RunSta(() =>
+    {
+        using var form = new StockTestForm();
+        form.LoadPlateOptions(new List<PlateOption> { new() { Width = 48, Length = 96 } }, 0.5);
+        var grid = GetGrid(form);
+        var rows = Assert.IsAssignableFrom<IBindingList>(grid.DataSource);
+        var row = rows.AddNew()!;
+        SetValue(row, "Size", "timeout row");
+        ((ICancelAddNew)rows).EndNew(rows.Count - 1);
+        form.FailOn = "timeout row";
+
+        Assert.False(form.TryGetPlateOptions(out var options, out var error));
+        Assert.Empty(options);
+        Assert.Contains("timeout row", error);
+        Assert.True(form.TryClose(DialogResult.OK));
+        Assert.Equal(DialogResult.None, form.DialogResult);
+        Assert.Contains("timeout row", Assert.Single(form.Notices));
+        Assert.True(form.MatchCalls > 1);
+
+        form.Notices.Clear();
+        Assert.False(form.TryClose(DialogResult.Cancel));
+        Assert.Empty(form.Notices);
+        Assert.False(Assert.IsType<Button>(form.Controls.Find("cancelButton", true).Single()).CausesValidation);
+    });
+
+    [Fact]
+    public void InvalidPendingEditCannotPublishOldBoundValue() => RunSta(() =>
+    {
+        using var form = new StockTestForm();
+        form.LoadPlateOptions(new List<PlateOption> { new() { Width = 48, Length = 96 } }, 0.5);
+        var grid = GetGrid(form);
+        form.Show();
+        grid.CurrentCell = grid.Rows[0].Cells[0];
+        Assert.True(grid.BeginEdit(false));
+        grid.EditingControl.Text = "48 x";
+
+        Assert.False(form.TryGetPlateOptions(out var options, out var error));
+        Assert.Empty(options);
+        Assert.Contains("48 x", error);
+        grid.CancelEdit();
+    });
+
+    private sealed class StockTestForm : AutoNestForm
+    {
+        public StockTestForm() : base(new Nest()) { }
+        public string? FailOn { get; set; }
+        public int MatchCalls { get; private set; }
+        public List<string> Notices { get; } = new();
+
+        internal override Match MatchStockSize(string value)
+        {
+            MatchCalls++;
+            if (value == FailOn)
+                throw new RegexMatchTimeoutException();
+            return base.MatchStockSize(value);
+        }
+
+        internal override void ReportStockValidationFailure(string error) => Notices.Add(error);
+
+        public bool TryClose(DialogResult result)
+        {
+            DialogResult = result;
+            var closing = new FormClosingEventArgs(CloseReason.UserClosing, false);
+            OnFormClosing(closing);
+            return closing.Cancel;
+        }
+    }
+
     private static DataGridView GetGrid(AutoNestForm form)
     {
         // Binding needs a context even when the test does not show the form.
diff --git a/OpenNest.WinForms.Tests/Forms/ShapeLibraryFormTests.cs b/OpenNest.WinForms.Tests/Forms/ShapeLibraryFormTests.cs
new file mode 100644
index 0000000..dad3722
--- /dev/null
+++ b/OpenNest.WinForms.Tests/Forms/ShapeLibraryFormTests.cs
@@ -0,0 +1,85 @@
+using System.Drawing;
+using System.Reflection;
+using System.Text.RegularExpressions;
+using System.Windows.Forms;
+using OpenNest.Controls;
+using OpenNest.Forms;
+using OpenNest.Shapes;
+
+namespace OpenNest.WinForms.Tests.Forms;
+
+public class ShapeLibraryFormTests
+{
+    [Fact]
+    public void FriendlyNameRegexHasExplicitTimeout()
+    {
+        var regex = Assert.IsType<Regex>(typeof(ShapeLibraryForm)
+            .GetField("FriendlyNamePattern", BindingFlags.Static | BindingFlags.NonPublic)!.GetValue(null));
+        Assert.Equal(TimeSpan.FromMilliseconds(100), regex.MatchTimeout);
+        Assert.Equal(RegexOptions.None, regex.Options);
+    }
+
+    [Theory]
+    [InlineData("PipeFlangeShape", "Pipe Flange")]
+    [InlineData("HolePatternDiameter", "Hole Pattern Diameter")]
+    [InlineData("NgonShape", "Ngon")]
+    [InlineData("ABCShape", "ABC")]
+    public void FriendlyNamesKeepSuffixAndWordBoundaryBehavior(string input, string expected)
+    {
+        Assert.Equal(expected, ShapeLibraryForm.FriendlyName(input));
+    }
+
+    [Theory]
+    [InlineData("PipeFlangeShape", "PipeFlange")]
+    [InlineData("HolePatternDiameter", "HolePatternDiameter")]
+    public void FriendlyNameTimeoutDiscardsPartialFormatting(string input, string expected)
+    {
+        var notices = new List<string>();
+        var result = ShapeLibraryForm.FriendlyName(input, name =>
+        {
+            Assert.Equal(expected, name);
+            // Simulate a replacement failing after it has transformed a prefix internally.
+            var partial = name.Insert(4, " ");
+            Assert.NotEqual(expected, partial);
+            throw new RegexMatchTimeoutException();
+        }, notices.Add);
+        Assert.Equal(expected, result);
+        Assert.Contains(expected, Assert.Single(notices));
+    }
+
+    [Fact]
+    public void InvalidShapeInputClearsOldPreviewAndBlocksAddUntilCorrected() => ArchUnitsTests.RunSta(() =>
+    {
+        using var form = new ShapeLibraryForm();
+        var list = Find<ListBox>(form, "shapeListBox");
+        list.SelectedItem = list.Items.Cast<object>().Single(entry =>
+            (Type)entry.GetType().GetProperty("ShapeType")!.GetValue(entry)! == typeof(RectangleShape));
+        var preview = Find<ShapePreviewControl>(form, "previewBox");
+        var add = Find<Button>(form, "addButton");
+        var input = Find<Panel>(form, "parametersPanel").Controls.OfType<TextBox>().First();
+        var valid = input.Text;
+        Assert.NotEmpty(preview.Plate.Parts);
+        Assert.True(add.Enabled);
+
+        input.Text = "invalid dimension";
+        Assert.Equal(Color.Red, input.ForeColor);
+        Assert.Empty(preview.Plate.Parts);
+        Assert.False(add.Enabled);
+        InvokeAdd(form);
+        Assert.Empty(form.GetDrawings());
+
+        input.Text = valid;
+        Assert.Equal(SystemColors.WindowText, input.ForeColor);
+        Assert.NotEmpty(preview.Plate.Parts);
+        Assert.True(add.Enabled);
+        InvokeAdd(form);
+        Assert.Single(form.GetDrawings());
+    });
+
+    private static T Find<T>(Control form, string name) where T : Control =>
+        Assert.IsType<T>(form.Controls.Find(name, true).Single());
+
+    private static void InvokeAdd(ShapeLibraryForm form) => typeof(ShapeLibraryForm)
+        .GetMethod("AddButton_Click", BindingFlags.Instance | BindingFlags.NonPublic)!
+        .Invoke(form, new object?[] { null, EventArgs.Empty });
+}
diff --git a/OpenNest/ArchUnits.cs b/OpenNest/ArchUnits.cs
index 5d2a6da..081fca4 100644
--- a/OpenNest/ArchUnits.cs
+++ b/OpenNest/ArchUnits.cs
@@ -10,7 +10,9 @@ namespace OpenNest
     public static class ArchUnits
     {
         private static readonly Regex UnitRegex = new Regex(
-            "^(?<Feet>\\d+\\.?\\d*\\s*')?\\s*(?<Inches>\\d+\\.?\\d*\\s*\")?$"
+            "^(?<Feet>\\d+\\.?\\d*\\s*')?\\s*(?<Inches>\\d+\\.?\\d*\\s*\")?$",
+            RegexOptions.None,
+            TimeSpan.FromMilliseconds(250)
         );
 
         public static double ParseToInches(string input)
diff --git a/OpenNest/Forms/AutoNestForm.cs b/OpenNest/Forms/AutoNestForm.cs
index 4997eb7..39ce3e1 100644
--- a/OpenNest/Forms/AutoNestForm.cs
+++ b/OpenNest/Forms/AutoNestForm.cs
@@ -10,11 +10,16 @@ namespace OpenNest.Forms
 {
     public partial class AutoNestForm : Form
     {
-        private static readonly Regex SizePattern = new(@"^(\d+\.?\d*)\s*[xX×]\s*(\d+\.?\d*)$");
+        private static readonly Regex SizePattern = new(
+            @"^(\d+\.?\d*)\s*[xX×]\s*(\d+\.?\d*)$",
+            RegexOptions.None,
+            TimeSpan.FromMilliseconds(250)
+        );
 
         public AutoNestForm(Nest nest)
         {
             InitializeComponent();
+            cancelButton.CausesValidation = false;
             SetupPartsGrid();
             SetupPlateGrid();
             LoadEngines();
@@ -195,30 +200,65 @@ namespace OpenNest.Forms
 
         public List<PlateOption> GetPlateOptions()
         {
-            plateGrid.EndEdit();
-            var result = new List<PlateOption>();
-            var gridItems = plateGrid.DataSource as BindingList<PlateOptionItem>;
-            if (gridItems == null)
-                return result;
+            if (!TryGetPlateOptions(out var options, out var error))
+                throw new FormatException(error);
+            return options;
+        }
 
-            foreach (var item in gridItems)
+        public bool TryGetPlateOptions(out List<PlateOption> options, out string error)
+        {
+            options = new List<PlateOption>();
+            error = null;
+            if (!plateGrid.EndEdit())
             {
-                if (!TryParseSize(item.Size, out var width, out var length))
-                    continue;
-                if (width <= 0 || length <= 0)
-                    continue;
-
-                result.Add(
-                    new PlateOption
-                    {
-                        Width = width,
-                        Length = length,
-                        Cost = item.Cost,
-                    }
-                );
+                var value = plateGrid.EditingControl?.Text ?? plateGrid.CurrentCell?.Value?.ToString();
+                error = $"Invalid stock size '{value}'. Enter positive dimensions as W x L.";
+                return false;
             }
 
-            return result;
+            var gridItems = plateGrid.DataSource as BindingList<PlateOptionItem>;
+            if (gridItems == null)
+                return true;
+
+            var validated = new List<PlateOption>();
+            for (var index = 0; index < gridItems.Count; index++)
+            {
+                var item = gridItems[index];
+                if (string.IsNullOrWhiteSpace(item.Size))
+                    continue;
+                if (!TryParseSize(item.Size, out var width, out var length))
+                {
+                    error = $"Invalid stock size '{item.Size}' in row {index + 1}. Enter positive dimensions as W x L.";
+                    if (index < plateGrid.Rows.Count)
+                        plateGrid.Rows[index].ErrorText = error;
+                    return false;
+                }
+
+                if (index < plateGrid.Rows.Count)
+                    plateGrid.Rows[index].ErrorText = "";
+                validated.Add(new PlateOption { Width = width, Length = length, Cost = item.Cost });
+            }
+
+            // Publish only a completely validated collection, never a valid prefix.
+            options = validated;
+            return true;
+        }
+
+        protected override void OnFormClosing(FormClosingEventArgs e)
+        {
+            if (DialogResult == DialogResult.OK && OptimizePlateSize
+                && !TryGetPlateOptions(out _, out var error))
+            {
+                e.Cancel = true;
+                DialogResult = DialogResult.None;
+                ReportStockValidationFailure(error);
+            }
+            base.OnFormClosing(e);
+        }
+
+        internal virtual void ReportStockValidationFailure(string error)
+        {
+            MessageBox.Show(this, error, "Auto Nest", MessageBoxButtons.OK, MessageBoxIcon.Warning);
         }
 
         public void LoadPlateOptions(List<PlateOption> options, double salvageRate)
@@ -300,7 +340,10 @@ namespace OpenNest.Forms
 
             var value = e.FormattedValue?.ToString();
             if (string.IsNullOrWhiteSpace(value))
+            {
+                plateGrid.Rows[e.RowIndex].ErrorText = "";
                 return;
+            }
 
             if (!TryParseSize(value, out _, out _))
             {
@@ -313,26 +356,44 @@ namespace OpenNest.Forms
             }
         }
 
-        private static bool TryParseSize(string value, out double width, out double length)
+        private bool TryParseSize(string value, out double width, out double length)
         {
             width = 0;
             length = 0;
             if (string.IsNullOrWhiteSpace(value))
                 return false;
-            var match = SizePattern.Match(value.Trim());
-            if (!match.Success)
+            try
+            {
+                var match = MatchStockSize(value.Trim());
+                if (!match.Success)
+                    return false;
+                var parsedWidth = double.Parse(
+                    match.Groups[1].Value,
+                    System.Globalization.CultureInfo.InvariantCulture
+                );
+                var parsedLength = double.Parse(
+                    match.Groups[2].Value,
+                    System.Globalization.CultureInfo.InvariantCulture
+                );
+                if (!double.IsFinite(parsedWidth) || !double.IsFinite(parsedLength)
+                    || parsedWidth <= 0 || parsedLength <= 0)
+                    return false;
+                width = parsedWidth;
+                length = parsedLength;
+                return true;
+            }
+            catch (RegexMatchTimeoutException)
+            {
                 return false;
-            width = double.Parse(
-                match.Groups[1].Value,
-                System.Globalization.CultureInfo.InvariantCulture
-            );
-            length = double.Parse(
-                match.Groups[2].Value,
-                System.Globalization.CultureInfo.InvariantCulture
-            );
-            return true;
+            }
+            catch (FormatException)
+            {
+                return false;
+            }
         }
 
+        internal virtual Match MatchStockSize(string value) => SizePattern.Match(value);
+
         private static string FormatSize(double width, double length)
         {
             return $"{width:G} x {length:G}";
diff --git a/OpenNest/Forms/MainForm.cs b/OpenNest/Forms/MainForm.cs
index 3765f11..76814e9 100644
--- a/OpenNest/Forms/MainForm.cs
+++ b/OpenNest/Forms/MainForm.cs
@@ -1381,10 +1381,15 @@ namespace OpenNest.Forms
             var items = form.GetNestItems();
             if (!items.Any(it => it.Quantity > 0))
                 return;
+            var plateOptions = default(List<PlateOption>);
+            if (form.OptimizePlateSize && !form.TryGetPlateOptions(out plateOptions, out var stockError))
+            {
+                MessageBox.Show(this, stockError, "Auto Nest", MessageBoxButtons.OK, MessageBoxIcon.Warning);
+                return;
+            }
             var engineName = form.EngineName ?? EngineSelection.EngineName;
             EngineSelection.EngineName = engineName;
             engineComboBox.SelectedItem = engineName;
-            var plateOptions = form.OptimizePlateSize ? form.GetPlateOptions() : null;
             using var cts = new CancellationTokenSource();
             nestingCts = cts;
             using var progressForm = new NestProgressForm(cts, showPlateRow: true)
diff --git a/OpenNest/Forms/ShapeLibraryForm.cs b/OpenNest/Forms/ShapeLibraryForm.cs
index e427d35..db8411a 100644
--- a/OpenNest/Forms/ShapeLibraryForm.cs
+++ b/OpenNest/Forms/ShapeLibraryForm.cs
@@ -13,6 +13,12 @@ namespace OpenNest.Forms
 {
     public partial class ShapeLibraryForm : Form
     {
+        private static readonly Regex FriendlyNamePattern = new(
+            @"(?<=[a-z0-9])([A-Z])",
+            RegexOptions.None,
+            TimeSpan.FromMilliseconds(100)
+        );
+
         private static readonly JsonSerializerOptions JsonOptions = new JsonSerializerOptions
         {
             PropertyNameCaseInsensitive = true,
@@ -272,9 +278,13 @@ namespace OpenNest.Forms
             {
                 var shape = CreateShapeFromInputs();
                 if (shape == null)
+                {
+                    InvalidatePreview();
                     return;
+                }
 
                 var drawing = shape.GetDrawing();
+                addButton.Enabled = drawing?.Program != null;
                 nameTextBox.Text = shape.GenerateName();
                 previewBox.ShowDrawing(drawing);
 
@@ -298,10 +308,17 @@ namespace OpenNest.Forms
             }
             catch
             {
-                previewBox.ShowDrawing(null);
+                InvalidatePreview();
             }
         }
 
+        private void InvalidatePreview()
+        {
+            addButton.Enabled = false;
+            previewBox.ShowDrawing(null);
+            previewBox.SetInfo("Invalid shape input");
+        }
+
         private void UpdatePipeSizeFilter()
         {
             // Find the PipeSize combo and the numeric inputs it depends on.
@@ -424,7 +441,10 @@ namespace OpenNest.Forms
             {
                 var shape = CreateShapeFromInputs();
                 if (shape == null)
+                {
+                    InvalidatePreview();
                     return;
+                }
 
                 var drawing = shape.GetDrawing();
                 drawing.Name = GetUniqueName(drawing.Name);
@@ -461,12 +481,28 @@ namespace OpenNest.Forms
             }
         }
 
-        private static string FriendlyName(string name)
+        internal static string FriendlyName(
+            string name,
+            Func<string, string> replace = null,
+            Action<string> report = null
+        )
         {
             if (name.EndsWith("Shape"))
                 name = name.Substring(0, name.Length - 5);
 
-            return Regex.Replace(name, @"(?<=[a-z0-9])([A-Z])", " $1");
+            try
+            {
+                return replace != null ? replace(name) : FriendlyNamePattern.Replace(name, " $1");
+            }
+            catch (RegexMatchTimeoutException)
+            {
+                var diagnostic = $"Friendly-name formatting timed out for '{name}'; using the unchanged name.";
+                if (report != null)
+                    report(diagnostic);
+                else
+                    System.Diagnostics.Trace.TraceWarning(diagnostic);
+                return name;
+            }
         }
 
         private class ShapeEntry