feat(ui): populate material combobox from post processors

Replaces the material textbox on EditNestInfoForm with a combobox whose
items are aggregated from every loaded post processor that implements the
new IMaterialProvidingPostProcessor interface. CincinnatiPostProcessor
exposes its configured MaterialLibraries entries. Free-text entry still
works so custom materials remain usable.

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

OpenNest.Core/IMaterialProvidingPostProcessor.cs

@@ -0,0 +1,9 @@
+using System.Collections.Generic;
+
+namespace OpenNest
+{
+    public interface IMaterialProvidingPostProcessor
+    {
+        IEnumerable<string> GetMaterialNames();
+    }
+}

OpenNest.Posts.Cincinnati/CincinnatiPostProcessor.cs

@@ -9,7 +9,7 @@ using OpenNest.CNC;
 
 namespace OpenNest.Posts.Cincinnati
 {
-    public sealed class CincinnatiPostProcessor : IConfigurablePostProcessor
+    public sealed class CincinnatiPostProcessor : IConfigurablePostProcessor, IMaterialProvidingPostProcessor
     {
         private static readonly JsonSerializerOptions JsonOptions = new()
         {
@@ -25,6 +25,16 @@ namespace OpenNest.Posts.Cincinnati
 
         object IConfigurablePostProcessor.Config => Config;
 
+        public IEnumerable<string> GetMaterialNames()
+        {
+            if (Config?.MaterialLibraries == null)
+                return System.Array.Empty<string>();
+
+            return Config.MaterialLibraries
+                .Select(e => e.Material)
+                .Where(s => !string.IsNullOrWhiteSpace(s));
+        }
+
         public CincinnatiPostProcessor()
         {
             var configPath = GetConfigPath();

OpenNest/Forms/EditNestInfoForm.Designer.cs

@@ -63,7 +63,7 @@
             this.textBox2 = new System.Windows.Forms.TextBox();
             this.label5 = new System.Windows.Forms.Label();
             this.labelMaterial = new System.Windows.Forms.Label();
-            this.materialBox = new System.Windows.Forms.TextBox();
+            this.materialBox = new System.Windows.Forms.ComboBox();
             this.tabPage2 = new System.Windows.Forms.TabPage();
             this.tabPage3 = new System.Windows.Forms.TabPage();
             this.notesBox = new System.Windows.Forms.TextBox();
@@ -516,9 +516,10 @@
             // materialBox
             //
             this.materialBox.Anchor = ((System.Windows.Forms.AnchorStyles)((System.Windows.Forms.AnchorStyles.Left | System.Windows.Forms.AnchorStyles.Right)));
+            this.materialBox.FormattingEnabled = true;
             this.materialBox.Location = new System.Drawing.Point(135, 159);
             this.materialBox.Name = "materialBox";
-            this.materialBox.Size = new System.Drawing.Size(224, 22);
+            this.materialBox.Size = new System.Drawing.Size(224, 24);
             this.materialBox.TabIndex = 11;
             //
             // label3
@@ -729,6 +730,6 @@
         private System.Windows.Forms.RadioButton radioButton2;
         private System.Windows.Forms.Label label5;
         private System.Windows.Forms.Label labelMaterial;
-        private System.Windows.Forms.TextBox materialBox;
+        private System.Windows.Forms.ComboBox materialBox;
     }
 }

OpenNest/Forms/EditNestInfoForm.cs

@@ -15,6 +15,9 @@ namespace OpenNest.Forms
         {
             InitializeComponent();
 
+            foreach (var name in PostProcessorMaterials.Names)
+                materialBox.Items.Add(name);
+
             timer = new Timer
             {
                 SynchronizingObject = this,

OpenNest/Forms/MainForm.cs

@@ -351,6 +351,9 @@ namespace OpenNest.Forms
                         postProcessorMenuItem.Tag = postProcessor;
                         postProcessorMenuItem.Click += PostProcessor_Click;
                         mnuNestPost.DropDownItems.Add(postProcessorMenuItem);
+
+                        if (postProcessor is IMaterialProvidingPostProcessor materialProvider)
+                            PostProcessorMaterials.AddFrom(materialProvider);
                     }
                 }
             }
@@ -1157,6 +1160,9 @@ namespace OpenNest.Forms
             if (postProcessor == null)
                 return;
 
+            if (postProcessor is IPostProcessorNestAware nestAware)
+                nestAware.PrepareForNest(activeForm.Nest);
+
             if (postProcessor is IConfigurablePostProcessor configurable)
             {
                 using var configForm = new PostProcessorConfigForm(configurable);

OpenNest/PostProcessorMaterials.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace OpenNest
+{
+    public static class PostProcessorMaterials
+    {
+        private static readonly List<string> materials = new();
+
+        public static IReadOnlyList<string> Names => materials;
+
+        public static void AddFrom(IMaterialProvidingPostProcessor provider)
+        {
+            if (provider == null)
+                return;
+
+            foreach (var name in provider.GetMaterialNames())
+            {
+                if (!string.IsNullOrWhiteSpace(name)
+                    && !materials.Contains(name, StringComparer.OrdinalIgnoreCase))
+                {
+                    materials.Add(name);
+                }
+            }
+
+            materials.Sort(StringComparer.OrdinalIgnoreCase);
+        }
+    }
+}