refactor(io): migrate nest file extension from .zip to .opnest

Add FileExtension and FileFilter constants to NestFormat and update all
references across Console, MCP, Training, and WinForms projects.

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

OpenNest.Console/Program.cs

@@ -152,7 +152,8 @@ static class NestConsole
     static Nest LoadOrCreateNest(Options options)
     {
         var nestFile = options.InputFiles.FirstOrDefault(f =>
-            f.EndsWith(".zip", StringComparison.OrdinalIgnoreCase));
+            f.EndsWith(NestFormat.FileExtension, StringComparison.OrdinalIgnoreCase)
+            || f.EndsWith(".zip", StringComparison.OrdinalIgnoreCase));
         var dxfFiles = options.InputFiles.Where(f =>
             f.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase)).ToList();
 
@@ -190,7 +191,7 @@ static class NestConsole
         // DXF-only mode: create a fresh nest.
         if (dxfFiles.Count == 0)
         {
-            Console.Error.WriteLine("Error: no nest (.zip) or DXF (.dxf) files specified");
+            Console.Error.WriteLine("Error: no nest (.opnest) or DXF (.dxf) files specified");
             return null;
         }
 
@@ -272,7 +273,9 @@ static class NestConsole
             plate.PartSpacing = options.Spacing.Value;
 
         // Only apply size override when it wasn't already used to create the plate.
-        var hasDxfOnly = !options.InputFiles.Any(f => f.EndsWith(".zip", StringComparison.OrdinalIgnoreCase));
+        var hasDxfOnly = !options.InputFiles.Any(f =>
+            f.EndsWith(NestFormat.FileExtension, StringComparison.OrdinalIgnoreCase)
+            || f.EndsWith(".zip", StringComparison.OrdinalIgnoreCase));
 
         if (options.PlateSize.HasValue && !hasDxfOnly)
             plate.Size = options.PlateSize.Value;
@@ -373,7 +376,7 @@ static class NestConsole
         var firstInput = options.InputFiles[0];
         var outputFile = options.OutputFile ?? Path.Combine(
             Path.GetDirectoryName(firstInput),
-            $"{Path.GetFileNameWithoutExtension(firstInput)}-result.zip");
+            $"{Path.GetFileNameWithoutExtension(firstInput)}-result{NestFormat.FileExtension}");
 
         new NestWriter(nest).Write(outputFile);
         Console.WriteLine($"Saved: {outputFile}");
@@ -384,12 +387,12 @@ static class NestConsole
         Console.Error.WriteLine("Usage: OpenNest.Console <input-files...> [options]");
         Console.Error.WriteLine();
         Console.Error.WriteLine("Arguments:");
-        Console.Error.WriteLine("  input-files            One or more .zip nest files or .dxf drawing files");
+        Console.Error.WriteLine("  input-files            One or more .opnest nest files or .dxf drawing files");
         Console.Error.WriteLine();
         Console.Error.WriteLine("Modes:");
-        Console.Error.WriteLine("  <nest.zip>             Load nest and fill (existing behavior)");
+        Console.Error.WriteLine("  <nest.opnest>             Load nest and fill (existing behavior)");
-        Console.Error.WriteLine("  <part.dxf> --size WxL  Import DXF, create plate, and fill");
+        Console.Error.WriteLine("  <part.dxf> --size WxL     Import DXF, create plate, and fill");
-        Console.Error.WriteLine("  <nest.zip> <part.dxf>  Load nest and add imported DXF drawings");
+        Console.Error.WriteLine("  <nest.opnest> <part.dxf>  Load nest and add imported DXF drawings");
         Console.Error.WriteLine();
         Console.Error.WriteLine("Options:");
         Console.Error.WriteLine("  --drawing <name>       Drawing name to fill with (default: first drawing)");
@@ -397,7 +400,7 @@ static class NestConsole
         Console.Error.WriteLine("  --quantity <n>          Max parts to place (default: 0 = unlimited)");
         Console.Error.WriteLine("  --spacing <value>      Override part spacing");
         Console.Error.WriteLine("  --size <WxL>           Override plate size (e.g. 60x120); required for DXF-only mode");
-        Console.Error.WriteLine("  --output <path>        Output nest file path (default: <input>-result.zip)");
+        Console.Error.WriteLine("  --output <path>        Output nest file path (default: <input>-result.opnest)");
         Console.Error.WriteLine("  --template <path>      Nest template for plate defaults (thickness, quadrant, material, spacing)");
         Console.Error.WriteLine("  --autonest             Use NFP-based mixed-part autonesting instead of linear fill");
         Console.Error.WriteLine("  --keep-parts           Don't clear existing parts before filling");

OpenNest.IO/NestFormat.cs

@@ -5,6 +5,9 @@ namespace OpenNest.IO
 {
     public static class NestFormat
     {
+        public const string FileExtension = ".opnest";
+        public const string FileFilter = "Nest Files (*.opnest)|*.opnest";
+
         public static readonly JsonSerializerOptions JsonOptions = new()
         {
             PropertyNamingPolicy = JsonNamingPolicy.CamelCase,

OpenNest.Mcp/Tools/InputTools.cs

@@ -21,8 +21,8 @@ namespace OpenNest.Mcp.Tools
         }
 
         [McpServerTool(Name = "load_nest")]
-        [Description("Load a .nest zip file into the session. Returns a summary of plates, parts, and drawings.")]
+        [Description("Load an .opnest file into the session. Returns a summary of plates, parts, and drawings.")]
-        public string LoadNest([Description("Absolute path to the .nest file")] string path)
+        public string LoadNest([Description("Absolute path to the .opnest file")] string path)
         {
             if (!File.Exists(path))
                 return $"Error: file not found: {path}";

OpenNest.Mcp/Tools/TestTools.cs

@@ -17,10 +17,10 @@ namespace OpenNest.Mcp.Tools
         [McpServerTool(Name = "test_engine")]
         [Description("Build and run the nesting engine against a nest file. Returns fill results and a debug log file path for grepping. Use this to test engine changes without restarting the MCP server.")]
         public string TestEngine(
-            [Description("Path to the nest .zip file")] string nestFile = @"C:\Users\AJ\Desktop\4980 A24 PT02 60x120  45pcs v2.zip",
+            [Description("Path to the nest .opnest file")] string nestFile = @"C:\Users\AJ\Desktop\4980 A24 PT02 60x120  45pcs v2.opnest",
             [Description("Drawing name to fill with (default: first drawing)")] string drawingName = null,
             [Description("Plate index to fill (default: 0)")] int plateIndex = 0,
-            [Description("Output nest file path (default: <input>-result.zip)")] string outputFile = null)
+            [Description("Output nest file path (default: <input>-result.opnest)")] string outputFile = null)
         {
             if (!File.Exists(nestFile))
                 return $"Error: nest file not found: {nestFile}";

OpenNest.Training/Program.cs

@@ -234,7 +234,7 @@ int RunDataCollection(string dir, string dbPath, string saveDir, double s, strin
                     Directory.CreateDirectory(partDir);
 
                     var nestName = $"{partNo}-{size.Length}x{size.Width}-{result.PartCount}pcs";
-                    var fileName = nestName + ".zip";
+                    var fileName = nestName + NestFormat.FileExtension;
                     savedFilePath = Path.Combine(partDir, fileName);
 
                     // Create nest from template or from scratch
@@ -299,7 +299,7 @@ void PrintUsage()
     Console.Error.WriteLine("Options:");
     Console.Error.WriteLine("  --spacing <value>      Part spacing (default: 0.5)");
     Console.Error.WriteLine("  --db <path>            SQLite database path (default: OpenNestTraining.db)");
-    Console.Error.WriteLine("  --save-nests <dir>     Directory to save individual .zip nests for each winner");
+    Console.Error.WriteLine("  --save-nests <dir>     Directory to save individual .opnest nests for each winner");
     Console.Error.WriteLine("  --template <path>      Nest template (.nstdot) for plate defaults");
     Console.Error.WriteLine("  -h, --help             Show this help");
 }

OpenNest/Forms/EditNestForm.cs

@@ -288,7 +288,7 @@ namespace OpenNest.Forms
         public void SaveAs()
         {
             var dlg = new SaveFileDialog();
-            dlg.Filter = "Nest Files|*.zip|Template File|*.nstdot";
+            dlg.Filter = $"{NestFormat.FileFilter}|Template File|*.nstdot";
             dlg.FileName = Nest.Name;
 
             if (dlg.ShowDialog() == System.Windows.Forms.DialogResult.OK)

OpenNest/Forms/MainForm.cs

@@ -403,7 +403,7 @@ namespace OpenNest.Forms
         private void Open_Click(object sender, EventArgs e)
         {
             var dlg = new OpenFileDialog();
-            dlg.Filter = "Nest Files (*.zip) | *.zip";
+            dlg.Filter = NestFormat.FileFilter;
             dlg.Multiselect = true;
 
             if (dlg.ShowDialog() == DialogResult.OK)