fix(ui): give console and MCP users a hint they can follow on outlined sheets

OpenNest.Console/Program.cs

@@ -24,6 +24,9 @@ return NestConsole.Run(args);
 
 static class NestConsole
 {
+    private const string OutlinedSheetMessage =
+        "Error: Fill strategies need a rectangular sheet. Use --autonest --engine Irregular.";
+
     public static int Run(string[] args)
     {
         using var cancellation = new CancellationTokenSource();
@@ -209,9 +212,9 @@ static class NestConsole
             ApplyTemplate(plate, options);
             ApplyOverrides(plate, options);
 
-            if (!options.AutoNest && PlateFillService.Refusal(plate) is { } refusal)
+            if (!options.AutoNest && PlateFillService.Refusal(plate) != null)
             {
-                Console.Error.WriteLine($"Error: {refusal} Use --autonest.");
+                Console.Error.WriteLine(OutlinedSheetMessage);
                 return 2;
             }
 

OpenNest.FrontEnd.Tests/McpPlateToolsTests.cs

@@ -37,6 +37,26 @@ public class McpPlateToolsTests : IDisposable
         Assert.Null(sessionOnly.GetPlate(1));
     }
 
+    [Fact]
+    public void FillOnOutlinedSheetNamesTheMcpToolsThatCanNestIt()
+    {
+        var session = new NestSession { Nest = new Nest("fixture") };
+        session.Nest.Drawings.Add(new Drawing("square", new Program()));
+        var outline = new SheetOutline(new[]
+        {
+            new Vector(0, 0), new Vector(96, 0), new Vector(96, 24),
+            new Vector(48, 24), new Vector(48, 48), new Vector(0, 48),
+        });
+        var plate = new Plate(10, 10) { Outline = outline };
+        session.Nest.Plates.Add(plate);
+
+        Assert.Equal(
+            "Error: Fill strategies need a rectangular sheet. Use autonest_plate or autonest_job "
+                + "with engine Irregular. Nothing committed.",
+            new NestingTools(session).FillPlate(0, "square"));
+        Assert.Empty(plate.Parts);
+    }
+
     private static string Delete(SetupTools tools, int index) => tools.DeletePlate(index);
 
     [Fact]

OpenNest.Mcp/Tools/NestingTools.cs

@@ -68,8 +68,8 @@ namespace OpenNest.Mcp.Tools
             var strategy = ResolveStrategy(engine);
             if (strategy == null)
                 return EngineError(engine);
-            if (PlateFillService.Refusal(plate) is { } refusal)
-                return $"Error: {refusal} Nothing committed.";
+            if (OutlinedSheetRefusal(plate) is { } refusal)
+                return refusal;
 
             var countBefore = plate.Parts.Count;
             var item = new NestItem { Drawing = drawing, Quantity = quantity };
@@ -125,8 +125,8 @@ namespace OpenNest.Mcp.Tools
             var strategy = ResolveStrategy(engine);
             if (strategy == null)
                 return EngineError(engine);
-            if (PlateFillService.Refusal(plate) is { } refusal)
-                return $"Error: {refusal} Nothing committed.";
+            if (OutlinedSheetRefusal(plate) is { } refusal)
+                return refusal;
 
             var countBefore = plate.Parts.Count;
             var item = new NestItem { Drawing = drawing, Quantity = quantity };
@@ -179,8 +179,8 @@ namespace OpenNest.Mcp.Tools
             var strategy = ResolveStrategy(engine);
             if (strategy == null)
                 return EngineError(engine);
-            if (PlateFillService.Refusal(plate) is { } refusal)
-                return $"Error: {refusal} Nothing committed.";
+            if (OutlinedSheetRefusal(plate) is { } refusal)
+                return refusal;
 
             var finder = RemnantFinder.FromPlate(plate);
             var remnants = finder.FindRemnants();
@@ -248,8 +248,8 @@ namespace OpenNest.Mcp.Tools
             var strategy = ResolveStrategy(engine);
             if (strategy == null)
                 return EngineError(engine);
-            if (PlateFillService.Refusal(plate) is { } refusal)
-                return $"Error: {refusal} Nothing committed.";
+            if (OutlinedSheetRefusal(plate) is { } refusal)
+                return refusal;
 
             var parsed = ParseItems(drawingNames, quantities);
             if (parsed.error != null)
@@ -614,6 +614,17 @@ namespace OpenNest.Mcp.Tools
         /// </summary>
         private static string ResolveStrategy(string engine) => EngineNameResolver.Classify(engine).FillStrategy;
 
+        internal const string OutlinedSheetMessage =
+            "Error: Fill strategies need a rectangular sheet. Use autonest_plate or autonest_job "
+            + "with engine Irregular. Nothing committed.";
+
+        /// <summary>
+        /// The fill tools' refusal for an outlined sheet, naming the MCP tools that can nest it;
+        /// null when the plate is rectangular.
+        /// </summary>
+        private static string OutlinedSheetRefusal(Plate plate) =>
+            PlateFillService.Refusal(plate) == null ? null : OutlinedSheetMessage;
+
         private static string EngineError(string engine)
         {
             var classified = EngineNameResolver.Classify(engine);