fix: Cincinnati post processor arc feedrate, G89 spacing, pallet exchange, and preamble

- Add radius-based arc feedrate calculation (Variables/Percentages modes)
  with configurable radius ranges (#123/#124/#125 or inline expressions)
- Fix arc distance in SpeedClassifier using actual arc length instead of
  chord length (full circles previously computed as zero)
- Fix G89 P spacing: P now adjacent to filename per CL-707 manual syntax
- Add lead-out feedrate support (#129) and arc lead-in feedrate (#127)
- Fix pallet exchange: StartAndEnd emits M50 in preamble + last sheet only
- Add G121 Smart Rapids emission when UseSmartRapids is enabled
- Add G90 absolute mode to main program preamble alongside G20/G21

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

OpenNest.Posts.Cincinnati/CincinnatiFeatureWriter.cs

@@ -70,7 +70,7 @@ public sealed class CincinnatiFeatureWriter
             {
                 var speedClass = _speedClassifier.Classify(ctx.CutDistance, ctx.SheetDiagonal);
                 var cutDist = _speedClassifier.FormatCutDist(ctx.CutDistance, ctx.SheetDiagonal);
-                writer.WriteLine($"G89 P {lib} ({speedClass} {cutDist})");
+                writer.WriteLine($"G89 P{lib} ({speedClass} {cutDist})");
             }
             else
             {
@@ -108,7 +108,7 @@ public sealed class CincinnatiFeatureWriter
                 sb.Append($"G1 X{_fmt.FormatCoord(linear.EndPoint.X)} Y{_fmt.FormatCoord(linear.EndPoint.Y)}");
 
                 // Feedrate — etch always uses process feedrate
-                var feedVar = ctx.IsEtch ? "#148" : GetFeedVariable(linear.Layer);
+                var feedVar = ctx.IsEtch ? "#148" : GetLinearFeedVariable(linear.Layer);
                 if (feedVar != lastFeedVar)
                 {
                     sb.Append($" F{feedVar}");
@@ -138,11 +138,11 @@ public sealed class CincinnatiFeatureWriter
                 var j = arc.CenterPoint.Y - currentPos.Y;
                 sb.Append($" I{_fmt.FormatCoord(i)} J{_fmt.FormatCoord(j)}");
 
-                // Feedrate — etch always uses process feedrate, cut uses layer-based
+                // Feedrate — etch always uses process feedrate, cut uses layer/radius-based
+                var radius = currentPos.DistanceTo(arc.CenterPoint);
                 var isFullCircle = IsFullCircle(currentPos, arc.EndPoint);
                 var feedVar = ctx.IsEtch ? "#148"
-                    : isFullCircle ? "[#148*#128]"
+                    : GetArcFeedrate(arc.Layer, radius, isFullCircle);
-                    : GetFeedVariable(arc.Layer);
                 if (feedVar != lastFeedVar)
                 {
                     sb.Append($" F{feedVar}");
@@ -223,16 +223,45 @@ public sealed class CincinnatiFeatureWriter
         }
     }
 
-    private static string GetFeedVariable(LayerType layer)
+    private static string GetLinearFeedVariable(LayerType layer)
     {
         return layer switch
         {
             LayerType.Leadin => "#126",
-            LayerType.Cut => "#148",
+            LayerType.Leadout => "#129",
             _ => "#148"
         };
     }
 
+    private string GetArcFeedrate(LayerType layer, double radius, bool isFullCircle)
+    {
+        if (layer == LayerType.Leadin) return "#127";
+        if (layer == LayerType.Leadout) return "#129";
+        if (isFullCircle) return "[#148*#128]";
+        return GetArcCutFeedrate(radius);
+    }
+
+    private string GetArcCutFeedrate(double radius)
+    {
+        if (_config.ArcFeedrate == ArcFeedrateMode.None)
+            return "#148";
+
+        // Find the smallest range that contains this radius
+        ArcFeedrateRange best = null;
+        foreach (var range in _config.ArcFeedrateRanges)
+        {
+            if (radius <= range.MaxRadius && (best == null || range.MaxRadius < best.MaxRadius))
+                best = range;
+        }
+
+        if (best == null)
+            return "#148";
+
+        return _config.ArcFeedrate == ArcFeedrateMode.Variables
+            ? $"#{best.VariableNumber}"
+            : $"[#148*{best.FeedratePercent.ToString("0.##", System.Globalization.CultureInfo.InvariantCulture)}]";
+    }
+
     private static bool IsFullCircle(Vector start, Vector end)
     {
         return Tolerance.IsEqualTo(start.X, end.X) && Tolerance.IsEqualTo(start.Y, end.Y);

OpenNest.Posts.Cincinnati/CincinnatiPostConfig.cs

@@ -269,12 +269,35 @@ namespace OpenNest.Posts.Cincinnati
         /// </summary>
         public double LeadInArcLine2FeedratePercent { get; set; } = 0.5;
 
+        /// <summary>
+        /// Gets or sets the feedrate percentage for lead-out moves.
+        /// Default: 0.5 (50%)
+        /// </summary>
+        public double LeadOutFeedratePercent { get; set; } = 0.5;
+
         /// <summary>
         /// Gets or sets the feedrate multiplier for circular cuts.
         /// Default: 0.8 (80%)
         /// </summary>
         public double CircleFeedrateMultiplier { get; set; } = 0.8;
 
+        /// <summary>
+        /// Gets or sets the arc feedrate calculation mode.
+        /// Default: ArcFeedrateMode.None
+        /// </summary>
+        public ArcFeedrateMode ArcFeedrate { get; set; } = ArcFeedrateMode.None;
+
+        /// <summary>
+        /// Gets or sets the radius-based arc feedrate ranges.
+        /// Ranges are matched from smallest MaxRadius to largest.
+        /// </summary>
+        public List<ArcFeedrateRange> ArcFeedrateRanges { get; set; } = new()
+        {
+            new() { MaxRadius = 0.125, FeedratePercent = 0.25, VariableNumber = 123 },
+            new() { MaxRadius = 0.750, FeedratePercent = 0.50, VariableNumber = 124 },
+            new() { MaxRadius = 4.500, FeedratePercent = 0.80, VariableNumber = 125 }
+        };
+
         /// <summary>
         /// Gets or sets the variable number for sheet width.
         /// Default: 110
@@ -301,4 +324,34 @@ namespace OpenNest.Posts.Cincinnati
         public string Gas { get; set; } = "";
         public string Library { get; set; } = "";
     }
+
+    /// <summary>
+    /// Specifies how arc feedrates are calculated based on radius.
+    /// </summary>
+    public enum ArcFeedrateMode
+    {
+        /// <summary>No radius-based arc feedrate adjustment (only full circles use multiplier).</summary>
+        None,
+
+        /// <summary>Inline percentage expressions: F [#148*pct] based on radius range.</summary>
+        Percentages,
+
+        /// <summary>Radius-range-based variables: F #varNum based on radius range.</summary>
+        Variables
+    }
+
+    /// <summary>
+    /// Defines a radius range and its associated feedrate for arc moves.
+    /// </summary>
+    public class ArcFeedrateRange
+    {
+        /// <summary>Maximum radius for this range (inclusive).</summary>
+        public double MaxRadius { get; set; }
+
+        /// <summary>Feedrate as a fraction of process feedrate (e.g. 0.25 = 25%).</summary>
+        public double FeedratePercent { get; set; }
+
+        /// <summary>Variable number for Variables mode (e.g. 123).</summary>
+        public int VariableNumber { get; set; }
+    }
 }

OpenNest.Posts.Cincinnati/CincinnatiPostProcessor.cs

@@ -112,8 +112,9 @@ namespace OpenNest.Posts.Cincinnati
                 var sheetIndex = i + 1;
                 var subNumber = Config.SheetSubprogramStart + i;
                 var cutLibrary = resolver.ResolveCutLibrary(plate.Material?.Name ?? "", plate.Thickness, gas);
+                var isLastSheet = i == plates.Count - 1;
                 sheetWriter.Write(writer, plate, nest.Name ?? "NEST", sheetIndex, subNumber,
-                    cutLibrary, etchLibrary, partSubprograms);
+                    cutLibrary, etchLibrary, partSubprograms, isLastSheet);
             }
 
             // Part sub-programs (if enabled)
@@ -148,6 +149,18 @@ namespace OpenNest.Posts.Cincinnati
             vars.GetOrCreate("LeadInFeedrate", 126, $"[#148*{Config.LeadInFeedratePercent}]");
             vars.GetOrCreate("LeadInArcLine2Feedrate", 127, $"[#148*{Config.LeadInArcLine2FeedratePercent}]");
             vars.GetOrCreate("CircleFeedrate", 128, Config.CircleFeedrateMultiplier.ToString("0.#"));
+            vars.GetOrCreate("LeadOutFeedrate", 129, $"[#148*{Config.LeadOutFeedratePercent}]");
+
+            if (Config.ArcFeedrate == ArcFeedrateMode.Variables)
+            {
+                foreach (var range in Config.ArcFeedrateRanges)
+                {
+                    var name = $"ArcFeedR{range.MaxRadius.ToString("0.###", System.Globalization.CultureInfo.InvariantCulture)}";
+                    vars.GetOrCreate(name, range.VariableNumber,
+                        $"[#148*{range.FeedratePercent.ToString("0.##", System.Globalization.CultureInfo.InvariantCulture)}]");
+                }
+            }
+
             return vars;
         }
     }

OpenNest.Posts.Cincinnati/CincinnatiPreambleWriter.cs

@@ -37,15 +37,21 @@ public sealed class CincinnatiPreambleWriter
 
         w.WriteLine(CoordinateFormatter.Comment("MAIN PROGRAM"));
 
-        w.WriteLine(_config.PostedUnits == Units.Millimeters ? "G21" : "G20");
+        w.WriteLine(_config.PostedUnits == Units.Millimeters ? "G21 G90" : "G20 G90");
+
+        if (_config.UseSmartRapids)
+            w.WriteLine("G121 (SMART RAPIDS)");
 
         w.WriteLine("M42");
 
         if (_config.ProcessParameterMode == G89Mode.LibraryFile && !string.IsNullOrEmpty(initialLibrary))
-            w.WriteLine($"G89 P {initialLibrary}");
+            w.WriteLine($"G89 P{initialLibrary}");
 
         w.WriteLine($"M98 P{_config.VariableDeclarationSubprogram} (Variable Declaration)");
 
+        if (_config.PalletExchange == PalletMode.StartAndEnd)
+            w.WriteLine("M50");
+
         w.WriteLine("GOTO1 (GOTO SHEET NUMBER)");
 
         for (var i = 1; i <= sheetCount; i++)

OpenNest.Posts.Cincinnati/CincinnatiSheetWriter.cs

@@ -37,7 +37,8 @@ public sealed class CincinnatiSheetWriter
     /// </param>
     public void Write(TextWriter w, Plate plate, string nestName, int sheetIndex, int subNumber,
         string cutLibrary, string etchLibrary,
-        Dictionary<(int, long), int> partSubprograms = null)
+        Dictionary<(int, long), int> partSubprograms = null,
+        bool isLastSheet = false)
     {
         if (plate.Parts.Count == 0)
             return;
@@ -64,12 +65,12 @@ public sealed class CincinnatiSheetWriter
         w.WriteLine("N10000");
         w.WriteLine("G92 X#5021 Y#5022");
         if (!string.IsNullOrEmpty(cutLibrary))
-            w.WriteLine($"G89 P {cutLibrary}");
+            w.WriteLine($"G89 P{cutLibrary}");
         w.WriteLine($"M98 P{varDeclSub} (Variable Declaration)");
         w.WriteLine("G90");
         w.WriteLine("M47");
         if (!string.IsNullOrEmpty(cutLibrary))
-            w.WriteLine($"G89 P {cutLibrary}");
+            w.WriteLine($"G89 P{cutLibrary}");
         w.WriteLine("GOTO1( Goto Feature )");
 
         // 3. Order parts: non-cutoff sorted by Bottom then Left, cutoffs last
@@ -94,7 +95,9 @@ public sealed class CincinnatiSheetWriter
         // 5. Footer
         w.WriteLine("M42");
         w.WriteLine("G0 X0 Y0");
-        if (_config.PalletExchange != PalletMode.None)
+        var emitM50 = _config.PalletExchange == PalletMode.EndOfSheet
+            || (_config.PalletExchange == PalletMode.StartAndEnd && isLastSheet);
+        if (emitM50)
             w.WriteLine($"N{sheetIndex + 1} M50");
         w.WriteLine($"M99 (END OF {nestName}.{sheetIndex:D3})");
     }

OpenNest.Posts.Cincinnati/FeatureUtils.cs

@@ -1,6 +1,7 @@
 using System.Collections.Generic;
 using OpenNest.CNC;
 using OpenNest.Geometry;
+using OpenNest.Math;
 
 namespace OpenNest.Posts.Cincinnati;
 
@@ -105,11 +106,48 @@ public static class FeatureUtils
             }
             else if (code is ArcMove arc)
             {
-                distance += currentPos.DistanceTo(arc.EndPoint);
+                distance += ComputeArcLength(currentPos, arc);
                 currentPos = arc.EndPoint;
             }
         }
 
         return distance;
     }
+
+    /// <summary>
+    /// Computes the arc length from the current position through an arc move.
+    /// Uses radius * sweep angle instead of chord length.
+    /// </summary>
+    public static double ComputeArcLength(Vector startPos, ArcMove arc)
+    {
+        var radius = startPos.DistanceTo(arc.CenterPoint);
+        if (radius < Tolerance.Epsilon)
+            return 0.0;
+
+        // Full circle: start ≈ end
+        if (Tolerance.IsEqualTo(startPos.X, arc.EndPoint.X)
+            && Tolerance.IsEqualTo(startPos.Y, arc.EndPoint.Y))
+            return 2.0 * System.Math.PI * radius;
+
+        var startAngle = System.Math.Atan2(
+            startPos.Y - arc.CenterPoint.Y,
+            startPos.X - arc.CenterPoint.X);
+        var endAngle = System.Math.Atan2(
+            arc.EndPoint.Y - arc.CenterPoint.Y,
+            arc.EndPoint.X - arc.CenterPoint.X);
+
+        double sweep;
+        if (arc.Rotation == RotationType.CW)
+        {
+            sweep = startAngle - endAngle;
+            if (sweep <= 0) sweep += 2.0 * System.Math.PI;
+        }
+        else
+        {
+            sweep = endAngle - startAngle;
+            if (sweep <= 0) sweep += 2.0 * System.Math.PI;
+        }
+
+        return radius * sweep;
+    }
 }

OpenNest.Tests/Cincinnati/CincinnatiFeatureWriterTests.cs

@@ -297,7 +297,7 @@ public class CincinnatiFeatureWriterTests
         ctx.SheetDiagonal = 30.0;
         var output = WriteFeature(config, ctx);
 
-        Assert.Contains("G89 P MILD10", output);
+        Assert.Contains("G89 PMILD10", output);
     }
 
     [Fact]
@@ -470,6 +470,123 @@ public class CincinnatiFeatureWriterTests
         Assert.True(m131Idx < m47Idx, "M131 should come before M47");
     }
 
+    [Fact]
+    public void LeadoutFeedrate_UsesVariable129()
+    {
+        var config = DefaultConfig();
+        config.KerfCompensation = KerfMode.PreApplied;
+        var codes = new List<ICode>
+        {
+            new RapidMove(1.0, 1.0),
+            new LinearMove(2.0, 1.0) { Layer = LayerType.Leadout }
+        };
+        var ctx = SimpleContext(codes);
+        var output = WriteFeature(config, ctx);
+
+        Assert.Contains("F#129", output);
+    }
+
+    [Fact]
+    public void ArcLeadin_UsesVariable127()
+    {
+        var config = DefaultConfig();
+        config.KerfCompensation = KerfMode.PreApplied;
+        var codes = new List<ICode>
+        {
+            new RapidMove(10.0, 20.0),
+            new ArcMove(new Vector(12.0, 20.0), new Vector(11.0, 20.0), RotationType.CCW) { Layer = LayerType.Leadin }
+        };
+        var ctx = SimpleContext(codes);
+        var output = WriteFeature(config, ctx);
+
+        Assert.Contains("F#127", output);
+    }
+
+    [Fact]
+    public void ArcFeedrate_VariablesMode_UsesRadiusRangeVariable()
+    {
+        var config = DefaultConfig();
+        config.KerfCompensation = KerfMode.PreApplied;
+        config.ArcFeedrate = ArcFeedrateMode.Variables;
+        // Arc with radius 0.5 (center at 10.5, 20; start at 10, 20) → R=0.5 → #124 (R ≤ 0.750)
+        var codes = new List<ICode>
+        {
+            new RapidMove(10.0, 20.0),
+            new ArcMove(new Vector(11.0, 20.0), new Vector(10.5, 20.0), RotationType.CW) { Layer = LayerType.Cut }
+        };
+        var ctx = SimpleContext(codes);
+        var output = WriteFeature(config, ctx);
+
+        Assert.Contains("F#124", output);
+    }
+
+    [Fact]
+    public void ArcFeedrate_PercentagesMode_UsesInlineExpression()
+    {
+        var config = DefaultConfig();
+        config.KerfCompensation = KerfMode.PreApplied;
+        config.ArcFeedrate = ArcFeedrateMode.Percentages;
+        // Arc with radius 0.1 (≤ 0.125) → 25%
+        var codes = new List<ICode>
+        {
+            new RapidMove(10.0, 20.0),
+            new ArcMove(new Vector(10.2, 20.0), new Vector(10.1, 20.0), RotationType.CW) { Layer = LayerType.Cut }
+        };
+        var ctx = SimpleContext(codes);
+        var output = WriteFeature(config, ctx);
+
+        Assert.Contains("F[#148*0.25]", output);
+    }
+
+    [Fact]
+    public void ArcFeedrate_LargeRadius_UsesProcessFeedrate()
+    {
+        var config = DefaultConfig();
+        config.KerfCompensation = KerfMode.PreApplied;
+        config.ArcFeedrate = ArcFeedrateMode.Variables;
+        // Arc with radius 10 (> 4.500) → falls through to #148
+        var codes = new List<ICode>
+        {
+            new RapidMove(0.0, 0.0),
+            new ArcMove(new Vector(20.0, 0.0), new Vector(10.0, 0.0), RotationType.CCW) { Layer = LayerType.Cut }
+        };
+        var ctx = SimpleContext(codes);
+        var output = WriteFeature(config, ctx);
+
+        Assert.Contains("F#148", output);
+    }
+
+    [Fact]
+    public void ArcFeedrate_NoneMode_UsesProcessFeedrateForNonCircle()
+    {
+        var config = DefaultConfig();
+        config.KerfCompensation = KerfMode.PreApplied;
+        config.ArcFeedrate = ArcFeedrateMode.None;
+        // Small radius arc but mode is None → process feedrate
+        var codes = new List<ICode>
+        {
+            new RapidMove(10.0, 20.0),
+            new ArcMove(new Vector(10.2, 20.0), new Vector(10.1, 20.0), RotationType.CW) { Layer = LayerType.Cut }
+        };
+        var ctx = SimpleContext(codes);
+        var output = WriteFeature(config, ctx);
+
+        Assert.Contains("F#148", output);
+    }
+
+    [Fact]
+    public void G89_PAdjacentToFilename()
+    {
+        var config = DefaultConfig();
+        var ctx = SimpleContext();
+        ctx.LibraryFile = "MS135N2.lib";
+        var output = WriteFeature(config, ctx);
+
+        // P must be directly adjacent to filename, no space
+        Assert.Contains("G89 PMS135N2.lib", output);
+        Assert.DoesNotContain("G89 P MS135N2.lib", output);
+    }
+
     private static int CountOccurrences(string text, string pattern)
     {
         var count = 0;

OpenNest.Tests/Cincinnati/CincinnatiPostProcessorTests.cs

@@ -43,6 +43,74 @@ public class CincinnatiPostProcessorTests
         Assert.Contains("M99", output);
     }
 
+    [Fact]
+    public void Post_EmitsLeadOutVariable()
+    {
+        var nest = CreateTestNest();
+        var config = new CincinnatiPostConfig { PostedAccuracy = 4 };
+        var post = new CincinnatiPostProcessor(config);
+
+        using var ms = new MemoryStream();
+        post.Post(nest, ms);
+
+        var output = Encoding.UTF8.GetString(ms.ToArray());
+        Assert.Contains("#129=", output);
+    }
+
+    [Fact]
+    public void Post_WithArcFeedrateVariables_EmitsRangeVariables()
+    {
+        var nest = CreateTestNest();
+        var config = new CincinnatiPostConfig
+        {
+            PostedAccuracy = 4,
+            ArcFeedrate = ArcFeedrateMode.Variables
+        };
+        var post = new CincinnatiPostProcessor(config);
+
+        using var ms = new MemoryStream();
+        post.Post(nest, ms);
+
+        var output = Encoding.UTF8.GetString(ms.ToArray());
+        Assert.Contains("#123=", output);
+        Assert.Contains("#124=", output);
+        Assert.Contains("#125=", output);
+    }
+
+    [Fact]
+    public void Post_WithArcFeedrateNone_OmitsRangeVariables()
+    {
+        var nest = CreateTestNest();
+        var config = new CincinnatiPostConfig
+        {
+            PostedAccuracy = 4,
+            ArcFeedrate = ArcFeedrateMode.None
+        };
+        var post = new CincinnatiPostProcessor(config);
+
+        using var ms = new MemoryStream();
+        post.Post(nest, ms);
+
+        var output = Encoding.UTF8.GetString(ms.ToArray());
+        Assert.DoesNotContain("#123=", output);
+        Assert.DoesNotContain("#124=", output);
+        Assert.DoesNotContain("#125=", output);
+    }
+
+    [Fact]
+    public void Post_EmitsG90InPreamble()
+    {
+        var nest = CreateTestNest();
+        var config = new CincinnatiPostConfig { PostedAccuracy = 4 };
+        var post = new CincinnatiPostProcessor(config);
+
+        using var ms = new MemoryStream();
+        post.Post(nest, ms);
+
+        var output = Encoding.UTF8.GetString(ms.ToArray());
+        Assert.Contains("G20 G90", output);
+    }
+
     [Fact]
     public void Post_ImplementsIPostProcessor()
     {

OpenNest.Tests/Cincinnati/CincinnatiPreambleWriterTests.cs

@@ -24,9 +24,9 @@ public class CincinnatiPreambleWriterTests
         var output = sb.ToString();
         Assert.Contains("( NEST TestNest )", output);
         Assert.Contains("( CONFIGURATION - CL940 )", output);
-        Assert.Contains("G20", output);
+        Assert.Contains("G20 G90", output);
         Assert.Contains("M42", output);
-        Assert.Contains("G89 P MS135N2PANEL.lib", output);
+        Assert.Contains("G89 PMS135N2PANEL.lib", output);
         Assert.Contains("M98 P100 (Variable Declaration)", output);
         Assert.Contains("GOTO1 (GOTO SHEET NUMBER)", output);
         Assert.Contains("N1 M98 P101 (SHEET 1)", output);
@@ -44,7 +44,72 @@ public class CincinnatiPreambleWriterTests
 
         writer.WriteMainProgram(sw, "Test", "", 1, "");
 
-        Assert.Contains("G21", sb.ToString());
+        Assert.Contains("G21 G90", sb.ToString());
+    }
+
+    [Fact]
+    public void WriteMainProgram_EmitsG90WithUnits()
+    {
+        var config = new CincinnatiPostConfig { PostedUnits = Units.Inches };
+        var sb = new StringBuilder();
+        using var sw = new StringWriter(sb);
+        var writer = new CincinnatiPreambleWriter(config);
+
+        writer.WriteMainProgram(sw, "Test", "", 1, "");
+
+        Assert.Contains("G20 G90", sb.ToString());
+    }
+
+    [Fact]
+    public void WriteMainProgram_EmitsG121_WhenSmartRapidsEnabled()
+    {
+        var config = new CincinnatiPostConfig { UseSmartRapids = true };
+        var sb = new StringBuilder();
+        using var sw = new StringWriter(sb);
+        var writer = new CincinnatiPreambleWriter(config);
+
+        writer.WriteMainProgram(sw, "Test", "", 1, "");
+
+        Assert.Contains("G121 (SMART RAPIDS)", sb.ToString());
+    }
+
+    [Fact]
+    public void WriteMainProgram_OmitsG121_WhenSmartRapidsDisabled()
+    {
+        var config = new CincinnatiPostConfig { UseSmartRapids = false };
+        var sb = new StringBuilder();
+        using var sw = new StringWriter(sb);
+        var writer = new CincinnatiPreambleWriter(config);
+
+        writer.WriteMainProgram(sw, "Test", "", 1, "");
+
+        Assert.DoesNotContain("G121", sb.ToString());
+    }
+
+    [Fact]
+    public void WriteMainProgram_EmitsM50_WhenStartAndEnd()
+    {
+        var config = new CincinnatiPostConfig { PalletExchange = PalletMode.StartAndEnd };
+        var sb = new StringBuilder();
+        using var sw = new StringWriter(sb);
+        var writer = new CincinnatiPreambleWriter(config);
+
+        writer.WriteMainProgram(sw, "Test", "", 1, "");
+
+        Assert.Contains("M50", sb.ToString());
+    }
+
+    [Fact]
+    public void WriteMainProgram_OmitsM50_WhenEndOfSheet()
+    {
+        var config = new CincinnatiPostConfig { PalletExchange = PalletMode.EndOfSheet };
+        var sb = new StringBuilder();
+        using var sw = new StringWriter(sb);
+        var writer = new CincinnatiPreambleWriter(config);
+
+        writer.WriteMainProgram(sw, "Test", "", 1, "");
+
+        Assert.DoesNotContain("M50", sb.ToString());
     }
 
     [Fact]

OpenNest.Tests/Cincinnati/CincinnatiSheetWriterTests.cs

@@ -32,7 +32,7 @@ public class CincinnatiSheetWriterTests
         Assert.Contains("#110=", output);
         Assert.Contains("#111=", output);
         Assert.Contains("G92 X#5021 Y#5022", output);
-        Assert.Contains("G89 P MS135N2PANEL.lib", output);
+        Assert.Contains("G89 PMS135N2PANEL.lib", output);
         Assert.Contains("M99", output);
     }
 
@@ -137,9 +137,110 @@ public class CincinnatiSheetWriterTests
         Assert.True(g85Idx < g84Idx, "G85 (etch) should come before G84 (cut)");
 
         // Etch uses etch library
-        Assert.Contains("G89 P EtchN2.lib", output);
+        Assert.Contains("G89 PEtchN2.lib", output);
         // Cut uses cut library
-        Assert.Contains("G89 P MS250O2.lib", output);
+        Assert.Contains("G89 PMS250O2.lib", output);
+    }
+
+    [Fact]
+    public void WriteSheet_StartAndEnd_NoM50OnNonLastSheet()
+    {
+        var config = new CincinnatiPostConfig
+        {
+            PalletExchange = PalletMode.StartAndEnd,
+            PostedAccuracy = 4
+        };
+        var plate = new Plate(48.0, 96.0);
+        plate.Parts.Add(new Part(new Drawing("TestPart", CreateSimpleProgram())));
+
+        var sb = new StringBuilder();
+        using var sw = new StringWriter(sb);
+        var sheetWriter = new CincinnatiSheetWriter(config, new ProgramVariableManager());
+
+        sheetWriter.Write(sw, plate, "TestNest", 1, 101, "", "", isLastSheet: false);
+
+        var output = sb.ToString();
+        Assert.DoesNotContain("M50", output);
+    }
+
+    [Fact]
+    public void WriteSheet_StartAndEnd_M50OnLastSheet()
+    {
+        var config = new CincinnatiPostConfig
+        {
+            PalletExchange = PalletMode.StartAndEnd,
+            PostedAccuracy = 4
+        };
+        var plate = new Plate(48.0, 96.0);
+        plate.Parts.Add(new Part(new Drawing("TestPart", CreateSimpleProgram())));
+
+        var sb = new StringBuilder();
+        using var sw = new StringWriter(sb);
+        var sheetWriter = new CincinnatiSheetWriter(config, new ProgramVariableManager());
+
+        sheetWriter.Write(sw, plate, "TestNest", 1, 101, "", "", isLastSheet: true);
+
+        var output = sb.ToString();
+        Assert.Contains("M50", output);
+    }
+
+    [Fact]
+    public void WriteSheet_EndOfSheet_AlwaysEmitsM50()
+    {
+        var config = new CincinnatiPostConfig
+        {
+            PalletExchange = PalletMode.EndOfSheet,
+            PostedAccuracy = 4
+        };
+        var plate = new Plate(48.0, 96.0);
+        plate.Parts.Add(new Part(new Drawing("TestPart", CreateSimpleProgram())));
+
+        var sb = new StringBuilder();
+        using var sw = new StringWriter(sb);
+        var sheetWriter = new CincinnatiSheetWriter(config, new ProgramVariableManager());
+
+        sheetWriter.Write(sw, plate, "TestNest", 1, 101, "", "", isLastSheet: false);
+
+        var output = sb.ToString();
+        Assert.Contains("M50", output);
+    }
+
+    [Fact]
+    public void ComputeArcLength_FullCircle_Returns2PiR()
+    {
+        var start = new Vector(10.0, 20.0);
+        var arc = new ArcMove(new Vector(10.0, 20.0), new Vector(15.0, 20.0), RotationType.CW);
+        var length = FeatureUtils.ComputeArcLength(start, arc);
+
+        // Radius = 5, full circle = 2 * PI * 5 ≈ 31.416
+        Assert.Equal(2.0 * System.Math.PI * 5.0, length, 4);
+    }
+
+    [Fact]
+    public void ComputeArcLength_Semicircle_ReturnsPiR()
+    {
+        // Semicircle from (0,0) to (10,0) with center at (5,0), CCW → goes through (5,5)
+        var start = new Vector(0.0, 0.0);
+        var arc = new ArcMove(new Vector(10.0, 0.0), new Vector(5.0, 0.0), RotationType.CCW);
+        var length = FeatureUtils.ComputeArcLength(start, arc);
+
+        // Radius = 5, semicircle = PI * 5 ≈ 15.708
+        Assert.Equal(System.Math.PI * 5.0, length, 4);
+    }
+
+    [Fact]
+    public void ComputeCutDistance_WithArcs_UsesArcLengthNotChord()
+    {
+        // Full circle: chord = 0 but arc length = 2πr
+        var codes = new List<ICode>
+        {
+            new RapidMove(10.0, 20.0),
+            new ArcMove(new Vector(10.0, 20.0), new Vector(15.0, 20.0), RotationType.CW) { Layer = LayerType.Cut }
+        };
+        var distance = FeatureUtils.ComputeCutDistance(codes);
+
+        // Full circle with R=5 → 2πr ≈ 31.416
+        Assert.True(distance > 30.0, $"Expected arc length > 30 but got {distance}");
     }
 
     [Fact]