feat(posting): require verification and explicit risk acknowledgment

OpenNest.Console/Program.cs

@@ -7,6 +7,7 @@ using System.Linq;
 using System.Reflection;
 using System.Threading;
 using OpenNest;
+using OpenNest.Diagnostics;
 using OpenNest.Engine;
 using OpenNest.Engine.Jobs;
 using OpenNest.Engine.Jobs.Adapters;
@@ -120,8 +121,8 @@ static class NestConsole
         var overlapCount = CheckOverlaps(plate, options);
 
         PrintResults(success, plate, elapsed);
-        Save(nest, options);
-        PostProcess(nest, options);
+        if (!SaveAndPost(nest, options))
+            return 1;
 
         return options.CheckOverlaps && overlapCount > 0 ? 1 : 0;
     }
@@ -194,6 +195,9 @@ static class NestConsole
                 case "--post" when i + 1 < args.Length:
                     o.PostName = args[++i];
                     break;
+                case "--acknowledge-post-risks":
+                    o.AcknowledgePostRisks = true;
+                    break;
                 case "--post-output" when i + 1 < args.Length:
                     o.PostOutput = args[++i];
                     break;
@@ -557,18 +561,16 @@ static class NestConsole
         if (options.NoSave)
             return;
 
-        var firstInput = options.InputFiles[0];
-        var outputFile =
-            options.OutputFile
-            ?? Path.Combine(
-                Path.GetDirectoryName(firstInput),
-                $"{Path.GetFileNameWithoutExtension(firstInput)}-result{NestFormat.FileExtension}"
-            );
+        var outputFile = NestOutputPath(options);
 
         new NestWriter(nest).Write(outputFile);
         Console.WriteLine($"Saved: {outputFile}");
     }
 
+    static string NestOutputPath(Options options) => options.OutputFile
+        ?? Path.Combine(Path.GetDirectoryName(options.InputFiles[0]),
+            $"{Path.GetFileNameWithoutExtension(options.InputFiles[0])}-result{NestFormat.FileExtension}");
+
     static string ResolvePostsDir(Options options)
     {
         if (options.PostsDir != null)
@@ -633,10 +635,13 @@ static class NestConsole
             Console.WriteLine($"  {p.Name,-30} {p.Description}");
     }
 
-    static void PostProcess(Nest nest, Options options)
+    static bool SaveAndPost(Nest nest, Options options)
     {
         if (options.PostName == null)
-            return;
+        {
+            Save(nest, options);
+            return true;
+        }
 
         var postsDir = ResolvePostsDir(options);
         var processors = LoadPostProcessors(postsDir);
@@ -655,7 +660,15 @@ static class NestConsole
             else
                 Console.Error.WriteLine($"No post processors found in: {postsDir}");
 
-            return;
+            return false;
+        }
+
+        var verification = PostVerificationAnalyzer.AnalyzeForPost(nest, post);
+        Console.WriteLine(verification.ToDisplayText());
+        if (!verification.CanPost(options.AcknowledgePostRisks))
+        {
+            Console.Error.WriteLine("Posting blocked: review these warnings. To accept the risks, including possible head crashes and machine or material damage, explicitly use --acknowledge-post-risks for this invocation.");
+            return false;
         }
 
         var outputFile = options.PostOutput;
@@ -673,9 +686,18 @@ static class NestConsole
             ? multiFile.GetOutputFiles(nest, outputFile)
             : new[] { outputFile };
 
+        if (!options.NoSave && outputFiles.Any(file => string.Equals(
+            Path.GetFullPath(file), Path.GetFullPath(NestOutputPath(options)), StringComparison.OrdinalIgnoreCase)))
+        {
+            Console.Error.WriteLine("Error: nest save and CNC output paths must be different. No output was written.");
+            return false;
+        }
+
+        Save(nest, options);
         post.Post(nest, outputFile);
         foreach (var file in outputFiles)
             Console.WriteLine($"Post: {post.Name} -> {file}");
+        return true;
     }
 
     static void PrintUsage()
@@ -710,6 +732,7 @@ static class NestConsole
               --no-save              Skip saving output file
               --post <name>          Run a post processor after nesting
               --post-output <path>   Output file for post processor (default: <input>.cnc)
+              --acknowledge-post-risks  Explicitly accept displayed verification risks for this invocation
               --posts-dir <path>     Directory containing post processor DLLs (default: Posts/)
               --list-posts           List available post processors and exit
               -h, --help             Show this help
@@ -733,6 +756,7 @@ static class NestConsole
         public string Engine = "Default";
         public string TemplateFile;
         public string PostName;
+        public bool AcknowledgePostRisks;
         public string PostOutput;
         public string PostsDir;
         public bool ListPosts;

OpenNest.Core/Diagnostics/PostVerificationAnalyzer.cs

@@ -0,0 +1,290 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using OpenNest.CNC;
+using OpenNest.Geometry;
+
+namespace OpenNest.Diagnostics;
+
+/// <summary>
+/// Read-only pre-post diagnostics. The caller must keep the nest stable for the entire call.
+/// Placed programs are already rotated; only their placement translation is applied here.
+/// This intentionally does not invoke a post or promise machine collision avoidance.
+/// </summary>
+public static class PostVerificationAnalyzer
+{
+    public static PostVerificationReport AnalyzeForPost(Nest nest, IPostProcessor postProcessor,
+        CancellationToken cancellationToken = default)
+    {
+        var report = Analyze(nest, cancellationToken);
+        if (postProcessor is IPostVerificationSupport { PreservesPlacedProgramOrder: true })
+            return report;
+        var findings = report.Findings.ToList();
+        findings.Add(new(PostVerificationKind.Incomplete, 0, null, null,
+            $"Post '{postProcessor?.Name ?? "unknown"}' does not declare that it preserves placed part/contour order " +
+            "and pierce positions. Nest-level checks ran, but the final rapid sequence requires manual review."));
+        return new PostVerificationReport(findings);
+    }
+
+    public static PostVerificationReport Analyze(Nest nest, CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(nest);
+        cancellationToken.ThrowIfCancellationRequested();
+        var findings = new List<PostVerificationFinding>();
+        if (nest.Plates == null)
+        {
+            findings.Add(new(PostVerificationKind.Incomplete, 1, null, null, "Nest has no plate collection."));
+            return new PostVerificationReport(findings);
+        }
+        for (var plateIndex = 0; plateIndex < nest.Plates.Count; plateIndex++)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            var plate = nest.Plates[plateIndex];
+            var plateNumber = plateIndex + 1;
+            if (plate?.Parts == null)
+            {
+                findings.Add(new(PostVerificationKind.Incomplete, plateNumber, null, null,
+                    "Plate has no part collection."));
+                continue;
+            }
+            var materialParts = new List<Part>();
+            var indices = new List<int>();
+            var obstacles = new List<Obstacle>();
+            Vector? position = Vector.Zero;
+            for (var index = 0; index < plate.Parts.Count; index++)
+            {
+                cancellationToken.ThrowIfCancellationRequested();
+                var part = plate.Parts[index];
+                var partNumber = index + 1;
+                var cutoff = part?.BaseDrawing?.IsCutOff == true;
+                var expectsCuts = cutoff;
+                // Preflight even clean programs before calling the overlap converter: malformed
+                // recursive graphs must never reach Program.Clone or unguarded conversion.
+                if (!cutoff)
+                {
+                    try
+                    {
+                        var clean = Read(part?.BaseDrawing?.Program, Vector.Zero, null, cancellationToken);
+                        expectsCuts = clean.Any(move => !move.Rapid && move.Layer != LayerType.Scribe);
+                        if (!clean.Any(move => move.Layer == LayerType.Scribe)
+                            || expectsCuts)
+                        {
+                            materialParts.Add(part);
+                            indices.Add(partNumber);
+                        }
+                    }
+                    catch (Exception exception) when (IsInvalid(exception))
+                    {
+                        Incomplete("Overlap check: " + exception.Message);
+                    }
+                }
+                try
+                {
+                    if (part == null || !double.IsFinite(part.Rotation))
+                        throw new ArgumentException("Missing part or invalid rotation.");
+                    var moves = Read(part.Program, part.Location, position, cancellationToken);
+                    if (expectsCuts && !moves.Any(move => !move.Rapid
+                        && move.Layer is LayerType.Cut or LayerType.Display
+                        && move.Curve.Length > PostVerificationGeometry.Epsilon))
+                        Incomplete("Placed program has no cutting contour motions for this drawing.");
+                    AnalyzeMoves(moves, cutoff, obstacles, findings, plateNumber, partNumber, cancellationToken);
+                    position = moves[^1].End;
+                }
+                catch (Exception exception) when (IsInvalid(exception))
+                {
+                    Incomplete("Lead-in/rapid check: " + exception.Message);
+                    // Subsequent internal moves can still be checked, but the incoming segment
+                    // cannot be reconstructed after an invalid program.
+                    position = null;
+                }
+
+                void Incomplete(string message) => findings.Add(new(PostVerificationKind.Incomplete,
+                    plateNumber, partNumber, null, message));
+            }
+            cancellationToken.ThrowIfCancellationRequested();
+            var overlap = PlateOverlapAnalyzer.Analyze(
+                PlateOverlapAnalyzer.Capture(materialParts, cancellationToken), cancellationToken);
+            foreach (var pair in overlap.Pairs)
+                findings.Add(new(PostVerificationKind.Overlap, plateNumber, indices[pair.PartAId],
+                    indices[pair.PartBId], "Clean drawing material overlaps (holes subtracted)."));
+            foreach (var issue in overlap.Issues)
+                findings.Add(new(PostVerificationKind.Incomplete, plateNumber, indices[issue.PartAId],
+                    issue.PartBId is { } other ? indices[other] : null, "Overlap check: " + issue.Message));
+        }
+        cancellationToken.ThrowIfCancellationRequested();
+        return new PostVerificationReport(findings);
+    }
+
+    private static bool IsInvalid(Exception exception) => exception is
+        ArgumentException or InvalidOperationException or NotSupportedException or ArithmeticException;
+
+    private static List<Move> Read(Program program, Vector origin, Vector? previous,
+        CancellationToken token)
+    {
+        var moves = new List<Move>();
+        var visiting = new HashSet<Program>(ReferenceEqualityComparer.Instance);
+        var budget = 1000000;
+        Walk(program, origin, previous);
+        return moves;
+
+        Vector Walk(Program current, Vector frame, Vector? arrival)
+        {
+            token.ThrowIfCancellationRequested();
+            PostVerificationGeometry.Validate(frame);
+            if (current?.Codes == null || !visiting.Add(current) || visiting.Count > 64)
+                throw new ArgumentException("Missing, recursive or excessively nested program.");
+            var pos = frame;
+            var first = true;
+            var countBefore = moves.Count;
+            foreach (var code in current.Codes)
+            {
+                token.ThrowIfCancellationRequested();
+                if (--budget < 0)
+                    throw new ArgumentException("Program expansion exceeds the verification limit.");
+                if (code == null)
+                    throw new ArgumentException("Program contains a missing instruction.");
+                if (code is SubProgramCall call)
+                {
+                    if (!double.IsFinite(call.Rotation))
+                        throw new ArgumentException("Subprogram rotation is not finite.");
+                    // Call rotation is baked into the shared program by its setter. Do not
+                    // rotate again; offsets are frame-relative even in incremental mode.
+                    pos = Walk(call.Program, frame + call.Offset, first ? arrival : pos);
+                    first = false;
+                    continue;
+                }
+                if (code is not Motion motion)
+                {
+                    if (code is not (Comment or Feedrate or Kerf))
+                        throw new NotSupportedException("Unsupported program instruction.");
+                    continue;
+                }
+                // Posts disagree about incremental position after suppressed instructions.
+                // Never silently certify a trajectory whose semantics are ambiguous.
+                if (motion.Suppressed)
+                    throw new NotSupportedException("Suppressed motion requires post-specific verification.");
+                if (motion is not (RapidMove or LinearMove or ArcMove))
+                    throw new NotSupportedException("Unsupported motion.");
+                var reference = current.Mode == Mode.Incremental ? pos : frame;
+                var end = reference + motion.EndPoint;
+                PostVerificationGeometry.Validate(end);
+                var rapid = motion is RapidMove;
+                if (first && !rapid)
+                    moves.Add(new(arrival, frame, true, LayerType.Display, null));
+                var start = first && rapid ? arrival : pos;
+                var layer = motion switch
+                {
+                    LinearMove line => line.Layer,
+                    ArcMove arc => arc.Layer,
+                    _ => LayerType.Display
+                };
+                if (!Enum.IsDefined(layer))
+                    throw new NotSupportedException("Unsupported motion layer.");
+                if (motion is ArcMove direction && !Enum.IsDefined(direction.Rotation))
+                    throw new NotSupportedException("Unsupported arc direction.");
+                var curve = rapid ? null : PostVerificationGeometry.Curve.Create(pos, end,
+                    motion is ArcMove arcMove ? reference + arcMove.CenterPoint : null,
+                    motion is ArcMove { Rotation: RotationType.CW });
+                moves.Add(new(start, end, rapid, layer, curve));
+                pos = end;
+                first = false;
+            }
+            visiting.Remove(current);
+            if (moves.Count == countBefore)
+                throw new ArgumentException("Program has no motions.");
+            return pos;
+        }
+    }
+
+    private static void AnalyzeMoves(List<Move> moves, bool cutoff, List<Obstacle> obstacles,
+        List<PostVerificationFinding> findings, int plate, int part, CancellationToken token)
+    {
+        var contour = new List<PostVerificationGeometry.Curve>();
+        var unfinished = new List<PostVerificationGeometry.Curve[]>();
+        var hasLead = false;
+        var contourNumber = 0;
+        foreach (var move in moves)
+        {
+            token.ThrowIfCancellationRequested();
+            if (move.Rapid)
+            {
+                Finish();
+                hasLead = false;
+                if (move.Start is not { } start || start.DistanceTo(move.End) <= PostVerificationGeometry.Epsilon)
+                    continue;
+                foreach (var obstacle in obstacles)
+                {
+                    token.ThrowIfCancellationRequested();
+                    if (PostVerificationGeometry.Crosses(start, move.End, obstacle.Curves, token))
+                        findings.Add(new(PostVerificationKind.RapidCrossing, plate, part, obstacle.Part,
+                            $"Direct XY rapid crosses or touches completed untabbed contour {obstacle.Contour} " +
+                            $"of part {obstacle.Part}."));
+                }
+            }
+            else if (move.Layer == LayerType.Leadin)
+            {
+                Finish();
+                hasLead |= move.Curve.Length > PostVerificationGeometry.Epsilon;
+            }
+            else if (move.Layer is LayerType.Leadout or LayerType.Scribe)
+            {
+                if (move.Layer == LayerType.Leadout && contour.Count > 0
+                    && !PostVerificationGeometry.Closed(contour)
+                    && move.Curve.Length > PostVerificationGeometry.Epsilon)
+                    findings.Add(new(PostVerificationKind.Incomplete, plate, part, null,
+                        "A lead-out follows an open cutting contour and may cut through its retention gap. " +
+                        "Rapid safety for that contour requires manual review."));
+                Finish();
+                hasLead = false;
+            }
+            else if (move.Curve.Length > PostVerificationGeometry.Epsilon)
+            {
+                if (contour.Count == 0)
+                {
+                    contourNumber++;
+                    if (!cutoff && !hasLead)
+                        findings.Add(new(PostVerificationKind.MissingLeadIn, plate, part, null,
+                            $"Cutting contour {contourNumber} has no nonzero placed lead-in motion."));
+                    hasLead = false;
+                    // A rapid can pause/reposition without leaving any material gap.
+                    // Retain already-cut fragments, but do not turn them into obstacles
+                    // until an actually continuous chain closes.
+                    var previous = unfinished.FindIndex(chain =>
+                        chain[^1].End.DistanceTo(move.Curve.Start) <= PostVerificationGeometry.Epsilon);
+                    if (previous >= 0)
+                    {
+                        contour.AddRange(unfinished[previous]);
+                        unfinished.RemoveAt(previous);
+                    }
+                }
+                contour.Add(move.Curve);
+                // A completed contour becomes an obstacle immediately, not at part end.
+                if (PostVerificationGeometry.Closed(contour))
+                    Finish();
+            }
+        }
+        Finish();
+        if (unfinished.Count > 1)
+            findings.Add(new(PostVerificationKind.Incomplete, plate, part, null,
+                "Multiple interrupted/open cutting fragments remain. Their combined cuts may release material; " +
+                "they cannot be assumed to be retained by tabs. Review rapid travel manually."));
+
+        void Finish()
+        {
+            if (contour.Count == 0)
+                return;
+            // A real uncut gap leaves the contour attached. CuttingParameters can be stale;
+            // no flag or tab configuration is used as evidence of retention.
+            if (!cutoff && PostVerificationGeometry.Closed(contour))
+                obstacles.Add(new(part, contourNumber, contour.ToArray()));
+            else if (!cutoff)
+                unfinished.Add(contour.ToArray());
+            contour.Clear();
+        }
+    }
+
+    private sealed record Move(Vector? Start, Vector End, bool Rapid, LayerType Layer,
+        PostVerificationGeometry.Curve Curve);
+    private sealed record Obstacle(int Part, int Contour, IReadOnlyList<PostVerificationGeometry.Curve> Curves);
+}

OpenNest.Core/Diagnostics/PostVerificationGeometry.cs

@@ -0,0 +1,173 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using OpenNest.Geometry;
+
+namespace OpenNest.Diagnostics;
+
+/// <summary>Local native line/arc queries, without changing the engine's geometry semantics.</summary>
+internal static class PostVerificationGeometry
+{
+    internal const double Epsilon = 1e-8;
+    private const double TwoPi = 2 * System.Math.PI;
+
+    internal static void Validate(Vector point)
+    {
+        if (!double.IsFinite(point.X) || !double.IsFinite(point.Y)
+            || System.Math.Abs(point.X) > 1e12 || System.Math.Abs(point.Y) > 1e12)
+            throw new ArgumentException("Nonfinite or numerically unsupported program coordinates.");
+    }
+
+    internal static bool Closed(IReadOnlyList<Curve> curves) => curves.Count > 0
+        && curves[0].Start.DistanceTo(curves[^1].End) <= Epsilon;
+
+    internal static bool Crosses(Vector start, Vector end, IReadOnlyList<Curve> curves,
+        CancellationToken token)
+    {
+        var delta = end - start;
+        var length = start.DistanceTo(end);
+        if (length <= Epsilon)
+            return false;
+        var direction = delta * (1 / length);
+        foreach (var curve in curves)
+        {
+            token.ThrowIfCancellationRequested();
+            if (curve.ContactAfterStart(start, direction, length))
+                return true;
+        }
+        // If there are no contacts except possibly departure, all open-segment points
+        // have the same inside/outside status. A midpoint catches travel entirely inside
+        // and departure into the interior, without flagging start-only outward contact.
+        var midpoint = start + delta * 0.5;
+        var inside = false;
+        foreach (var curve in curves)
+        {
+            token.ThrowIfCancellationRequested();
+            if (curve.CrossesRay(midpoint))
+                inside = !inside;
+        }
+        return inside;
+    }
+
+    private static double Dot(Vector a, Vector b) => a.X * b.X + a.Y * b.Y;
+    private static double Cross(Vector a, Vector b) => a.X * b.Y - a.Y * b.X;
+    private static double Normalize(double angle)
+    {
+        angle %= TwoPi;
+        return angle < 0 ? angle + TwoPi : angle;
+    }
+
+    internal sealed class Curve
+    {
+        private Curve(Vector start, Vector end, Vector? center, double radius, double sweep)
+        {
+            Start = start;
+            End = end;
+            Center = center;
+            Radius = radius;
+            Sweep = sweep;
+        }
+
+        internal Vector Start { get; }
+        internal Vector End { get; }
+        private Vector? Center { get; }
+        private double Radius { get; }
+        private double Sweep { get; }
+        internal double Length => Center.HasValue ? Radius * System.Math.Abs(Sweep) : Start.DistanceTo(End);
+
+        internal static Curve Create(Vector start, Vector end, Vector? center, bool clockwise)
+        {
+            if (center is not { } c)
+                return new Curve(start, end, null, 0, 0);
+            Validate(c);
+            var radius = start.DistanceTo(c);
+            if (radius <= Epsilon || !double.IsFinite(radius)
+                || System.Math.Abs(radius - end.DistanceTo(c)) > Epsilon * System.Math.Max(1, radius))
+                throw new ArgumentException("Arc has zero or inconsistent radius.");
+            var a = System.Math.Atan2(start.Y - c.Y, start.X - c.X);
+            var b = System.Math.Atan2(end.Y - c.Y, end.X - c.X);
+            var sweep = start.DistanceTo(end) <= Epsilon ? TwoPi
+                : Normalize(clockwise ? a - b : b - a);
+            return new Curve(start, end, c, radius, clockwise ? -sweep : sweep);
+        }
+
+        private double StartAngle => System.Math.Atan2(Start.Y - Center.Value.Y, Start.X - Center.Value.X);
+        private double Travel(double angle) => Normalize(Sweep < 0 ? StartAngle - angle : angle - StartAngle);
+        private bool OnArc(Vector point) => Travel(System.Math.Atan2(point.Y - Center.Value.Y,
+            point.X - Center.Value.X)) <= System.Math.Abs(Sweep) + Epsilon / Radius
+            || point.DistanceTo(Start) <= Epsilon || point.DistanceTo(End) <= Epsilon;
+
+        internal bool ContactAfterStart(Vector origin, Vector direction, double length)
+        {
+            if (Center is { } center)
+            {
+                // Intersect the actual circle, not an inscribed chord polygon: tangencies
+                // and short arcs must not vanish between tessellation vertices.
+                var relative = center - origin;
+                var projection = Dot(relative, direction);
+                var perpendicular = Cross(relative, direction);
+                var square = Radius * Radius - perpendicular * perpendicular;
+                if (square < -Epsilon * System.Math.Max(1, Radius * 2))
+                    return false;
+                var offset = System.Math.Sqrt(System.Math.Max(0, square));
+                return Hit(projection - offset) || Hit(projection + offset);
+
+                bool Hit(double distance) => distance > Epsilon && distance <= length + Epsilon
+                    && OnArc(origin + direction * System.Math.Clamp(distance, 0, length));
+            }
+            var edge = End - Start;
+            var relativeStart = Start - origin;
+            var denominator = Cross(direction, edge);
+            if (System.Math.Abs(denominator) <= 1e-12 * System.Math.Max(1, Length))
+            {
+                if (System.Math.Abs(Cross(relativeStart, direction)) > Epsilon)
+                    return false;
+                var a = Dot(relativeStart, direction);
+                var b = Dot(End - origin, direction);
+                var low = System.Math.Max(0, System.Math.Min(a, b));
+                var high = System.Math.Min(length, System.Math.Max(a, b));
+                return high > Epsilon && low <= high + Epsilon;
+            }
+            var distanceAlongRapid = Cross(relativeStart, edge) / denominator;
+            var fractionAlongEdge = Cross(relativeStart, direction) / denominator;
+            return distanceAlongRapid > Epsilon && distanceAlongRapid <= length + Epsilon
+                && fractionAlongEdge >= -Epsilon / System.Math.Max(Length, Epsilon)
+                && fractionAlongEdge <= 1 + Epsilon / System.Math.Max(Length, Epsilon);
+        }
+
+        internal bool CrossesRay(Vector point)
+        {
+            if (Center is not { } center)
+                return (Start.Y > point.Y) != (End.Y > point.Y)
+                    && Start.X + (point.Y - Start.Y) * (End.X - Start.X) / (End.Y - Start.Y) > point.X;
+
+            // Split arcs at vertical extrema, giving monotone-Y pieces. Apply the same
+            // half-open endpoint rule as a polygon ray test, solving X on the native
+            // circle. This handles full circles, reversed arcs and shared vertices.
+            var breaks = new List<double> { 0, System.Math.Abs(Sweep) };
+            foreach (var angle in new[] { System.Math.PI / 2, 3 * System.Math.PI / 2 })
+            {
+                var travel = Travel(angle);
+                if (travel > 0 && travel < System.Math.Abs(Sweep))
+                    breaks.Add(travel);
+            }
+            breaks.Sort();
+            var inside = false;
+            for (var i = 1; i < breaks.Count; i++)
+            {
+                var a = StartAngle + System.Math.Sign(Sweep) * breaks[i - 1];
+                var b = StartAngle + System.Math.Sign(Sweep) * breaks[i];
+                var ya = i == 1 ? Start.Y : center.Y + Radius * System.Math.Sin(a);
+                var yb = i == breaks.Count - 1 ? End.Y : center.Y + Radius * System.Math.Sin(b);
+                if ((ya > point.Y) == (yb > point.Y))
+                    continue;
+                var dy = point.Y - center.Y;
+                var dx = System.Math.Sqrt(System.Math.Max(0, Radius * Radius - dy * dy));
+                var x = center.X + (System.Math.Cos((a + b) / 2) >= 0 ? dx : -dx);
+                if (x > point.X)
+                    inside = !inside;
+            }
+            return inside;
+        }
+    }
+}

OpenNest.Core/Diagnostics/PostVerificationReport.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace OpenNest.Diagnostics;
+
+public enum PostVerificationKind
+{
+    Overlap,
+    MissingLeadIn,
+    RapidCrossing,
+    Incomplete
+}
+
+/// <summary>Plate and part numbers are one-based; plate zero denotes a whole-post limitation.</summary>
+public sealed record PostVerificationFinding(PostVerificationKind Kind, int PlateNumber,
+    int? PartNumber, int? OtherPartNumber, string Message);
+
+/// <summary>Owned, immutable findings. Consent is evaluated afresh, never stored.</summary>
+public sealed class PostVerificationReport
+{
+    internal PostVerificationReport(IEnumerable<PostVerificationFinding> findings)
+    {
+        Findings = Array.AsReadOnly(findings.ToArray());
+    }
+
+    public IReadOnlyList<PostVerificationFinding> Findings { get; }
+    public bool HasWarnings => Findings.Count != 0;
+    public bool CanPost(bool risksAcknowledged) => !HasWarnings || risksAcknowledged;
+
+    public string ToDisplayText()
+    {
+        var text = new StringBuilder();
+        text.AppendLine("Pre-post verification");
+        var incomplete = Findings.Any(finding => finding.Kind == PostVerificationKind.Incomplete);
+        Summary(PostVerificationKind.Overlap, "Overlap");
+        Summary(PostVerificationKind.MissingLeadIn, "Missing lead-ins");
+        Summary(PostVerificationKind.RapidCrossing, "Rapid crossings");
+        foreach (var finding in Findings)
+        {
+            text.Append(finding.PlateNumber == 0 ? "Post processor" : $"Plate {finding.PlateNumber}");
+            if (finding.PartNumber is { } part)
+                text.Append($", part {part}");
+            if (finding.OtherPartNumber is { } other)
+                text.Append($", other part {other}");
+            text.AppendLine($": {finding.Kind}: {finding.Message}");
+        }
+        text.AppendLine("This is not a physical safety certification. The check uses direct XY rapids " +
+            "in plate/program order; the post may change order, routing or retracts. Inspect the posted " +
+            "machine program and machine setup. Actual contour gaps are not proof of adequate retention.");
+        return text.ToString();
+
+        void Summary(PostVerificationKind kind, string label)
+        {
+            var count = Findings.Count(finding => finding.Kind == kind);
+            text.AppendLine($"{label}: {count} warning(s)" +
+                (incomplete ? "; verification incomplete — do not treat as clear." : "."));
+        }
+    }
+}

OpenNest.Core/IPostVerificationSupport.cs

@@ -0,0 +1,13 @@
+namespace OpenNest;
+
+/// <summary>
+/// Optional post contract for nest-level rapid verification. Opt in only when the
+/// post preserves Plate.Parts order and each placed Program's contour order and
+/// pierce positions. This does not certify retract height, parking or controller macros.
+/// Unknown/reordering posts still get nest diagnostics, but require acknowledgment
+/// that their final rapid sequence has not been verified.
+/// </summary>
+public interface IPostVerificationSupport
+{
+    bool PreservesPlacedProgramOrder { get; }
+}

OpenNest.Tests/Diagnostics/ConsolePostVerificationTests.cs

@@ -0,0 +1,69 @@
+using System.Reflection;
+using OpenNest.CNC;
+using OpenNest.Geometry;
+using OpenNest.IO;
+
+namespace OpenNest.Tests.Diagnostics;
+
+public class ConsolePostVerificationTests
+{
+    [Fact]
+    public void RealConsoleBlocksOutputUntilExplicitRiskSwitchAndNeverRemembersConsent()
+    {
+        var directory = Path.Combine(Path.GetTempPath(), "opennest-post-verification-" + Guid.NewGuid());
+        Directory.CreateDirectory(directory);
+        try
+        {
+            var input = Path.Combine(directory, "job.nest");
+            var output = Path.Combine(directory, "job.cnc");
+            var nest = new Nest("VerificationFixture");
+            var program = new OpenNest.CNC.Program();
+            program.Codes.Add(new RapidMove(0, 0));
+            program.Codes.Add(new LinearMove(2, 0));
+            program.Codes.Add(new LinearMove(2, 2));
+            program.Codes.Add(new LinearMove(0, 2));
+            program.Codes.Add(new LinearMove(0, 0));
+            var drawing = new Drawing("square", program);
+            nest.Drawings.Add(drawing);
+            var plate = nest.CreatePlate();
+            plate.Size = new Size(10, 10);
+            plate.Parts.Add(new Part(drawing));
+            Assert.True(new NestWriter(nest).Write(input));
+            var args = new[] { input, "--quantity", "1", "--no-save", "--post", "Cincinnati CL-707",
+                "--posts-dir", AppContext.BaseDirectory, "--post-output", output };
+
+            Assert.Equal(1, Run(args));
+            Assert.False(File.Exists(output));
+
+            File.WriteAllText(output, "existing CNC must survive refusal");
+            Assert.Equal(1, Run(args));
+            Assert.Equal("existing CNC must survive refusal", File.ReadAllText(output));
+
+            var colliding = args.Where(arg => arg != "--no-save")
+                .Concat(new[] { "--output", Path.Combine(directory, ".", "job.cnc") }).ToArray();
+            Assert.Equal(1, Run(colliding));
+            Assert.Equal("existing CNC must survive refusal", File.ReadAllText(output));
+            Assert.Equal(1, Run(colliding.Append("--acknowledge-post-risks").ToArray()));
+            Assert.Equal("existing CNC must survive refusal", File.ReadAllText(output));
+
+            Assert.Equal(0, Run(args.Append("--acknowledge-post-risks").ToArray()));
+            var posted = File.ReadAllText(output);
+            Assert.Contains("M30", posted);
+            Assert.Contains("VerificationFixture", posted);
+
+            Assert.Equal(1, Run(args));
+            Assert.Equal(posted, File.ReadAllText(output));
+        }
+        finally
+        {
+            Directory.Delete(directory, recursive: true);
+        }
+    }
+
+    private static int Run(string[] args)
+    {
+        var entry = Assembly.Load("OpenNest.Console").GetType("NestConsole")!
+            .GetMethod("Run", BindingFlags.Public | BindingFlags.Static)!;
+        return (int)entry.Invoke(null, new object[] { args })!;
+    }
+}

OpenNest.Tests/Diagnostics/PostVerificationAnalyzerTests.cs

@@ -0,0 +1,482 @@
+using OpenNest.CNC;
+using OpenNest.CNC.CuttingStrategy;
+using OpenNest.Diagnostics;
+using OpenNest.Geometry;
+
+namespace OpenNest.Tests.Diagnostics;
+
+public class PostVerificationAnalyzerTests
+{
+    [Fact]
+    public void EmptyReport_ListsAllChecksAndLimits()
+    {
+        var report = PostVerificationAnalyzer.Analyze(new Nest());
+        Assert.Empty(report.Findings);
+        Assert.False(report.HasWarnings);
+        Assert.True(report.CanPost(false));
+        Assert.True(report.CanPost(true));
+        var text = report.ToDisplayText();
+        Assert.Contains("Overlap", text);
+        Assert.Contains("Missing lead-ins", text);
+        Assert.Contains("Rapid crossings", text);
+        Assert.Contains("not a physical safety certification", text);
+        Assert.Contains("retract", text);
+        Assert.Contains("routing", text);
+    }
+
+    [Fact]
+    public void Overlap_UsesCleanMaterialAndOriginalOneBasedIndices()
+    {
+        var a = Rectangle(0, 0, 4);
+        var b = Rectangle(1, 1, 1);
+        // Deliberately unrelated placed toolpaths: overlap must use clean drawings.
+        a.Program.Codes.Clear();
+        a.Program.MoveTo(100, 100);
+        a.Program.LineTo(101, 101);
+        var report = Analyze(Cutoff(30, 30), a, Scribe(40, 40), b);
+        var overlap = Assert.Single(Find(report, PostVerificationKind.Overlap));
+        Assert.Equal((1, 2, 4), (overlap.PlateNumber, overlap.PartNumber, overlap.OtherPartNumber));
+        Assert.True(report.HasWarnings);
+        Assert.False(report.CanPost(false));
+        Assert.True(report.CanPost(true));
+        Assert.False(report.CanPost(false)); // Consent is supplied per invocation, never latched.
+    }
+
+    [Fact]
+    public void Overlap_SubtractsHoles()
+    {
+        var program = Square(0, 0, 10);
+        program.Codes.AddRange(Square(2, 2, 6).Codes);
+        var frame = Part(program);
+        var report = Analyze(frame, Rectangle(3, 3, 1));
+        Assert.Empty(Find(report, PostVerificationKind.Overlap));
+        Assert.Empty(Find(report, PostVerificationKind.Incomplete));
+    }
+
+    [Fact]
+    public void MissingLeadIn_ManualFlagDoesNotProveCoverage()
+    {
+        var part = Rectangle(0, 0, 4);
+        part.HasManualLeadIns = true;
+        Assert.Single(Find(Analyze(part), PostVerificationKind.MissingLeadIn));
+    }
+
+    [Fact]
+    public void MissingLeadIn_ActualLeadDoesNotRequireManualFlag()
+    {
+        var part = Rectangle(0, 0, 4);
+        part.ApplyLeadIns(Leads(), new Vector(-2, -2));
+        part.HasManualLeadIns = false;
+        Assert.Empty(Find(Analyze(part), PostVerificationKind.MissingLeadIn));
+    }
+
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public void MissingLeadIn_NoLeadOrZeroLengthWarns(bool zeroLength)
+    {
+        var part = Rectangle(0, 0, 4);
+        var parameters = Leads();
+        parameters.ExternalLeadIn = zeroLength ? new LineLeadIn { Length = 0 } : new NoLeadIn();
+        part.ApplyLeadIns(parameters, new Vector(-2, -2));
+        Assert.Single(Find(Analyze(part), PostVerificationKind.MissingLeadIn));
+    }
+
+    [Fact]
+    public void MissingLeadIn_PartialApplySingleLeavesOtherContourUncovered()
+    {
+        var program = Square(0, 0, 10);
+        program.Codes.AddRange(Square(2, 2, 2).Codes);
+        var part = Part(program);
+        part.ApplySingleLeadIn(Leads(), Vector.Zero,
+            new Line(Vector.Zero, new Vector(10, 0)), ContourType.External);
+        Assert.True(part.HasManualLeadIns);
+        Assert.Single(Find(Analyze(part), PostVerificationKind.MissingLeadIn));
+    }
+
+    [Fact]
+    public void ScribeAndCutoff_AreExemptFromOverlapAndLeadInChecks()
+    {
+        var report = Analyze(Scribe(0, 0), Cutoff(0, 0));
+        Assert.Empty(report.Findings);
+    }
+
+    [Fact]
+    public void Rapid_ThroughPreviouslyCutPartWarns()
+    {
+        var report = Analyze(Rectangle(0, 0, 4), Scribe(-2, 2), Scribe(6, 2));
+        Assert.Contains(Find(report, PostVerificationKind.RapidCrossing), f =>
+            f.PartNumber == 3 && f.OtherPartNumber == 1);
+    }
+
+    [Fact]
+    public void Rapid_DoesNotUseFuturePartsAsObstacles()
+    {
+        var report = Analyze(Scribe(-2, 2), Scribe(6, 2), Rectangle(0, 0, 4));
+        Assert.Empty(Find(report, PostVerificationKind.RapidCrossing));
+    }
+
+    [Theory]
+    [InlineData(-2, -2, false)] // Start-only departure.
+    [InlineData(2, 2, true)] // Departure into the interior.
+    [InlineData(4, 0, true)] // Along edge / arrival on another endpoint.
+    public void Rapid_HandlesDepartureVersusInteriorAndBoundary(double x, double y, bool warning)
+    {
+        var report = Analyze(Rectangle(0, 0, 4), Scribe(x, y));
+        Assert.Equal(warning, Find(report, PostVerificationKind.RapidCrossing).Any());
+    }
+
+    [Theory]
+    [InlineData(-2, 4, 6, 4)] // Tangent along top edge.
+    [InlineData(-2, 2, 0, 2)] // Endpoint arrival.
+    [InlineData(1, 1, 2, 2)] // Entirely inside.
+    public void Rapid_ConservativelyFlagsContactAndInterior(double x1, double y1, double x2, double y2)
+    {
+        var report = Analyze(Rectangle(0, 0, 4), Scribe(x1, y1), Scribe(x2, y2));
+        Assert.Contains(Find(report, PostVerificationKind.RapidCrossing), f => f.PartNumber == 3);
+    }
+
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public void Rapid_ActualGapNotStaleTabSettingControlsObstacle(bool staleFlag)
+    {
+        var closed = Rectangle(0, 0, 4);
+        closed.CuttingParameters = new CuttingParameters { TabsEnabled = staleFlag };
+        Assert.Contains(Find(Analyze(closed, Scribe(-2, 2), Scribe(6, 2)),
+            PostVerificationKind.RapidCrossing), f => f.PartNumber == 3);
+
+        var gapped = Rectangle(0, 0, 4);
+        ((LinearMove)gapped.Program.Codes[^1]).EndPoint = new Vector(0, 0.25);
+        gapped.CuttingParameters = new CuttingParameters { TabsEnabled = staleFlag };
+        Assert.Empty(Find(Analyze(gapped, Scribe(-2, 2), Scribe(6, 2)),
+            PostVerificationKind.RapidCrossing));
+    }
+
+    [Fact]
+    public void Rapid_RealGeneratedTabRemainsGapWithStaleDisabledParameters()
+    {
+        var part = Rectangle(0, 0, 4);
+        var parameters = Leads();
+        parameters.TabsEnabled = true;
+        parameters.TabConfig = new NormalTab { Size = 0.25 };
+        part.ApplyLeadIns(parameters, new Vector(-2, 0));
+        parameters.TabsEnabled = false;
+        Assert.Empty(Find(Analyze(part, Scribe(-2, 2), Scribe(6, 2)), PostVerificationKind.RapidCrossing));
+    }
+
+    [Fact]
+    public void Rapid_CutoffTravelStillCrossesEarlierRealCuts()
+    {
+        var report = Analyze(Rectangle(0, 0, 4), Scribe(-2, 2), Cutoff(6, 2));
+        Assert.Contains(Find(report, PostVerificationKind.RapidCrossing), f =>
+            f.PartNumber == 3 && f.OtherPartNumber == 1);
+    }
+
+    [Theory]
+    [InlineData(Mode.Absolute)]
+    [InlineData(Mode.Incremental)]
+    public void Rapid_SamePartSharedHoleCallsUseOffsetsAndNonzeroLeadOrigins(Mode mode)
+    {
+        var part = Rectangle(100, 50, 20);
+        var hole = CircleWithLead();
+        hole.Mode = mode;
+        var placed = new Program();
+        placed.Codes.Add(new SubProgramCall { Program = hole, Offset = new Vector(5, 5), Id = 7 });
+        placed.MoveTo(2, 5);
+        placed.LineTo(2, 5); // Zero-length cut doesn't create an obstacle.
+        placed.MoveTo(8, 5); // Cross completed first hole.
+        placed.Codes.Add(new SubProgramCall { Program = hole, Offset = new Vector(15, 5), Id = 7 });
+        placed.Mode = mode;
+        Assert.True(part.RestoreLeadInProgram(placed, false));
+        var report = Analyze(part);
+        Assert.Contains(Find(report, PostVerificationKind.RapidCrossing), f =>
+            f.PartNumber == 1 && f.OtherPartNumber == 1);
+        Assert.Empty(Find(report, PostVerificationKind.Incomplete));
+    }
+
+    [Theory]
+    [InlineData(Mode.Absolute)]
+    [InlineData(Mode.Incremental)]
+    public void Rapid_NonzeroInitialLeadRapidIsNotAppliedTwice(Mode mode)
+    {
+        var part = Rectangle(100, 50, 4);
+        var placed = Square(0, 0, 4);
+        placed.Codes.Insert(0, new RapidMove(-2, 0));
+        placed.Codes[1] = new LinearMove(0, 0) { Layer = LayerType.Leadin };
+        placed.MoveTo(-2, 2);
+        placed.MoveTo(6, 2);
+        placed.Mode = mode;
+        part.RestoreLeadInProgram(placed, false);
+        var crossings = Find(Analyze(part), PostVerificationKind.RapidCrossing);
+        Assert.Single(crossings);
+        Assert.Empty(Find(Analyze(part), PostVerificationKind.MissingLeadIn));
+    }
+
+    [Theory]
+    [InlineData(RotationType.CW)]
+    [InlineData(RotationType.CCW)]
+    public void Rapid_FullCircleArcTangentIsNotLostToChordApproximation(RotationType rotation)
+    {
+        var program = new Program();
+        program.MoveTo(1, 0);
+        program.ArcTo(1, 0, 0, 0, rotation);
+        var report = Analyze(Part(program), Scribe(-2, 1), Scribe(2, 1));
+        Assert.Contains(Find(report, PostVerificationKind.RapidCrossing), f => f.PartNumber == 3);
+    }
+
+    [Fact]
+    public void Rapid_SamePartFutureContourIsNotAnObstacle()
+    {
+        var part = Rectangle(0, 0, 10);
+        var placed = new Program();
+        placed.MoveTo(-2, 2);
+        placed.MoveTo(6, 2);
+        placed.Codes.AddRange(Square(0, 0, 4).Codes);
+        part.RestoreLeadInProgram(placed, false);
+        Assert.Empty(Find(Analyze(part), PostVerificationKind.RapidCrossing));
+    }
+
+    [Fact]
+    public void MultiplePlates_AreAllCheckedWithoutSharingObstacles()
+    {
+        var nest = NestWith(Rectangle(0, 0, 4));
+        var second = nest.CreatePlate();
+        second.Parts.Add(Scribe(-2, 2));
+        second.Parts.Add(Scribe(6, 2));
+        second.Parts.Add(Rectangle(0, 0, 4));
+        second.Parts.Add(Rectangle(1, 1, 1));
+        var report = PostVerificationAnalyzer.Analyze(nest);
+        Assert.Contains(Find(report, PostVerificationKind.MissingLeadIn), f => f.PlateNumber == 1);
+        Assert.Contains(Find(report, PostVerificationKind.MissingLeadIn), f => f.PlateNumber == 2);
+        Assert.All(Find(report, PostVerificationKind.Overlap), f => Assert.Equal(2, f.PlateNumber));
+        Assert.DoesNotContain(Find(report, PostVerificationKind.RapidCrossing), f =>
+            f.PlateNumber == 2 && f.PartNumber <= 3);
+    }
+
+    [Theory]
+    [InlineData("recursive")]
+    [InlineData("missing-call")]
+    [InlineData("null-code")]
+    [InlineData("nonfinite")]
+    [InlineData("bad-arc")]
+    [InlineData("empty")]
+    [InlineData("null-codes")]
+    public void MalformedPlacedPrograms_WarnInsteadOfClearing(string fault)
+    {
+        var part = Rectangle(0, 0, 4);
+        var program = part.Program;
+        switch (fault)
+        {
+            case "recursive": program.Codes.Add(new SubProgramCall { Program = program }); break;
+            case "missing-call": program.Codes.Add(new SubProgramCall()); break;
+            case "null-code": program.Codes.Add(null); break;
+            case "nonfinite": program.MoveTo(double.NaN, 0); break;
+            case "bad-arc": program.ArcTo(1, 1, 0, 0, RotationType.CW); break;
+            case "empty": program.Codes.Clear(); break;
+            case "null-codes": program.Codes = null; break;
+        }
+        var report = Analyze(part);
+        Assert.NotEmpty(Find(report, PostVerificationKind.Incomplete));
+        Assert.True(report.HasWarnings);
+        Assert.False(report.CanPost(false));
+        Assert.DoesNotContain("No warnings", report.ToDisplayText());
+    }
+
+    [Fact]
+    public void MalformedCleanProgram_OverlapIssuePreservesInputIndex()
+    {
+        var part = Rectangle(0, 0, 4);
+        part.BaseDrawing.Program.Codes.RemoveAt(4);
+        var report = Analyze(Cutoff(30, 30), part);
+        Assert.Contains(Find(report, PostVerificationKind.Incomplete), f => f.PartNumber == 2);
+    }
+
+    [Fact]
+    public void Rapid_ResumedContourBecomesObstacleOnlyAfterItsLastCut()
+    {
+        var part = Rectangle(0, 0, 4);
+        var placed = Square(0, 0, 4);
+        placed.Codes.Insert(3, new RapidMove(4, 4)); // Pause, with no uncut gap.
+        placed.MoveTo(-2, 2);
+        placed.MoveTo(6, 2);
+        part.RestoreLeadInProgram(placed, false);
+        Assert.Single(Find(Analyze(part), PostVerificationKind.RapidCrossing));
+    }
+
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public void Rapid_InternalGapDoesNotBecomeAnObstacle(bool staleFlag)
+    {
+        var part = Rectangle(0, 0, 4);
+        var placed = Square(0, 0, 4);
+        placed.Codes.Insert(3, new RapidMove(3.75, 4)); // Leave a gap on the top edge.
+        placed.MoveTo(-2, 2);
+        placed.MoveTo(6, 2);
+        part.RestoreLeadInProgram(placed, false);
+        part.CuttingParameters = new CuttingParameters { TabsEnabled = staleFlag };
+        Assert.Empty(Find(Analyze(part), PostVerificationKind.RapidCrossing));
+    }
+
+    [Fact]
+    public void MissingPlacedCuts_CannotPassForACleanMaterialPart()
+    {
+        var part = Rectangle(0, 0, 4);
+        part.Program.Codes.Clear();
+        part.Program.MoveTo(0, 0);
+        var report = Analyze(part);
+        Assert.NotEmpty(Find(report, PostVerificationKind.Incomplete));
+        Assert.False(report.CanPost(false));
+    }
+
+    [Fact]
+    public void InvalidArcDirection_IsIncomplete()
+    {
+        var part = Part(CircleWithLead());
+        ((ArcMove)part.Program.Codes[^1]).Rotation = (RotationType)99;
+        Assert.NotEmpty(Find(Analyze(part), PostVerificationKind.Incomplete));
+    }
+
+    [Fact]
+    public void Rapid_LeadOutThatCompletesTabGapIsNotTreatedAsRetained()
+    {
+        var part = Rectangle(0, 0, 4);
+        ((LinearMove)part.Program.Codes[^1]).EndPoint = new Vector(0, 0.25);
+        part.Program.Codes.Add(new LinearMove(0, 0) { Layer = LayerType.Leadout });
+        var report = Analyze(part, Scribe(-2, 2), Scribe(6, 2));
+        Assert.True(Find(report, PostVerificationKind.RapidCrossing).Any()
+            || Find(report, PostVerificationKind.Incomplete).Any());
+    }
+
+    [Fact]
+    public void Rapid_OutOfOrderFragmentsCannotSilentlyPassAsTabbed()
+    {
+        var part = Rectangle(0, 0, 4);
+        var program = new Program();
+        program.MoveTo(0, 0);
+        program.LineTo(4, 0);
+        program.MoveTo(4, 4);
+        program.LineTo(0, 4);
+        program.MoveTo(4, 0);
+        program.LineTo(4, 4);
+        program.MoveTo(0, 4);
+        program.LineTo(0, 0);
+        part.RestoreLeadInProgram(program, false);
+        var report = Analyze(part, Scribe(-2, 2), Scribe(6, 2));
+        Assert.True(Find(report, PostVerificationKind.RapidCrossing).Any()
+            || Find(report, PostVerificationKind.Incomplete).Any());
+    }
+
+    [Fact]
+    public void Cancellation_ThrowsWithoutChangingInputs()
+    {
+        var part = Rectangle(0, 0, 4);
+        var before = part.Program.ToString();
+        using var cancellation = new CancellationTokenSource();
+        cancellation.Cancel();
+        Assert.Throws<OperationCanceledException>(() =>
+            PostVerificationAnalyzer.Analyze(NestWith(part), cancellation.Token));
+        Assert.Equal(before, part.Program.ToString());
+    }
+
+    [Fact]
+    public void Analyze_PreservesProgramsPosesSharedCallsAndCuttingState()
+    {
+        var part = Rectangle(100, 50, 20);
+        var sub = CircleWithLead();
+        var program = Square(0, 0, 20);
+        program.Codes.Insert(0, new SubProgramCall { Program = sub, Offset = new Vector(5, 5) });
+        program.Codes.Insert(1, new SubProgramCall { Program = sub, Offset = new Vector(15, 5) });
+        program.Mode = Mode.Incremental;
+        part.RestoreLeadInProgram(program, true);
+        part.CuttingParameters = Leads();
+        var nest = NestWith(part);
+        var codes = program.Codes.ToArray();
+        var before = program.ToString();
+        var beforeSub = sub.ToString();
+        var parameters = part.CuttingParameters;
+        var bounds = part.BoundingBox;
+        var quantity = part.BaseDrawing.Quantity.Nested;
+        var report = PostVerificationAnalyzer.Analyze(nest);
+        Assert.Same(program, part.Program);
+        Assert.Equal(codes, program.Codes);
+        Assert.Equal(before, program.ToString());
+        Assert.Equal(beforeSub, sub.ToString());
+        Assert.Same(sub, ((SubProgramCall)program[0]).Program);
+        Assert.Same(sub, ((SubProgramCall)program[1]).Program);
+        Assert.Equal(new Vector(100, 50), part.Location);
+        Assert.Same(bounds, part.BoundingBox);
+        Assert.True(part.HasManualLeadIns);
+        Assert.True(part.LeadInsLocked);
+        Assert.Same(parameters, part.CuttingParameters);
+        Assert.Equal(quantity, part.BaseDrawing.Quantity.Nested);
+        Assert.True(((ICollection<PostVerificationFinding>)report.Findings).IsReadOnly);
+        var display = report.ToDisplayText();
+        part.Program.Codes.Clear();
+        Assert.Equal(display, report.ToDisplayText());
+    }
+
+    private static PostVerificationFinding[] Find(PostVerificationReport report, PostVerificationKind kind) =>
+        report.Findings.Where(f => f.Kind == kind).ToArray();
+
+    private static PostVerificationReport Analyze(params Part[] parts) =>
+        PostVerificationAnalyzer.Analyze(NestWith(parts));
+
+    private static Nest NestWith(params Part[] parts)
+    {
+        var nest = new Nest();
+        var plate = nest.CreatePlate();
+        foreach (var part in parts)
+            plate.Parts.Add(part);
+        return nest;
+    }
+
+    private static Part Part(Program program) => new(new Drawing("fixture", program));
+
+    private static Part Rectangle(double x, double y, double size) =>
+        new(new Drawing("rectangle", Square(0, 0, size)), new Vector(x, y));
+
+    private static Program Square(double x, double y, double size)
+    {
+        var program = new Program();
+        program.MoveTo(x, y);
+        program.LineTo(x + size, y);
+        program.LineTo(x + size, y + size);
+        program.LineTo(x, y + size);
+        program.LineTo(x, y);
+        return program;
+    }
+
+    private static Part Scribe(double x, double y)
+    {
+        var program = new Program();
+        program.MoveTo(x, y);
+        program.Codes.Add(new LinearMove(x, y) { Layer = LayerType.Scribe });
+        return Part(program);
+    }
+
+    private static Part Cutoff(double x, double y)
+    {
+        var program = new Program();
+        program.MoveTo(x, y);
+        program.LineTo(x + 1, y);
+        return new Part(new Drawing("cutoff", program) { IsCutOff = true });
+    }
+
+    private static Program CircleWithLead()
+    {
+        var program = new Program();
+        program.MoveTo(0.5, 0);
+        program.Codes.Add(new LinearMove(1, 0) { Layer = LayerType.Leadin });
+        program.Codes.Add(new ArcMove(1, 0, 0, 0) { Layer = LayerType.Display });
+        return program;
+    }
+
+    private static CuttingParameters Leads() => new()
+    {
+        ExternalLeadIn = new LineLeadIn { Length = 0.5 },
+        InternalLeadIn = new LineLeadIn { Length = 0.5 },
+        ArcCircleLeadIn = new LineLeadIn { Length = 0.5 }
+    };
+}

OpenNest.Tests/Diagnostics/PostVerificationPostContractTests.cs

@@ -0,0 +1,56 @@
+using OpenNest.CNC.CuttingStrategy;
+using OpenNest.Diagnostics;
+using OpenNest.Geometry;
+using OpenNest.Posts.Cincinnati;
+using OpenNest.Posts.CincinnatiCIFiber;
+using OpenNest.Posts.GravographIS;
+
+namespace OpenNest.Tests.Diagnostics;
+
+public class PostVerificationPostContractTests
+{
+    [Fact]
+    public void ReorderingPostsRequireAcknowledgmentEvenWhenNestChecksAreClear()
+    {
+        var nest = ClearNest();
+        Assert.False(PostVerificationAnalyzer.Analyze(nest).HasWarnings);
+        IPostProcessor[] posts =
+        [
+            new CincinnatiPostProcessor(new CincinnatiPostConfig()),
+            new GravographISPostProcessor(new GravographISPostConfig())
+        ];
+        foreach (var post in posts)
+        {
+            var report = PostVerificationAnalyzer.AnalyzeForPost(nest, post);
+            Assert.Contains(report.Findings, finding => finding.Kind == PostVerificationKind.Incomplete);
+            Assert.False(report.CanPost(false));
+            Assert.True(report.CanPost(true));
+            Assert.Contains(post.Name, report.ToDisplayText());
+        }
+    }
+
+    [Fact]
+    public void CIFiberUsesPlacedOrderWithoutAnExtraOrderWarning()
+    {
+        var report = PostVerificationAnalyzer.AnalyzeForPost(ClearNest(),
+            new CIFiberPostProcessor(new CIFiberPostConfig()));
+        Assert.Empty(report.Findings);
+        Assert.True(report.CanPost(false));
+    }
+
+    private static Nest ClearNest()
+    {
+        var program = new OpenNest.CNC.Program();
+        program.MoveTo(0, 0);
+        program.LineTo(4, 0);
+        program.LineTo(4, 4);
+        program.LineTo(0, 4);
+        program.LineTo(0, 0);
+        var part = new Part(new Drawing("square", program));
+        part.ApplyLeadIns(new CuttingParameters { ExternalLeadIn = new LineLeadIn { Length = 0.5 } },
+            new Vector(-2, -2));
+        var nest = new Nest();
+        nest.CreatePlate().Parts.Add(part);
+        return nest;
+    }
+}

OpenNest.Tests/OpenNest.Tests.csproj

@@ -23,6 +23,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\OpenNest.Api\OpenNest.Api.csproj" />
+    <ProjectReference Include="..\OpenNest.Console\OpenNest.Console.csproj" />
     <ProjectReference Include="..\OpenNest.Benchmark\OpenNest.Benchmark.csproj" />
     <ProjectReference Include="..\OpenNest.Data\OpenNest.Data.csproj" />
     <ProjectReference Include="..\OpenNest.Core\OpenNest.Core.csproj" />

OpenNest.WinForms.Tests/Forms/PostVerificationFormTests.cs

@@ -0,0 +1,223 @@
+using System.Reflection;
+using System.Runtime.ExceptionServices;
+using System.Windows.Forms;
+using OpenNest.CNC;
+using OpenNest.Diagnostics;
+using OpenNest.Forms;
+
+namespace OpenNest.WinForms.Tests.Forms;
+
+public class PostVerificationFormTests
+{
+#pragma warning disable xUnit1031 // Dedicated STA; only await completed tasks, or explicitly pump until completion.
+    [Fact]
+    public void WarningsRequireFreshAcknowledgmentAndUncheckingRevokesPermission()
+    {
+        RunSta(() =>
+        {
+            var nest = WarningNest();
+            using var form = new PostVerificationForm(nest,
+                (_, _) => Task.FromResult(PostVerificationAnalyzer.Analyze(nest)));
+            form.VerifyAsync().GetAwaiter().GetResult();
+            var consent = Control<CheckBox>(form, "acknowledgeBox");
+            var post = Control<Button>(form, "postButton");
+            Assert.False(consent.Checked);
+            Assert.False(post.Enabled);
+            Invoke(form, "PostButton_Click", null, EventArgs.Empty);
+            Assert.NotEqual(DialogResult.OK, form.DialogResult);
+            consent.Checked = true;
+            Assert.True(post.Enabled);
+            consent.Checked = false;
+            Assert.False(post.Enabled);
+            consent.Checked = true;
+            Invoke(form, "PostButton_Click", null, EventArgs.Empty);
+            Assert.Equal(DialogResult.OK, form.DialogResult);
+
+            using var retry = new PostVerificationForm(nest,
+                (_, _) => Task.FromResult(PostVerificationAnalyzer.Analyze(nest)));
+            retry.VerifyAsync().GetAwaiter().GetResult();
+            Assert.False(Control<CheckBox>(retry, "acknowledgeBox").Checked);
+            Assert.False(Control<Button>(retry, "postButton").Enabled);
+        });
+    }
+
+    [Fact]
+    public void ClearReportIsDisplayedAndCancelIsDefault()
+    {
+        RunSta(() =>
+        {
+            var nest = WarningNest();
+            foreach (var move in nest.Plates[0].Parts[0].Program.Codes.OfType<LinearMove>())
+                move.Layer = LayerType.Scribe;
+            foreach (var move in nest.Plates[0].Parts[0].BaseDrawing.Program.Codes.OfType<LinearMove>())
+                move.Layer = LayerType.Scribe;
+            using var form = new PostVerificationForm(nest,
+                (_, _) => Task.FromResult(PostVerificationAnalyzer.Analyze(nest)));
+            form.VerifyAsync().GetAwaiter().GetResult();
+            Assert.NotEmpty(Control<TextBox>(form, "reportBox").Text);
+            Assert.True(Control<Button>(form, "postButton").Enabled);
+            Assert.False(Control<CheckBox>(form, "acknowledgeBox").Enabled);
+            Assert.Equal("Continue Posting", Control<Button>(form, "postButton").Text);
+            Assert.Same(Control<Button>(form, "cancelButton"), form.AcceptButton);
+            Assert.Same(Control<Button>(form, "cancelButton"), form.CancelButton);
+        });
+    }
+
+    [Fact]
+    public void UnexpectedFailureCannotBeOverridden()
+    {
+        RunSta(() =>
+        {
+            using var form = new PostVerificationForm(WarningNest(),
+                (_, _) => Task.FromException<PostVerificationReport>(new InvalidOperationException("test failure")));
+            form.VerifyAsync().GetAwaiter().GetResult();
+            Control<CheckBox>(form, "acknowledgeBox").Checked = true;
+            Assert.False(Control<Button>(form, "postButton").Enabled);
+            Assert.Contains("test failure", Control<TextBox>(form, "reportBox").Text);
+            Invoke(form, "PostButton_Click", null, EventArgs.Empty);
+            Assert.NotEqual(DialogResult.OK, form.DialogResult);
+        });
+    }
+
+    [Fact]
+    public void DisposalIsIdempotent()
+    {
+        RunSta(() =>
+        {
+            var form = new PostVerificationForm(WarningNest());
+            form.Dispose();
+            form.Dispose();
+        });
+    }
+
+    [Fact]
+    public void ClosingDuringVerificationWaitsForWorkerAndDiscardsLateResult()
+    {
+        RunSta(() =>
+        {
+            var pending = new TaskCompletionSource<PostVerificationReport>();
+            var nest = WarningNest();
+            var token = CancellationToken.None;
+            using var form = new PostVerificationForm(nest, (_, cancellation) =>
+            {
+                token = cancellation;
+                return pending.Task;
+            });
+            var work = form.VerifyAsync();
+            try
+            {
+                var closing = new FormClosingEventArgs(CloseReason.UserClosing, false);
+                Invoke(form, "OnFormClosing", closing);
+                Assert.True(closing.Cancel);
+                Assert.True(token.IsCancellationRequested);
+                Assert.False(work.IsCompleted);
+                pending.SetResult(PostVerificationAnalyzer.Analyze(nest));
+                var until = DateTime.UtcNow.AddSeconds(10);
+                while (!work.IsCompleted && DateTime.UtcNow < until)
+                    Application.DoEvents();
+                Assert.True(work.IsCompleted);
+                work.GetAwaiter().GetResult();
+                Assert.NotEqual(DialogResult.OK, form.DialogResult);
+            }
+            finally
+            {
+                pending.TrySetCanceled();
+            }
+        });
+    }
+
+    [Theory]
+    [InlineData("Cancel")]
+    [InlineData("Escape")]
+    [InlineData("Close")]
+    public void RealModalCancellationKeepsOwnerDisabledUntilWorkerStops(string action)
+    {
+        RunSta(() =>
+        {
+            var pending = new TaskCompletionSource<PostVerificationReport>();
+            using var owner = new Form();
+            using var form = new PostVerificationForm(WarningNest(), (_, _) => pending.Task);
+            Exception? failure = null;
+            owner.Show();
+            using var timeout = new System.Windows.Forms.Timer { Interval = 10000 };
+            timeout.Tick += (_, _) =>
+            {
+                failure ??= new TimeoutException("Modal cancellation did not finish.");
+                pending.TrySetCanceled();
+                form.Close();
+            };
+            form.Shown += (_, _) => form.BeginInvoke(new System.Action(() =>
+            {
+                try
+                {
+                    Assert.False(IsWindowEnabled(owner.Handle));
+                    if (action == "Cancel")
+                        Control<Button>(form, "cancelButton").PerformClick();
+                    else if (action == "Escape")
+                        Invoke(form, "ProcessDialogKey", Keys.Escape);
+                    else
+                        form.Close();
+
+                    // ShowDialog must stay active while the worker ignores cancellation.
+                    Assert.True(form.Visible);
+                    Assert.False(IsWindowEnabled(owner.Handle));
+                    Assert.False(Control<Button>(form, "postButton").Enabled);
+                }
+                catch (Exception ex)
+                {
+                    failure = ex;
+                }
+                finally
+                {
+                    pending.TrySetCanceled();
+                }
+            }));
+            timeout.Start();
+            var result = form.ShowDialog(owner);
+            timeout.Stop();
+            Assert.Equal(DialogResult.Cancel, result);
+            Assert.True(IsWindowEnabled(owner.Handle));
+            if (failure != null)
+                ExceptionDispatchInfo.Capture(failure).Throw();
+        });
+    }
+
+    [System.Runtime.InteropServices.DllImport("user32.dll")]
+    [return: System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.Bool)]
+    private static extern bool IsWindowEnabled(IntPtr window);
+
+    private static Nest WarningNest()
+    {
+        var nest = new Nest("verification");
+        var program = new CNC.Program();
+        program.Codes.Add(new RapidMove(0, 0));
+        program.Codes.Add(new LinearMove(5, 0));
+        program.Codes.Add(new LinearMove(5, 5));
+        program.Codes.Add(new LinearMove(0, 5));
+        program.Codes.Add(new LinearMove(0, 0));
+        nest.CreatePlate().Parts.Add(new Part(new Drawing("square", program)));
+        return nest;
+    }
+
+    private static T Control<T>(Form form, string name) where T : Control =>
+        Assert.IsType<T>(form.Controls.Find(name, true).Single());
+
+    private static void Invoke(Form form, string method, params object?[] arguments) =>
+        form.GetType().GetMethod(method, BindingFlags.Instance | BindingFlags.NonPublic)!
+            .Invoke(form, arguments);
+
+    private static void RunSta(System.Action action)
+    {
+        Exception? failure = null;
+        var thread = new Thread(() =>
+        {
+            try { action(); }
+            catch (Exception ex) { failure = ex; }
+        });
+        thread.SetApartmentState(ApartmentState.STA);
+        thread.Start();
+        Assert.True(thread.Join(TimeSpan.FromSeconds(30)), "STA verification test timed out.");
+        if (failure != null)
+            ExceptionDispatchInfo.Capture(failure).Throw();
+    }
+}

OpenNest/Forms/MainForm.cs

@@ -1488,36 +1488,60 @@ namespace OpenNest.Forms
             var menuItem = (ToolStripMenuItem)sender;
             var postProcessor = menuItem.Tag as IPostProcessor;
 
-            if (postProcessor == null)
+            var editForm = activeForm;
+            if (postProcessor == null || editForm == null)
                 return;
 
+            // Closed progress windows can still have a fill awaiting its final commit.
+            // Keep the nest stable throughout verification and all owned modal dialogs.
+            var views = MdiChildren.OfType<EditNestForm>()
+                .Where(form => ReferenceEquals(form.Nest, editForm.Nest))
+                .Select(form => form.PlateView).ToArray();
+            if (nestingInProgress || Application.OpenForms.OfType<NestProgressForm>().Any()
+                || views.Any(view => view.IsFillInProgress || view.Actions.CurrentAction?.IsBusy() == true))
+            {
+                MessageBox.Show(this, "Finish or cancel the current nesting or plate action before posting.",
+                    "Verify Nest Before Posting", MessageBoxButtons.OK, MessageBoxIcon.Information);
+                return;
+            }
+
+            foreach (var view in views)
+                view.SetAction(typeof(ActionSelect));
+            var nest = editForm.Nest;
+
             if (postProcessor is IPostProcessorNestAware nestAware)
-                nestAware.PrepareForNest(activeForm.Nest);
+                nestAware.PrepareForNest(nest);
 
             if (postProcessor is IConfigurablePostProcessor configurable)
             {
                 using var configForm = new PostProcessorConfigForm(configurable);
-                if (configForm.ShowDialog() != DialogResult.OK)
+                if (configForm.ShowDialog(this) != DialogResult.OK)
                     return;
             }
 
-            var dialog = new SaveFileDialog();
-            dialog.Filter = "CNC File (*.cnc) | *.cnc";
-            dialog.FileName = activeForm.Nest.Name;
+            using (var verification = new PostVerificationForm(nest, postProcessor))
+            {
+                if (verification.ShowDialog(this) != DialogResult.OK)
+                    return;
+            }
 
-            if (dialog.ShowDialog() == DialogResult.OK)
+            using var dialog = new SaveFileDialog();
+            dialog.Filter = "CNC File (*.cnc) | *.cnc";
+            dialog.FileName = nest.Name;
+
+            if (dialog.ShowDialog(this) == DialogResult.OK)
             {
                 var path = dialog.FileName;
 
                 if (postProcessor is IMultiFilePostProcessor multiFile)
                 {
-                    var files = multiFile.GetOutputFiles(activeForm.Nest, path);
+                    var files = multiFile.GetOutputFiles(nest, path);
                     if (!ConfirmOverwrite(files, path))
                         return;
 
                     try
                     {
-                        postProcessor.Post(activeForm.Nest, path);
+                        postProcessor.Post(nest, path);
                     }
                     catch (Exception ex)
                         when (ex is InvalidOperationException or IOException or UnauthorizedAccessException)
@@ -1545,7 +1569,7 @@ namespace OpenNest.Forms
                     return;
                 }
 
-                postProcessor.Post(activeForm.Nest, path);
+                postProcessor.Post(nest, path);
             }
         }
 

OpenNest/Forms/PostVerificationForm.Designer.cs

@@ -0,0 +1,124 @@
+using System.Drawing;
+using System.Windows.Forms;
+
+namespace OpenNest.Forms;
+
+partial class PostVerificationForm
+{
+    private System.ComponentModel.IContainer components = null;
+    private TableLayoutPanel layout;
+    private Label summaryLabel;
+    private TextBox reportBox;
+    private CheckBox acknowledgeBox;
+    private FlowLayoutPanel buttons;
+    private Button postButton;
+    private Button cancelButton;
+    private bool disposedResources;
+
+    protected override void Dispose(bool disposing)
+    {
+        if (disposing && !disposedResources)
+        {
+            disposedResources = true;
+            cancellation.Cancel();
+            cancellation.Dispose();
+            components?.Dispose();
+        }
+        base.Dispose(disposing);
+    }
+
+    private void InitializeComponent()
+    {
+        layout = new TableLayoutPanel();
+        summaryLabel = new Label();
+        reportBox = new TextBox();
+        acknowledgeBox = new CheckBox();
+        buttons = new FlowLayoutPanel();
+        postButton = new Button();
+        cancelButton = new Button();
+        layout.SuspendLayout();
+        buttons.SuspendLayout();
+        SuspendLayout();
+
+        layout.ColumnCount = 1;
+        layout.ColumnStyles.Add(new ColumnStyle(SizeType.Percent, 100F));
+        layout.RowCount = 4;
+        layout.RowStyles.Add(new RowStyle(SizeType.AutoSize));
+        layout.RowStyles.Add(new RowStyle(SizeType.Percent, 100F));
+        layout.RowStyles.Add(new RowStyle(SizeType.AutoSize));
+        layout.RowStyles.Add(new RowStyle(SizeType.AutoSize));
+        layout.Dock = DockStyle.Fill;
+        layout.Padding = new Padding(12);
+        layout.Controls.Add(summaryLabel, 0, 0);
+        layout.Controls.Add(reportBox, 0, 1);
+        layout.Controls.Add(acknowledgeBox, 0, 2);
+        layout.Controls.Add(buttons, 0, 3);
+
+        summaryLabel.Name = "summaryLabel";
+        summaryLabel.AutoSize = true;
+        summaryLabel.Dock = DockStyle.Fill;
+        summaryLabel.Margin = new Padding(3, 3, 3, 10);
+        summaryLabel.Text = "Checking all plates: overlaps, missing lead-ins, and rapid crossings...";
+        summaryLabel.TabIndex = 0;
+
+        reportBox.Name = "reportBox";
+        reportBox.Dock = DockStyle.Fill;
+        reportBox.Multiline = true;
+        reportBox.ReadOnly = true;
+        reportBox.ScrollBars = ScrollBars.Vertical;
+        reportBox.WordWrap = true;
+        reportBox.MaxLength = 0;
+        reportBox.TabIndex = 1;
+        reportBox.AccessibleName = "Pre-post verification findings";
+        reportBox.Text = "Verification is running. No CNC output has been written.";
+
+        acknowledgeBox.Name = "acknowledgeBox";
+        acknowledgeBox.AutoSize = true;
+        acknowledgeBox.Dock = DockStyle.Fill;
+        acknowledgeBox.Margin = new Padding(3, 12, 3, 12);
+        acknowledgeBox.Enabled = false;
+        acknowledgeBox.Checked = false;
+        acknowledgeBox.Text = "I understand the listed risks, including possible head crashes and machine or material damage.\r\nI choose to bypass these warnings and continue posting this nest.";
+        acknowledgeBox.TabIndex = 2;
+        acknowledgeBox.CheckedChanged += AcknowledgeBox_CheckedChanged;
+
+        buttons.Dock = DockStyle.Fill;
+        buttons.AutoSize = true;
+        buttons.FlowDirection = FlowDirection.RightToLeft;
+        buttons.Controls.Add(cancelButton);
+        buttons.Controls.Add(postButton);
+        buttons.TabIndex = 3;
+
+        cancelButton.Name = "cancelButton";
+        cancelButton.Text = "Cancel";
+        cancelButton.AutoSize = true;
+        cancelButton.DialogResult = DialogResult.Cancel;
+        cancelButton.TabIndex = 0;
+
+        postButton.Name = "postButton";
+        postButton.Text = "Continue Posting";
+        postButton.AutoSize = true;
+        postButton.Enabled = false;
+        postButton.TabIndex = 1;
+        postButton.Click += PostButton_Click;
+
+        AcceptButton = cancelButton;
+        CancelButton = cancelButton;
+        AutoScaleDimensions = new SizeF(7F, 15F);
+        AutoScaleMode = AutoScaleMode.Font;
+        ClientSize = new Size(850, 560);
+        MinimumSize = new Size(700, 440);
+        Controls.Add(layout);
+        MaximizeBox = false;
+        MinimizeBox = false;
+        Name = "PostVerificationForm";
+        ShowInTaskbar = false;
+        StartPosition = FormStartPosition.CenterParent;
+        Text = "Verify Nest Before Posting";
+        layout.ResumeLayout(false);
+        layout.PerformLayout();
+        buttons.ResumeLayout(false);
+        buttons.PerformLayout();
+        ResumeLayout(false);
+    }
+}

OpenNest/Forms/PostVerificationForm.cs

@@ -0,0 +1,122 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using System.Windows.Forms;
+using OpenNest.Diagnostics;
+
+namespace OpenNest.Forms;
+
+/// <summary>
+/// One posting attempt. The owner must prevent background nest edits before opening
+/// this modal form; cancellation keeps it modal until the read-only worker stops.
+/// </summary>
+public partial class PostVerificationForm : Form
+{
+    private readonly Nest nest;
+    private readonly Func<Nest, CancellationToken, Task<PostVerificationReport>> analyze;
+    private readonly CancellationTokenSource cancellation = new();
+    private PostVerificationReport report;
+    private bool started;
+    private bool analyzing;
+    private bool closeRequested;
+
+    public PostVerificationForm(Nest nest, IPostProcessor postProcessor = null)
+        : this(nest, (value, token) => Task.Run(
+            () => PostVerificationAnalyzer.AnalyzeForPost(value, postProcessor, token), token))
+    { }
+
+    internal PostVerificationForm(Nest nest,
+        Func<Nest, CancellationToken, Task<PostVerificationReport>> analyze)
+    {
+        this.nest = nest ?? throw new ArgumentNullException(nameof(nest));
+        this.analyze = analyze ?? throw new ArgumentNullException(nameof(analyze));
+        InitializeComponent();
+    }
+
+    protected override async void OnShown(EventArgs e)
+    {
+        base.OnShown(e);
+        await VerifyAsync();
+    }
+
+    internal async Task VerifyAsync()
+    {
+        if (started)
+            return;
+        started = true;
+        analyzing = true;
+        try
+        {
+            var result = await analyze(nest, cancellation.Token);
+            if (closeRequested || IsDisposed)
+                return;
+            report = result;
+            reportBox.Text = report.ToDisplayText();
+            reportBox.SelectionStart = 0;
+            reportBox.SelectionLength = 0;
+            summaryLabel.Text = report.HasWarnings
+                ? "Warnings found. Review every finding before deciding whether to post."
+                : "Verification complete. No warnings found by these checks.";
+            acknowledgeBox.Visible = report.HasWarnings;
+            acknowledgeBox.Enabled = report.HasWarnings;
+            acknowledgeBox.Checked = false;
+            postButton.Text = report.HasWarnings ? "Post Anyway" : "Continue Posting";
+        }
+        catch (OperationCanceledException) when (cancellation.IsCancellationRequested)
+        {
+            closeRequested = true;
+        }
+        catch (Exception ex)
+        {
+            if (!IsDisposed)
+            {
+                report = null;
+                summaryLabel.Text = "Verification failed. Posting is blocked.";
+                reportBox.Text = "The verification could not finish. Cancel, correct the problem, and try again."
+                    + Environment.NewLine + Environment.NewLine + ex.Message;
+            }
+        }
+        finally
+        {
+            analyzing = false;
+            if (!IsDisposed)
+            {
+                UpdatePostPermission();
+                if (closeRequested)
+                {
+                    DialogResult = DialogResult.Cancel;
+                    Close();
+                }
+            }
+        }
+    }
+
+    private void UpdatePostPermission() =>
+        postButton.Enabled = !analyzing && !closeRequested
+            && report?.CanPost(acknowledgeBox.Checked) == true;
+
+    private void AcknowledgeBox_CheckedChanged(object sender, EventArgs e) => UpdatePostPermission();
+
+    private void PostButton_Click(object sender, EventArgs e)
+    {
+        // Check again here; an enabled button alone is not consent enforcement.
+        if (analyzing || closeRequested || report?.CanPost(acknowledgeBox.Checked) != true)
+            return;
+        DialogResult = DialogResult.OK;
+        Close();
+    }
+
+    protected override void OnFormClosing(FormClosingEventArgs e)
+    {
+        if (analyzing)
+        {
+            closeRequested = true;
+            cancellation.Cancel();
+            postButton.Enabled = false;
+            cancelButton.Enabled = false;
+            summaryLabel.Text = "Canceling verification...";
+            e.Cancel = true;
+        }
+        base.OnFormClosing(e);
+    }
+}

Posts/OpenNest.Posts.CincinnatiCIFiber/CIFiberPostProcessor.cs

@@ -18,7 +18,8 @@ namespace OpenNest.Posts.CincinnatiCIFiber
     /// </summary>
     public sealed class CIFiberPostProcessor
         : IConfigurablePostProcessor,
-            IMultiFilePostProcessor
+            IMultiFilePostProcessor,
+            IPostVerificationSupport
     {
         private static readonly JsonSerializerOptions JsonOptions = new()
         {
@@ -27,6 +28,7 @@ namespace OpenNest.Posts.CincinnatiCIFiber
         };
 
         public string Name => "Cincinnati CI Fiber";
+        public bool PreservesPlacedProgramOrder => true;
         public string Author => "OpenNest";
         public string Description =>
             "CI Fiber family laser (TF5200 / nLight CLX), e.g. CI Fiber 4020 8kW";

README.md

@@ -13,7 +13,7 @@ A Windows desktop application for CNC nesting — imports DXF drawings, arranges
 - **Nesting** — pluggable whole-job engines (Default, Strip, Vertical/Horizontal Remnant, StockLadder, plus DLL plugins), NFP-based interlocking pair evaluation, gravity compaction, rotation sweeps, multi-plate/multi-material jobs.
 - **Plate operations** — manual sheet cut-offs, [automatic scrap cutoffs with unused-tail preservation](docs/automatic-scrap-cutoffs.md), oversized-part splitting (straight, weld-gap tabs, spike-groove), interactive editing, and spacing-aware pushes that can slide along or away from touching parts.
 - **Visual overlap check** — manually highlight shared material on the active plate, including containment and cutouts, with area shading, pair centroids, and hover details through View > Overlap Check. [Usage and limitations](docs/geometry/visual-overlap-check.md).
-- **CNC output** — configurable lead-ins/outs and tabs, contour editing, user-defined G-code variables (`$name` → `#200+` machine variables), plugin post-processors (Cincinnati CL-707/800/900/940/CLX included).
+- **CNC output** — configurable lead-ins/outs and tabs, contour editing, user-defined G-code variables (`$name` → `#200+` machine variables), plugin post-processors (Cincinnati CL-707/800/900/940/CLX included). [Pre-post verification](docs/post-verification.md) checks overlaps, missing lead-ins, and rapid crossings, with explicit risk acknowledgment required to bypass warnings.
 
 ## Requirements
 

docs/post-verification.md

@@ -0,0 +1,112 @@
+# Verify a nest before posting
+
+The desktop's **Nest > Post > (post processor)** workflow checks every plate after
+post settings are accepted and before asking where to save CNC output. The review
+shows all three check categories, even when there are no findings:
+
+- **Overlapping parts:** shared material between placed parts, including containment.
+  Holes are subtracted; placing a part inside a sufficiently large cutout is not
+  itself an overlap. This uses clean drawing geometry, not added lead-in/out paths.
+- **Missing lead-ins:** cutting contours without an actual, nonzero lead-in in the
+  placed program. Applying a lead-in to only one contour does not clear the other
+  contours. Scribe-only work and scrap cutoff lines do not require lead-ins here.
+- **Rapid crossings:** direct XY moves crossing closed, already-cut, untabbed
+  contours in cutting order. This includes earlier holes within the same part and
+  previously cut parts. A future cut is not an obstacle yet. Actual uncut gaps are
+  respected; enabling tabs in settings alone is not evidence that a gap exists.
+
+Findings identify the plate and part's position in the cutting sequence. Read the
+scrollable report, cancel to fix the nest, then post again to rerun verification.
+Uncheckable geometry is reported as incomplete, not passed. Multiple interrupted
+cut fragments, or a lead-out after an open contour that might cut through a tab,
+also require manual review rather than being assumed retained.
+
+## Explicit override
+
+With any warning, **Post Anyway** is disabled until the user selects:
+
+> I understand the listed risks, including possible head crashes and machine or
+> material damage. I choose to bypass these warnings and continue posting this nest.
+
+Consent applies only to that posting attempt. Unchecking disables posting again;
+opening another review always starts unchecked. Cancel, Escape, and the window's
+close button do not write CNC files. Cancel is the default button. A clear report
+still requires **Continue Posting**. An unexpected verification failure blocks
+posting rather than allowing an override of an absent report.
+
+The editor is modal during verification and posting dialogs. Posting is refused
+while auto-nesting, interactive fill, or a busy plate action can still change the
+nest. Cancellation keeps the modal dialog open until its worker has stopped.
+No automatic repair, resequencing, lead-in insertion, or tab insertion is performed.
+
+## Console
+
+`--post` prints the same report. Warnings prevent CNC output (including overwriting
+an existing file) and return exit code 1. After reviewing them, explicitly pass
+`--acknowledge-post-risks` to accept the risks for that invocation. The switch does
+not skip verification and is not persisted. When `--post` is requested, verification
+must pass or be acknowledged before either nest saving or CNC writing. Nest-save
+and CNC destinations must differ; collisions are refused even with acknowledgment.
+Without `--post`, ordinary nest saving is unchanged; `--no-save` skips that save.
+
+The raw `IPostProcessor` plugin interface remains a low-level writer. Third-party
+callers must apply their own review/consent flow using `PostVerificationAnalyzer`;
+the gate is installed at OpenNest's desktop and console posting entry points.
+
+## Selected post and cut order
+
+Cincinnati CI Fiber preserves the placed part/contour order and pierce positions
+used by this check. The older Cincinnati CL post sorts parts and moves cutoffs;
+Gravograph builds and optimizes separate tool passes. Those two posts, and unknown
+plugins, therefore show an additional **incomplete final rapid sequence** warning
+requiring acknowledgment even if the nest-level checks have no findings. This
+change does not silently alter their existing CNC output order.
+
+## Limits and maintainer contract
+
+These checks are warnings, not a machine safety certification. They inspect the
+nest's placed programs and direct XY travel, not a simulation of final NC output.
+A post processor or controller may change routing, cutting order, lead-ins,
+retract height, or parking moves. The checks do not model tipping, slats, clamps,
+actual tab strength, kerf, or safe Z height. Review the generated CNC program and
+machine setup before cutting, even when this report has no warnings.
+
+`OpenNest.Core/Diagnostics/PostVerificationAnalyzer` owns the cross-platform logic;
+its report exposes findings, display text, and `CanPost(risksAcknowledged)`. Use
+`AnalyzeForPost` at posting entry points so unknown post ordering is not silently
+certified. `IPostVerificationSupport.PreservesPlacedProgramOrder` is an opt-in
+contract, not a machine-safety claim; only declare it after verifying the writer's
+part order, contour order, and pierce positions. The WinForms dialog renders the
+report and enforces per-attempt consent. New callers
+must keep inputs stable until analysis completes, honor cancellation, and never
+treat incomplete analysis as a clear result. Keep analysis out of paint handlers.
+The overlap diagnostic's documented numeric/tessellation limits also apply.
+
+Future hardening should inspect a shared post-specific emitted motion stream,
+including controller retracts and final parking, rather than pretending direct XY
+geometry proves physical head clearance.
+
+## Verification on Windows
+
+The core/console tests run cross-platform. Dialog tests and actual desktop behavior
+require Windows; Linux cross-compilation is not runtime verification.
+
+1. Run `dotnet test OpenNest.WinForms.Tests/OpenNest.WinForms.Tests.csproj`.
+2. Post a nest containing two overlapping parts and a part without lead-ins.
+   Verify the report lists the plates/parts, shows all check categories, and disables
+   **Post Anyway** until consent is checked. Uncheck it to verify disabling again.
+3. Cancel with the button, Escape, and X on separate attempts; none should open the
+   output save dialog. Reopen the review and confirm consent is reset.
+4. Use a sequence that cuts a closed untabbed part, moves to its far side, then
+   rapids back across it. Verify a crossing warning. Change the sequence so the
+   perimeter has not yet been cut, then assign a real tab gap and recheck the
+   appropriate control cases. Include a hole crossed later in the same part.
+5. Acknowledge the warnings and post through both a single-file and multi-file post.
+   Confirm output and normal overwrite prompts. Post a clear, leaded nest with Cincinnati CI Fiber and
+   verify the report still appears without requiring a risk override.
+6. During a large verification, cancel; the editor must stay disabled until the
+   worker exits, with no output. A fill still finishing after its progress dialog
+   closes must prevent posting until it has completed.
+
+For failures, record the menu action, nest fixture, selected post, visible report,
+and exact exception text.