fix(diagnostics): report parts covering a tiny clamp in the overlap check

Collision.Check finds no overlap region for a clamp smaller than its
tolerance, so Check Overlaps reported a part covering a 1e-5 clamp as clear.
Clamps below 0.001 are judged with KeepOutOverlap and reported as a finding
whose fragment is the whole clamp rectangle; flush and clear parts stay clear.

PM aa995123-295f-479c-adc4-b0cbcb7cf838

OpenNest.Core/Diagnostics/PlateOverlapAnalyzer.cs

@@ -275,6 +275,15 @@ public static class PlateOverlapAnalyzer
                     continue;
                 try
                 {
+                    // A clamp below the polygon tolerance collapses in Collision.Check and would
+                    // read as clear (PM aa995123): judge it tolerance-free and report the whole
+                    // (negligibly small) clamp rectangle as the overlap fragment.
+                    if (KeepOutOverlap.NeedsToleranceFreeTest(zone))
+                    {
+                        if (KeepOutOverlap.MaterialEnters(part.Material.Outer, part.Material.Holes, zone))
+                            findings.Add(TinyClampFinding(part, clamp));
+                        continue;
+                    }
                     var origin = part.Material.Outer.Vertices[0];
                     var local = part.Material.Transform(0, origin * -1);
                     var rect = RectanglePolygon(zone, origin * -1);
@@ -311,6 +320,19 @@ public static class PlateOverlapAnalyzer
         return findings;
     }
 
+    private static PlateOverlapPair TinyClampFinding(PreparedPart part, CapturedClamp clamp)
+    {
+        var zone = clamp.Bounds;
+        var corners = new[]
+        {
+            new Vector(zone.Left, zone.Bottom), new Vector(zone.Right, zone.Bottom),
+            new Vector(zone.Right, zone.Top), new Vector(zone.Left, zone.Top),
+        };
+        var centre = new Vector((zone.Left + zone.Right) / 2, (zone.Bottom + zone.Top) / 2);
+        return new PlateOverlapPair(part.Input.Id, ClampFindingSlot.IdFor(clamp.Ordinal), part.Input.Name,
+            $"Clamp '{clamp.Id}'", new List<PlateOverlapRegion> { new(corners, zone.Length * zone.Width) }, centre);
+    }
+
     private static Polygon RectanglePolygon(Box box, Vector offset)
     {
         var polygon = new Polygon();

OpenNest.Tests/Diagnostics/PlateOverlapAnalyzerClampZoneTests.cs

@@ -196,6 +196,24 @@ public class PlateOverlapAnalyzerClampZoneTests
         Assert.NotEqual(OverlapCheckStatus.Current, state.Status);
     }
 
+    // C16 (PM 6859db53): a 1e-5 square zone, far below the outline tolerance. A part covering
+    // it is still reported (never silently clear); flush or clear parts are not.
+    [Theory]
+    [InlineData(7.5, true)]
+    [InlineData(6.0, false)]
+    [InlineData(8.00001, false)]
+    [InlineData(3.0, false)]
+    public void TinyClampZoneIsJudgedWithoutOutlineCollapse(double x, bool overlaps)
+    {
+        var tiny = new ClampZone("tiny", new Box(8, 0, 1e-5, 1e-5));
+        var parts = new List<Part> { new(Square("p", 2), new Vector(x, 0)) };
+
+        var report = PlateOverlapAnalyzer.Analyze(PlateOverlapAnalyzer.Capture(parts, new[] { tiny }));
+
+        Assert.True(report.IsComplete, string.Join("; ", report.Issues.Select(issue => issue.Message)));
+        Assert.Equal(overlaps, report.ClampFindings.Any(f => f.PartBName.Contains("tiny")));
+    }
+
     private static string Describe(PlateOverlapReport report) =>
         string.Join(";", report.Pairs.Select(p => $"{p.PartAId}/{p.PartBId}:{p.Area:R}"))
         + "|"