fix(diagnostics): read absolute subprogram holes and refuse unknown codes

PlateOverlapAnalyzer converted clean programs directly with
ConvertProgram.ToGeometry, which adds call offsets only to
incremental moves, so holes in absolute-mode subprograms were read at
their frame origin. A square with two absolute holes reported
"Native material contours cross or touch", and the Plan Cutting
overlap gate blocked it while the incremental twin passed. Convert an
owned incremental-mode copy instead (PreparedContours.CopyForGeometry,
now internal, the same normalization the cutting planner uses).

The analyzer also threw on a program whose Codes list was null and
cast or cloned instructions it does not know. It now refuses a
missing list and anything other than the exact built-in instruction
types as an incomplete check, before any copy or conversion runs.
Pre-post verification and the plate overlap overlay share this path.

OpenNest.Core/Diagnostics/OverlapMaterialCache.cs

@@ -43,7 +43,7 @@ internal sealed class OverlapSource
 
     internal OverlapSource(Program program, List<Entity> entities, string error)
     {
-        codeCount = program.Codes.Count;
+        codeCount = CodeCount(program);
         rotation = BitConverter.DoubleToInt64Bits(program.Rotation);
         Entities = entities;
         Error = error;
@@ -54,7 +54,10 @@ internal sealed class OverlapSource
     internal string Error { get; }
 
     internal bool Matches(Program program) =>
-        program.Codes.Count == codeCount && BitConverter.DoubleToInt64Bits(program.Rotation) == rotation;
+        CodeCount(program) == codeCount && BitConverter.DoubleToInt64Bits(program.Rotation) == rotation;
+
+    // Program.Codes is a writable field; a missing list is a refused source, not a crash.
+    private static int CodeCount(Program program) => program.Codes?.Count ?? -1;
 
     /// <summary>
     /// Prepares once and shares the result. A geometry failure is cached like a success;