From 74302761ce2e948448798dd34785351e9ccdcf2f Mon Sep 17 00:00:00 2001
From: AJ Isaacs <ajisaacs27@gmail.com>
Date: Mon, 28 Sep 2026 19:05:03 -0400
Subject: [PATCH] fix(io): restore hole sub-programs with negative IDs

---
 OpenNest.IO/NestReader.cs                     | 12 +++++------
 .../IO/SubProgramSerializationTests.cs        | 21 +++++++++++++++++++
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/OpenNest.IO/NestReader.cs b/OpenNest.IO/NestReader.cs
index b5d4202..dc7174d 100644
--- a/OpenNest.IO/NestReader.cs
+++ b/OpenNest.IO/NestReader.cs
@@ -89,7 +89,7 @@ namespace OpenNest.IO
         private static void ReadSubPrograms(Program parent, Stream stream)
         {
             using var reader = new StreamReader(stream);
-            var currentId = -1;
+            var currentId = (int?)null;
             var lines = new List<string>();
 
             string line;
@@ -100,18 +100,18 @@ namespace OpenNest.IO
                 if (trimmed.StartsWith(":") && int.TryParse(trimmed.Substring(1), out var id))
                 {
                     // Flush previous sub-program
-                    if (currentId >= 0 && lines.Count > 0)
-                        parent.SubPrograms[currentId] = ParseSubProgram(lines);
+                    if (currentId.HasValue && lines.Count > 0)
+                        parent.SubPrograms[currentId.Value] = ParseSubProgram(lines);
 
                     currentId = id;
                     lines.Clear();
                 }
                 else if (trimmed == "M99")
                 {
-                    if (currentId >= 0 && lines.Count > 0)
-                        parent.SubPrograms[currentId] = ParseSubProgram(lines);
+                    if (currentId.HasValue && lines.Count > 0)
+                        parent.SubPrograms[currentId.Value] = ParseSubProgram(lines);
 
-                    currentId = -1;
+                    currentId = null;
                     lines.Clear();
                 }
                 else
diff --git a/OpenNest.Tests/IO/SubProgramSerializationTests.cs b/OpenNest.Tests/IO/SubProgramSerializationTests.cs
index 65679c5..ea8f341 100644
--- a/OpenNest.Tests/IO/SubProgramSerializationTests.cs
+++ b/OpenNest.Tests/IO/SubProgramSerializationTests.cs
@@ -46,6 +46,27 @@ public class SubProgramSerializationTests
         Assert.True(drawing.Program.SubPrograms.ContainsKey(call.Id));
     }
 
+    [Theory]
+    [InlineData(-42)]
+    [InlineData(-1)]
+    public void NegativeSubProgramId_RoundTripsAndBinds(int id)
+    {
+        var nest = CreateNestWithHoleSubProgram();
+        var program = nest.Drawings.First().Program;
+        var sub = program.SubPrograms[42];
+        program.SubPrograms.Clear();
+        program.SubPrograms[id] = sub;
+        program.Codes.OfType<SubProgramCall>().Single().Id = id;
+        using var stream = new MemoryStream();
+        new NestWriter(nest).Write(stream);
+        stream.Position = 0;
+
+        var restored = new NestReader(stream).Read().Drawings.First().Program;
+
+        Assert.True(restored.SubPrograms.ContainsKey(id));
+        Assert.Same(restored.SubPrograms[id], restored.Codes.OfType<SubProgramCall>().Single().Program);
+    }
+
     private static Nest CreateNestWithHoleSubProgram()
     {
         var sub = new Program(Mode.Incremental);