fix(io): read a malformed removedClamps value without failing the nest

The optional per-plate removedClamps list was deserialized as a typed
List<string>, so a string or a list of numbers threw JsonException and the
whole nest failed to open. It now reads leniently: a non-array value reads
as none removed and non-string entries are skipped. The saved zones load
either way, so a removed clamp's area is never silently re-blocked or lost.

PM 9f3d676b-8a1c-4d9a-b877-b5e01e70c3f0

OpenNest.IO.Tests/ClampRailPersistenceTests.cs

@@ -246,6 +246,46 @@ public class ClampRailPersistenceTests
         Assert.Equal(7, plate.ClampZones.Count);
     }
 
+    // Slice 6 task 6.4 (Slice 3b quality review): optional removal fields read leniently
+    // and are only written when there is something to say.
+
+    private static MemoryStream RemovedClamp3Nest()
+    {
+        var nest = new Nest("railed");
+        nest.PlateDefaults.Size = new Size(48, 120);
+        nest.SetClampRail(Machine());
+        var plate = nest.CreatePlate();
+        plate.SetClampRail(Machine(), new[] { "clamp-3" });
+        return Write(nest);
+    }
+
+    private static MemoryStream WithPlateProperty(MemoryStream file, string name, string json) =>
+        RewriteNestJson(file, text =>
+        {
+            var root = JsonNode.Parse(text)!;
+            root["plates"]![0]![name] = JsonNode.Parse(json);
+            return root.ToJsonString();
+        });
+
+    // PM 9f3d676b: a wrongly shaped removedClamps value must not fail the whole nest.
+    [Theory]
+    [InlineData("\"clamp-3\"", false)]
+    [InlineData("[-1]", false)]
+    [InlineData("{\"id\": \"clamp-3\"}", false)]
+    [InlineData("[-1, \"clamp-3\"]", true)]
+    public void MalformedRemovedClampsLoadWithoutFailingTheNest(string value, bool keepsRemoval)
+    {
+        var tampered = WithPlateProperty(RemovedClamp3Nest(), "removedClamps", value);
+
+        var plate = Assert.Single(new NestReader(tampered).Read().Plates);
+
+        // The saved zones always load, so the removed clamp's area is never re-blocked or lost.
+        Assert.Equal(7, plate.ClampZones.Count);
+        Assert.DoesNotContain(plate.ClampZones, z => z.Id == "clamp-3");
+        Assert.Equal(keepsRemoval, plate.RemovedClamps.Contains("clamp-3"));
+        Assert.Equal(keepsRemoval, plate.ClampRail != null);
+    }
+
     /// <summary>Removes a named property wherever it appears in the document, simulating a
     /// key an older writer never emitted. Rebuilds via <see cref="JsonNode"/> so the result
     /// is always valid JSON regardless of whether the property was first, last or only one

OpenNest.IO/NestFormat.cs

@@ -119,6 +119,41 @@ namespace OpenNest.IO
             }
         }
 
+        /// <summary>
+        /// Reads an optional list of strings without failing the nest: a non-array value
+        /// reads as an empty list and non-string entries are skipped.
+        /// </summary>
+        public sealed class LenientStringListConverter : JsonConverter<List<string>>
+        {
+            public override List<string> Read(
+                ref Utf8JsonReader reader,
+                Type typeToConvert,
+                JsonSerializerOptions options
+            )
+            {
+                using var document = JsonDocument.ParseValue(ref reader);
+                var list = new List<string>();
+                if (document.RootElement.ValueKind != JsonValueKind.Array)
+                    return list;
+                foreach (var element in document.RootElement.EnumerateArray())
+                    if (element.ValueKind == JsonValueKind.String)
+                        list.Add(element.GetString());
+                return list;
+            }
+
+            public override void Write(
+                Utf8JsonWriter writer,
+                List<string> value,
+                JsonSerializerOptions options
+            )
+            {
+                writer.WriteStartArray();
+                foreach (var item in value)
+                    writer.WriteStringValue(item);
+                writer.WriteEndArray();
+            }
+        }
+
         public record ClampRailDto
         {
             /// <summary>Clamp extent along the origin-side edge (X).</summary>
@@ -172,8 +207,11 @@ namespace OpenNest.IO
 
             /// <summary>
             /// Rail clamp ids removed from this sheet as a last resort (D8). Missing or empty
-            /// means none were removed; <see cref="Clamps"/> already excludes them.
+            /// means none were removed; <see cref="Clamps"/> already excludes them. Read
+            /// leniently: a wrongly shaped value reads as none removed, non-string entries
+            /// are skipped, and the saved zones load either way.
             /// </summary>
+            [JsonConverter(typeof(LenientStringListConverter))]
             public List<string> RemovedClamps { get; init; } = new();
         }