fix(io): keep a sheet's own clamp rail and its removals through save and reload

Commit can attach the stock's rail to a sheet whose nest has no (or another)
default rail, but only the default rail was saved and the reader re-attached
sheets only to it, so the removed clamp and its time vanished on reload. A
sheet following a rail other than the default now saves it in an optional
per-plate clampRail (read leniently, omitted otherwise), and the reader
re-attaches the sheet to it.

PM 22daec3d-dabb-4aae-95f7-c1d090d5dcdf

OpenNest.IO.Tests/ClampRailPersistenceTests.cs

@@ -424,6 +424,32 @@ public class ClampRailPersistenceTests
         Assert.Contains("\"removedClamps\"", ReadNestJson(RemovedClamp3Nest()), StringComparison.Ordinal);
     }
 
+    // PM 22daec3d: a sheet following a rail other than the nest default keeps its rail,
+    // removed clamps and removal time through save/reload.
+    [Fact]
+    public void SheetRailDifferentFromTheDefaultsSurvivesReload()
+    {
+        var nest = new Nest("no-default-rail");
+        nest.PlateDefaults.Size = new Size(48, 120);
+        var plate = nest.CreatePlate();
+        plate.SetClampRail(Machine(), new[] { "clamp-3" });
+
+        var reopened = Assert.Single(RoundTrip(nest).Plates);
+
+        Assert.Equal(Machine(), reopened.ClampRail);
+        Assert.Equal(new[] { "clamp-3" }, reopened.RemovedClamps);
+        Assert.Equal(ClampRail.DefaultRemovalMinutes, reopened.ClampRemovalMinutes);
+        Assert.Null(RoundTrip(nest).PlateDefaults.ClampRail);
+    }
+
+    [Fact]
+    public void SheetsFollowingTheDefaultRailWriteNoPerSheetRail()
+    {
+        var json = ReadNestJson(RemovedClamp3Nest());
+        var root = JsonNode.Parse(json)!;
+        Assert.Null(root["plates"]![0]!["clampRail"]);
+    }
+
     /// <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

@@ -214,6 +214,15 @@ namespace OpenNest.IO
             [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
             [JsonConverter(typeof(LenientStringListConverter))]
             public List<string> RemovedClamps { get; init; } = new();
+
+            /// <summary>
+            /// The machine clamp rail this sheet follows, written only when it is not the
+            /// nest's default rail (otherwise the sheet re-attaches to that one on load).
+            /// Read leniently like <see cref="PlateDefaultsDto.ClampRail"/>.
+            /// </summary>
+            [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+            [JsonConverter(typeof(LenientClampRailConverter))]
+            public ClampRailDto ClampRail { get; init; }
         }
 
         public record ClampZoneDto

OpenNest.IO/NestReader.cs

@@ -452,8 +452,10 @@ namespace OpenNest.IO
                     .Where(id => !string.IsNullOrEmpty(id))
                     .ToHashSet(StringComparer.Ordinal)
                     ?? new HashSet<string>();
-                if (clampRail != null && clampRail.Matches(plate, removedClamps))
-                    plate.SetClampRail(clampRail, removedClamps);
+                // A sheet saved with its own rail (not the nest default) follows that one.
+                var plateRail = ReadClampRail(p.ClampRail) ?? clampRail;
+                if (plateRail != null && plateRail.Matches(plate, removedClamps))
+                    plate.SetClampRail(plateRail, removedClamps);
 
                 for (var partIndex = 0; partIndex < p.Parts.Count; partIndex++)
                 {

OpenNest.IO/NestWriter.cs

@@ -135,15 +135,7 @@ namespace OpenNest.IO
                     Right = pd.EdgeSpacing.Right,
                     Bottom = pd.EdgeSpacing.Bottom,
                 },
-                ClampRail = pd.ClampRail == null
-                    ? null
-                    : new ClampRailDto
-                    {
-                        Width = pd.ClampRail.Width,
-                        Depth = pd.ClampRail.Depth,
-                        Centers = pd.ClampRail.Centers.ToList(),
-                        RemovalMinutes = pd.ClampRail.RemovalMinutes,
-                    },
+                ClampRail = ToDto(pd.ClampRail),
             };
         }
 
@@ -222,6 +214,17 @@ namespace OpenNest.IO
                 && rail.Matches(plate);
         }
 
+        private static ClampRailDto ToDto(ClampRail rail) =>
+            rail == null
+                ? null
+                : new ClampRailDto
+                {
+                    Width = rail.Width,
+                    Depth = rail.Depth,
+                    Centers = rail.Centers.ToList(),
+                    RemovalMinutes = rail.RemovalMinutes,
+                };
+
         /// <summary>Numeric suffix of a rail clamp id ("clamp-3" -&gt; 3), for a natural sort of
         /// <see cref="PlateDto.RemovedClamps"/> instead of lexical ("clamp-10" before "clamp-2").
         /// A non-matching id sorts last by its own ordinal text.</summary>
@@ -343,6 +346,10 @@ namespace OpenNest.IO
                                 .OrderBy(ClampIndex)
                                 .ThenBy(id => id, StringComparer.Ordinal)
                                 .ToList(),
+                        // Only a rail other than the nest default needs saving per sheet.
+                        ClampRail = Equals(plate.ClampRail, nest.PlateDefaults.ClampRail)
+                            ? null
+                            : ToDto(plate.ClampRail),
                     }
                 );
             }

docs/nest-file-format.md

@@ -86,7 +86,9 @@ Auto Nest removed clamps as a last resort lists their rail ids in an optional
 `removedClamps` array (omitted when none were removed); its `clamps` already
 exclude them, and it follows the rail minus those ids. A malformed
 `removedClamps` value reads as none removed (non-string entries are skipped);
-the saved `clamps` load either way.
+the saved `clamps` load either way. A plate that follows a rail other than the nest's default
+saves it in its own optional `clampRail` (same shape), so its removal state and
+time survive a reload; plates following the default rail omit it.
 
 An empty plate (no parts, no cut-offs) is omitted from the file unless that
 would lose clamp zones: it is omitted like any other empty plate only when a