feat: add Disable/Enable API to FillStrategyRegistry

Adds methods to permanently disable/enable strategies by name. Disabled
strategies remain registered but are excluded from the default pipeline.
SetEnabled (used for remnant fills) takes precedence over the disabled
set, so explicit overrides still work.

Pipeline test now checks against active strategy count dynamically.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Engine/Strategies/FillStrategyRegistry.cs

@@ -12,6 +12,7 @@ namespace OpenNest.Engine.Strategies
         private static readonly List<IFillStrategy> strategies = new();
         private static List<IFillStrategy> sorted;
         private static HashSet<string> enabledFilter;
+        private static readonly HashSet<string> disabled = new(StringComparer.OrdinalIgnoreCase);
 
         static FillStrategyRegistry()
         {
@@ -19,9 +20,36 @@ namespace OpenNest.Engine.Strategies
         }
 
         public static IReadOnlyList<IFillStrategy> Strategies =>
-            sorted ??= (enabledFilter != null
-                ? strategies.Where(s => enabledFilter.Contains(s.Name)).OrderBy(s => s.Order).ToList()
-                : strategies.OrderBy(s => s.Order).ToList());
+            sorted ??= FilterStrategies();
+
+        private static List<IFillStrategy> FilterStrategies()
+        {
+            var source = enabledFilter != null
+                ? strategies.Where(s => enabledFilter.Contains(s.Name))
+                : strategies.Where(s => !disabled.Contains(s.Name));
+            return source.OrderBy(s => s.Order).ToList();
+        }
+
+        /// <summary>
+        /// Permanently disables strategies by name. They remain registered
+        /// but are excluded from the default pipeline.
+        /// </summary>
+        public static void Disable(params string[] names)
+        {
+            foreach (var name in names)
+                disabled.Add(name);
+            sorted = null;
+        }
+
+        /// <summary>
+        /// Re-enables a previously disabled strategy.
+        /// </summary>
+        public static void Enable(params string[] names)
+        {
+            foreach (var name in names)
+                disabled.Remove(name);
+            sorted = null;
+        }
 
         /// <summary>
         /// Restricts the active strategies to only those whose names are listed.

OpenNest.Tests/Strategies/FillPipelineTests.cs

@@ -1,3 +1,4 @@
+using OpenNest.Engine.Strategies;
 using OpenNest.Geometry;
 
 namespace OpenNest.Tests.Strategies;
@@ -24,8 +25,8 @@ public class FillPipelineTests
 
         engine.Fill(item, plate.WorkArea(), null, System.Threading.CancellationToken.None);
 
-        Assert.True(engine.PhaseResults.Count >= 6,
-            $"Expected phase results from all strategies, got {engine.PhaseResults.Count}");
+        Assert.True(engine.PhaseResults.Count >= FillStrategyRegistry.Strategies.Count,
+            $"Expected phase results from all active strategies, got {engine.PhaseResults.Count}");
     }
 
     [Fact]