fix(template-engine): resolve TemplateEngine-011,013,014 — remove dead converter, duplicate-id-safe cycle detection, unified deletion logic; TemplateEngine-012 deferred

src/ScadaLink.TemplateEngine/Flattening/RevisionHashService.cs

@@ -8,19 +8,24 @@ namespace ScadaLink.TemplateEngine.Flattening;
 
 /// <summary>
 /// Produces a deterministic SHA-256 hash of a FlattenedConfiguration.
-/// Same content always produces the same hash across runs by using
-/// canonical JSON serialization with sorted keys.
+/// Same content always produces the same hash across runs.
+/// <para>
+/// DETERMINISM CONTRACT: System.Text.Json serializes properties in CLR
+/// declaration order, which it does NOT sort. Stable output therefore relies
+/// on the private <c>Hashable*</c> records below declaring their properties
+/// in alphabetical order. A contributor adding a property out of alphabetical
+/// order would silently change every revision hash; the ordering is guarded
+/// by <c>RevisionHashServiceTests.HashableRecords_PropertiesDeclaredAlphabetically</c>.
+/// Collections are explicitly sorted by <c>CanonicalName</c> before hashing.
+/// </para>
 /// </summary>
 public class RevisionHashService
 {
     private static readonly JsonSerializerOptions CanonicalJsonOptions = new()
     {
-        // Sort properties alphabetically for determinism
         PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
         DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
-        WriteIndented = false,
-        // Ensure consistent ordering
-        Converters = { new SortedPropertiesConverterFactory() }
+        WriteIndented = false
     };
 
     /// <summary>
@@ -84,7 +89,9 @@ public class RevisionHashService
         return $"sha256:{Convert.ToHexStringLower(hashBytes)}";
     }
 
-    // Internal types for deterministic serialization (sorted property names via camelCase + alphabetical)
+    // Internal types for deterministic serialization. Properties MUST be declared
+    // in alphabetical order — System.Text.Json emits them in declaration order and
+    // does not sort. See the DETERMINISM CONTRACT note on the class summary.
     private sealed record HashableConfiguration
     {
         public List<HashableAlarm> Alarms { get; init; } = [];
@@ -128,14 +135,3 @@ public class RevisionHashService
         public string? TriggerType { get; init; }
     }
 }
-
-/// <summary>
-/// A JSON converter factory that ensures properties are serialized in alphabetical order
-/// for deterministic output. Works with record types.
-/// </summary>
-internal class SortedPropertiesConverterFactory : JsonConverterFactory
-{
-    public override bool CanConvert(Type typeToConvert) => false;
-
-    public override JsonConverter? CreateConverter(Type typeToConvert, JsonSerializerOptions options) => null;
-}