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

tests/ScadaLink.TemplateEngine.Tests/CycleDetectorTests.cs

@@ -153,4 +153,77 @@ public class CycleDetectorTests
 
         Assert.Null(result);
     }
+
+    // ========================================================================
+    // TemplateEngine-013: robustness against duplicate Ids and Id 0
+    // ========================================================================
+
+    [Fact]
+    public void DetectInheritanceCycle_DuplicateIdsInList_DoesNotThrow()
+    {
+        // Two not-yet-saved templates both carry Id == 0. ToDictionary(t => t.Id)
+        // would throw ArgumentException; the detector must tolerate it.
+        var templateA = new Template("A") { Id = 0 };
+        var templateB = new Template("B") { Id = 0 };
+        var saved = new Template("Saved") { Id = 1 };
+        var all = new List<Template> { templateA, templateB, saved };
+
+        var ex = Record.Exception(() => CycleDetector.DetectInheritanceCycle(1, 0, all));
+
+        Assert.Null(ex);
+    }
+
+    [Fact]
+    public void DetectCompositionCycle_DuplicateIdsInList_DoesNotThrow()
+    {
+        var templateA = new Template("A") { Id = 0 };
+        var templateB = new Template("B") { Id = 0 };
+        var all = new List<Template> { templateA, templateB };
+
+        var ex = Record.Exception(() => CycleDetector.DetectCompositionCycle(1, 2, all));
+
+        Assert.Null(ex);
+    }
+
+    [Fact]
+    public void DetectCrossGraphCycle_DuplicateIdsInList_DoesNotThrow()
+    {
+        var templateA = new Template("A") { Id = 0 };
+        var templateB = new Template("B") { Id = 0 };
+        var all = new List<Template> { templateA, templateB };
+
+        var ex = Record.Exception(() => CycleDetector.DetectCrossGraphCycle(5, 1, 2, all));
+
+        Assert.Null(ex);
+    }
+
+    [Fact]
+    public void DetectInheritanceCycle_RealIdZero_StillDetectsCycle()
+    {
+        // A template legitimately stored with Id 0 (in-memory / test scenario):
+        // a self-inheritance attempt must still be detected, not skipped as
+        // "no parent" by a 0-as-sentinel overload.
+        var template = new Template("Zero") { Id = 0 };
+        var all = new List<Template> { template };
+
+        var result = CycleDetector.DetectInheritanceCycle(0, 0, all);
+
+        Assert.NotNull(result);
+        Assert.Contains("itself", result);
+    }
+
+    [Fact]
+    public void DetectInheritanceCycle_ParentChainThroughIdZero_DetectsCycle()
+    {
+        // Child(1) -> parent Zero(0) -> parent Child(1): a cycle running through
+        // a template whose real Id is 0 must be detected, not silently skipped.
+        var zero = new Template("Zero") { Id = 0, ParentTemplateId = 1 };
+        var child = new Template("Child") { Id = 1, ParentTemplateId = null };
+        var all = new List<Template> { zero, child };
+
+        var result = CycleDetector.DetectInheritanceCycle(1, 0, all);
+
+        Assert.NotNull(result);
+        Assert.Contains("cycle", result, StringComparison.OrdinalIgnoreCase);
+    }
 }