Detect inheritance directives without paths

internal/engine/inheritance_test.go

@@ -121,6 +121,24 @@ func TestSiblingInheritanceRejectsInvalidRelationships(t *testing.T) {
 	}
 }
 
+func TestLoadDetectsInvalidInheritanceInsideSequence(t *testing.T) {
+	input := []byte(`items:
+  - child: {extends: true}
+`)
+	result, err := testLoad[map[string]any](Bytes("nested-inheritance.yml", input), Options[map[string]any]{})
+	if result != nil || err == nil {
+		t.Fatalf("result, err = %#v, %v; want invalid nested inheritance", result, err)
+	}
+	loadError, ok := err.(*LoadError)
+	if !ok {
+		t.Fatalf("error type = %T, want *LoadError", err)
+	}
+	diagnostics := loadError.Diagnostics()
+	if len(diagnostics) != 1 || diagnostics[0].Code != CodeInheritanceInvalid || diagnostics[0].Path.String() != "/items/0/child/extends" {
+		t.Fatalf("diagnostics = %#v", diagnostics)
+	}
+}
+
 func TestSiblingInheritanceDetectsDeepCycleWithoutRecursiveDependencyWalk(t *testing.T) {
 	const count = 2048
 	entries := make([]document.Entry, count)