- Add detect_inheritance_cycles() function to _resource_type_validation.py
- Function detects both direct self-inheritance (A→A) and multi-level cycles (A→B→A, A→B→C→A)
- Add BDD tests for cycle detection scenarios
- Tests cover direct self-inheritance, two-level cycles, three-level cycles, and valid chains

@@ -0,0 +52,4 @@
+        # Perform multi-level cycle detection using the registry first.
+        # This mirrors what a registry-aware service would do before
+        # persisting a new type definition.
+        detect_inheritance_cycles(name, parent, registry if registry else None)

@@ -276,0 +305,4 @@
+        visited: set[str] = {name}
+        current = inherits
+
+        while current is not None:

@@ -342,2 +344,2 @@
-        if self.inherits is not None and self.inherits == self.name:
-            raise ValueError(f"'{self.name}' cannot inherit from itself.")
+        # ADR-042 rule 3: no cycles (self-inheritance and multi-level cycles)
+        _detect_inheritance_cycles(self.name, self.inherits)