Fix:
- Read actor_ref from NodeDefinition actor_ref field (not node.config.get)
- Add cross-actor subgraph cycle detection tests (Behave + Robot Framework)
- Apply ruff format to robot/helper_actor_compiler.py to pass CI format check

@@ -377,3 +377,3 @@
 
 
-@given("a config dictionary with 2 custom strategies")
+@given("a actor_refionary with 2 custom strategies")

@@ -227,3 +227,3 @@
 
 
-@then('the config dict should include "{key}"')
+@then('the actor_ref should include "{key}"')

@@ -171,3 +171,3 @@
         configs: dict[str, dict[str, Any]],
     ) -> list[str]:
-        """Register multiple strategies from a config dictionary.
+        """Register multiple strategies from a actor_refionary.

@@ -0,0 +12,4 @@
+
+  Scenario: Mutually-referencing actors raise SubgraphCycleError
+    Given actor "test/actor-a" has a subgraph node with actor_ref "test/actor-b"
+    And actor "test/actor-b" has a subgraph node with actor_ref "test/actor-a"

@@ -0,0 +13,4 @@
+
+from __future__ import annotations
+
+from behave import given, then, when  # type: ignore[import-untyped]

@@ -0,0 +1,35 @@
+Feature: Cross-actor subgraph cycle detection reads actor_ref field

@@ -0,0 +19,4 @@
+from cleveragents.actor.compiler import (
+    SubgraphCycleError,
+    compile_actor,
+)

@@ -0,0 +14,4 @@
+from __future__ import annotations
+
+from behave import given, then, when  # type: ignore[import-untyped]
+from behave.runner import Context  # type: ignore[import-untyped]