fix(graph): fix cyclic graph behavior (strands-agents#768)

fix a bug in the Graph multiagent pattern where the reset_on_revisit feature fails to enable cycles and feedback loops. The issue was in the _find_newly_ready_nodes method, which filtered out completed nodes before they could be revisited, making it impossible to implement feedback loops even when reset_on_revisit=True.

---------

Co-authored-by: Murat Kaan Meral <murmeral@amazon.nl>Co-authored-by: Mackenzie Zastrow <zastrowm@users.noreply.github.com>

Author: 2 people

src/strands/multiagent/graph.py

@@ -469,41 +469,32 @@ async def _execute_graph(self) -> None:
             ready_nodes.clear()
 
             # Execute current batch of ready nodes concurrently
-            tasks = [
-                asyncio.create_task(self._execute_node(node))
-                for node in current_batch
-                if node not in self.state.completed_nodes
-            ]
+            tasks = [asyncio.create_task(self._execute_node(node)) for node in current_batch]
 
             for task in tasks:
                 await task
 
             # Find newly ready nodes after batch execution
-            ready_nodes.extend(self._find_newly_ready_nodes())
+            # We add all nodes in current batch as completed batch,
+            # because a failure would throw exception and code would not make it here
+            ready_nodes.extend(self._find_newly_ready_nodes(current_batch))
 
-    def _find_newly_ready_nodes(self) -> list["GraphNode"]:
+    def _find_newly_ready_nodes(self, completed_batch: list["GraphNode"]) -> list["GraphNode"]:
         """Find nodes that became ready after the last execution."""
         newly_ready = []
         for _node_id, node in self.nodes.items():
-            if (
-                node not in self.state.completed_nodes
-                and node not in self.state.failed_nodes
-                and self._is_node_ready_with_conditions(node)
-            ):
+            if self._is_node_ready_with_conditions(node, completed_batch):
                 newly_ready.append(node)
         return newly_ready
 
-    def _is_node_ready_with_conditions(self, node: GraphNode) -> bool:
+    def _is_node_ready_with_conditions(self, node: GraphNode, completed_batch: list["GraphNode"]) -> bool:
         """Check if a node is ready considering conditional edges."""
         # Get incoming edges to this node
         incoming_edges = [edge for edge in self.edges if edge.to_node == node]
 
-        if not incoming_edges:
-            return node in self.entry_points
-
         # Check if at least one incoming edge condition is satisfied
         for edge in incoming_edges:
-            if edge.from_node in self.state.completed_nodes:
+            if edge.from_node in completed_batch:
                 if edge.should_traverse(self.state):
                     logger.debug(
                         "from=<%s>, to=<%s> | edge ready via satisfied condition", edge.from_node.node_id, node.node_id