fix: find runnable predecessor for every successor that is not runnable (#2996)

* refactor: add find_runnable_predecessors_for_successor method

* feat: refactor find_next_runnable_vertices method

Refactor the `find_next_runnable_vertices` method in the `Graph` class to improve readability and simplify the logic. Instead of using a list comprehension, the method now uses a for loop to iterate over the `vertex_successors_ids` and determine if each vertex is runnable. If a vertex is not runnable, it calls the `find_runnable_predecessors_for_successor` method to find the runnable predecessors. The runnable vertices are then added to the `next_runnable_vertices` list. This refactoring improves the clarity and maintainability of the code.

src/backend/base/langflow/graph/graph/base.py

@@ -992,10 +992,14 @@ class Graph:
         return self
 
     def find_next_runnable_vertices(self, vertex_id: str, vertex_successors_ids: List[str]) -> List[str]:
-        direct_successors_ready = [v_id for v_id in vertex_successors_ids if self.is_vertex_runnable(v_id)]
-        if not direct_successors_ready:
-            return self.find_runnable_predecessors_for_successors(vertex_id)
-        return direct_successors_ready
+        next_runnable_vertices = []
+        for v_id in vertex_successors_ids:
+            if not self.is_vertex_runnable(v_id):
+                next_runnable_vertices.extend(self.find_runnable_predecessors_for_successor(v_id))
+            else:
+                next_runnable_vertices.append(v_id)
+
+        return next_runnable_vertices
 
     async def get_next_runnable_vertices(self, lock: asyncio.Lock, vertex: "Vertex", cache: bool = True) -> List[str]:
         v_id = vertex.id
@@ -1461,6 +1465,13 @@ class Graph:
         This checks the direct predecessors of each successor to identify any that are
         immediately runnable, expanding the search to ensure progress can be made.
         """
+        runnable_vertices = []
+        for successor_id in self.run_manager.run_map.get(vertex_id, []):
+            runnable_vertices.extend(self.find_runnable_predecessors_for_successor(successor_id))
+
+        return runnable_vertices
+
+    def find_runnable_predecessors_for_successor(self, vertex_id: str) -> List[str]:
         runnable_vertices = []
         visited = set()
 
@@ -1476,10 +1487,8 @@ class Graph:
                 for pred_pred_id in self.run_manager.run_predecessors.get(predecessor_id, []):
                     find_runnable_predecessors(self.get_vertex(pred_pred_id))
 
-        for successor_id in self.run_manager.run_map.get(vertex_id, []):
-            for predecessor_id in self.run_manager.run_predecessors.get(successor_id, []):
-                find_runnable_predecessors(self.get_vertex(predecessor_id))
-
+        for predecessor_id in self.run_manager.run_predecessors.get(vertex_id, []):
+            find_runnable_predecessors(self.get_vertex(predecessor_id))
         return runnable_vertices
 
     def remove_from_predecessors(self, vertex_id: str):