feat(dag_engine): implement cascade_blocks and call in ExecutionEngine.tick

dag_engine.py

@@ -16,6 +16,23 @@ class TrackDAG:
   self.tickets = tickets
   self.ticket_map = {t.id: t for t in tickets}
 
+ def cascade_blocks(self) -> None:
+  """
+        Transitively marks `todo` tickets as `blocked` if any dependency is `blocked`.
+        Runs until stable (handles multi-hop chains: A→B→C where A blocked cascades to B then C).
+        """
+  changed = True
+  while changed:
+   changed = False
+   for ticket in self.tickets:
+    if ticket.status == 'todo':
+     for dep_id in ticket.depends_on:
+      dep = self.ticket_map.get(dep_id)
+      if dep and dep.status == 'blocked':
+       ticket.status = 'blocked'
+       changed = True
+       break
+
  def get_ready_tasks(self) -> List[Ticket]:
   """
         Returns a list of tickets that are in 'todo' status and whose dependencies are all 'completed'.
@@ -116,6 +133,7 @@ class ExecutionEngine:
         Returns:
             A list of ready Ticket objects.
         """
+  self.dag.cascade_blocks()
   ready = self.dag.get_ready_tasks()
   if self.auto_queue:
    for ticket in ready: