1 files changed, 4 insertions, 4 deletions
diff --git a/src/Agent.Core/Tools/TaskGraphToolHandler.cs b/src/Agent.Core/Tools/TaskGraphToolHandler.cs
index edc1cc5..10094d3 100644
--- a/src/Agent.Core/Tools/TaskGraphToolHandler.cs
+++ b/src/Agent.Core/Tools/TaskGraphToolHandler.cs
@@ -21,13 +21,13 @@ public sealed class TaskGraphToolHandler(int maxTasks = 32, SessionStore? sessio
         TaskGraph graph = new(maxTasks);
         if (sessions is not null && sessions.TryGet(sessionId, out AgentSession? session) && session is not null)
         {
-            if (!session.TaskGraphs.TryAdd(taskId, graph))
-                throw new InvalidOperationException($"TaskGraph for '{taskId}' already exists in session '{sessionId}'.");
+            // PlanAsync may have already created a TaskGraph for this taskId.
+            // If so, keep the planned graph; otherwise add a new empty one.
+            session.TaskGraphs.TryAdd(taskId, graph);
         }
         else
         {
-            if (!_fallbackGraphs.TryAdd(taskId, graph))
-                throw new InvalidOperationException($"TaskGraph for '{taskId}' already exists.");
+            _fallbackGraphs.TryAdd(taskId, graph);
         }
     }