fixing ignored history lenght in task/get

Author: maeste

src/a2a/server/request_handlers/default_request_handler.py

@@ -112,6 +112,26 @@ async def on_get_task(
         task: Task | None = await self.task_store.get(params.id)
         if not task:
             raise ServerError(error=TaskNotFoundError())
+
+        # Apply historyLength parameter if specified
+        if params.history_length is not None and task.history:
+            # Limit history to the most recent N messages
+            limited_history = (
+                task.history[-params.history_length :]
+                if params.history_length > 0
+                else []
+            )
+            # Create a new task instance with limited history
+            task = Task(
+                id=task.id,
+                context_id=task.context_id,
+                status=task.status,
+                artifacts=task.artifacts,
+                history=limited_history,
+                metadata=task.metadata,
+                kind=task.kind,
+            )
+
         return task
 
     async def on_cancel_task(