feat: migrate pipeline input validation to a layer (#1284)

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## Description
<!-- Provide a clear description of the changes in this PR -->

## DCO Affirmation
I affirm that all code in every commit of this pull request conforms to
the terms of the Topoteretes Developer Certificate of Origin.

cognee/modules/pipelines/exceptions/tasks.py

@@ -0,0 +1,18 @@
+from fastapi import status
+from cognee.exceptions import CogneeValidationError
+
+
+class WrongTaskTypeError(CogneeValidationError):
+    """
+    Raised when the tasks argument is not a list of Task class instances.
+    """
+
+    def __init__(
+        self,
+        message: str = "tasks argument must be a list, containing Task class instances.",
+        name: str = "WrongTaskTypeError",
+        status_code=status.HTTP_400_BAD_REQUEST,
+    ):
+        self.message = message
+        self.name = name
+        self.status_code = status_code

cognee/modules/pipelines/layers/__init__.py

@@ -0,0 +1 @@
+from .validate_pipeline_tasks import validate_pipeline_tasks

cognee/modules/pipelines/layers/validate_pipeline_tasks.py

@@ -0,0 +1,20 @@
+from ..tasks.task import Task
+from ..exceptions.tasks import WrongTaskTypeError
+
+
+def validate_pipeline_tasks(tasks: list[Task]):
+    """
+    Validates the tasks argument to ensure it is a list of Task class instances.
+
+    Args:
+        tasks (list[Task]): The list of tasks to be validated.
+    """
+
+    if not isinstance(tasks, list):
+        raise WrongTaskTypeError(f"tasks argument must be a list, got {type(tasks).__name__}.")
+
+    for task in tasks:
+        if not isinstance(task, Task):
+            raise WrongTaskTypeError(
+                f"tasks argument must be a list of Task class instances, got {type(task).__name__} in the list."
+            )

cognee/modules/pipelines/operations/pipeline.py

@@ -10,7 +10,7 @@ from cognee.modules.data.methods.get_dataset_data import get_dataset_data
 from cognee.modules.data.models import Data, Dataset
 from cognee.modules.pipelines.operations.run_tasks import run_tasks
 from cognee.modules.pipelines.utils import generate_pipeline_id
-
+from cognee.modules.pipelines.layers import validate_pipeline_tasks
 from cognee.modules.pipelines.tasks.task import Task
 from cognee.modules.users.models import User
 from cognee.modules.pipelines.operations import log_pipeline_run_initiated
@@ -61,6 +61,8 @@ async def run_pipeline(
     context: dict = None,
     incremental_loading=False,
 ):
+    validate_pipeline_tasks(tasks)
+
     # Will only be used if ENABLE_BACKEND_ACCESS_CONTROL is set to True
     await set_database_global_context_variables(dataset.id, dataset.owner_id)
 
@@ -94,13 +96,6 @@ async def run_pipeline(
         yield process_pipeline_status
         return
 
-    if not isinstance(tasks, list):
-        raise ValueError("Tasks must be a list")
-
-    for task in tasks:
-        if not isinstance(task, Task):
-            raise ValueError(f"Task {task} is not an instance of Task")
-
     pipeline_run = run_tasks(
         tasks, dataset.id, data, user, pipeline_name, context, incremental_loading
     )