fix(aci): prevent deletion of system-created monitors in API

src/sentry/workflow_engine/endpoints/organization_detector_details.py

@@ -21,7 +21,6 @@
 )
 from sentry.apidocs.parameters import DetectorParams, GlobalParams
 from sentry.db.postgres.transactions import in_test_hide_transaction_boundary
-from sentry.grouping.grouptype import ErrorGroupType
 from sentry.incidents.grouptype import MetricIssue
 from sentry.incidents.metric_issue_detector import schedule_update_project_config
 from sentry.issues import grouptype
@@ -31,6 +30,7 @@
 from sentry.workflow_engine.endpoints.serializers.detector_serializer import DetectorSerializer
 from sentry.workflow_engine.endpoints.validators.detector_workflow import (
     BulkDetectorWorkflowsValidator,
+    can_delete_detector,
     can_edit_detector,
 )
 from sentry.workflow_engine.endpoints.validators.utils import get_unknown_detector_type_error
@@ -193,12 +193,9 @@ def delete(self, request: Request, organization: Organization, detector: Detecto
         """
         Delete a detector
         """
-        if not can_edit_detector(detector, request):
+        if not can_delete_detector(detector, request):
             raise PermissionDenied
 
-        if detector.type == ErrorGroupType.slug:
-            return Response(status=403)
-
         validator = get_detector_validator(
             request, detector.project, detector.type, instance=detector
         )

src/sentry/workflow_engine/endpoints/organization_detector_index.py

@@ -50,6 +50,7 @@
 from sentry.workflow_engine.endpoints.validators.base import BaseDetectorTypeValidator
 from sentry.workflow_engine.endpoints.validators.detector_workflow import (
     BulkDetectorWorkflowsValidator,
+    can_delete_detectors,
     can_edit_detectors,
 )
 from sentry.workflow_engine.endpoints.validators.detector_workflow_mutation import (
@@ -506,7 +507,7 @@ def delete(self, request: Request, organization: Organization) -> Response:
             )
 
         # Check if the user has edit permissions for all detectors
-        if not can_edit_detectors(queryset, request):
+        if not can_delete_detectors(queryset, request):
             raise PermissionDenied
 
         for detector in queryset:

src/sentry/workflow_engine/endpoints/validators/detector_workflow.py

@@ -69,6 +69,31 @@ def can_edit_detector(detector: Detector, request: Request) -> bool:
     return can_edit_user_created_detectors(request, detector.project)
 
 
+def can_delete_detectors(detectors: QuerySet[Detector], request: Request) -> bool:
+    """
+    Determine if the requesting user has access to delete the given detectors.
+    Only user-created detectors can be deleted, and require "alerts:write" permission.
+    """
+    if any(is_system_created_detector(detector) for detector in detectors):
+        return False
+
+    projects = Project.objects.filter(
+        id__in=detectors.values_list("project_id", flat=True).distinct()
+    )
+    return all(can_edit_user_created_detectors(request, project) for project in projects)
+
+
+def can_delete_detector(detector: Detector, request: Request) -> bool:
+    """
+    Determine if the requesting user has access to delete the given detector.
+    Only user-created detectors can be deleted, and require "alerts:write" permission.
+    """
+    if is_system_created_detector(detector):
+        return False
+
+    return can_edit_user_created_detectors(request, detector.project)
+
+
 def can_edit_detector_workflow_connections(detector: Detector, request: Request) -> bool:
     """
     Anyone with alert write access to the project can connect/disconnect detectors of any type,

tests/sentry/workflow_engine/endpoints/test_organization_detector_details.py

@@ -843,3 +843,19 @@ def test_anomaly_detection(
         mock_seer_request.assert_called_once_with(
             source_id=int(self.data_source.source_id), organization=self.organization
         )
+
+    def test_cannot_delete_system_created_detector(self) -> None:
+        error_detector = self.create_detector(
+            project=self.project,
+            name="Error Detector",
+            type=ErrorGroupType.slug,
+        )
+
+        self.get_error_response(self.organization.slug, error_detector.id, status_code=403)
+
+        # Verify detector was not deleted
+        error_detector.refresh_from_db()
+        assert error_detector.status != ObjectStatus.PENDING_DELETION
+        assert not RegionScheduledDeletion.objects.filter(
+            model_name="Detector", object_id=error_detector.id
+        ).exists()

tests/sentry/workflow_engine/endpoints/test_organization_detector_index.py

@@ -1795,3 +1795,54 @@ def test_delete_detectors_permission_denied(self) -> None:
 
         # Verify detector was not affected
         self.assert_unaffected_detectors([self.detector, other_detector])
+
+    def test_delete_system_created_detector_by_id_prevented(self) -> None:
+        # Test that system-created detectors cannot be deleted via bulk delete by ID
+        error_detector = self.create_detector(
+            project=self.project,
+            name="Error Detector",
+            type=ErrorGroupType.slug,
+        )
+
+        self.get_error_response(
+            self.organization.slug,
+            qs_params={"id": str(error_detector.id)},
+            status_code=403,
+        )
+
+        self.assert_unaffected_detectors([error_detector])
+
+    def test_delete_system_and_user_created(self) -> None:
+        # Test that permission is denied when request includes system-created detectors
+        error_detector = self.create_detector(
+            project=self.project,
+            name="Error Detector",
+            type=ErrorGroupType.slug,
+        )
+
+        self.get_error_response(
+            self.organization.slug,
+            qs_params=[
+                ("id", str(self.detector.id)),
+                ("id", str(error_detector.id)),
+            ],
+            status_code=403,
+        )
+
+        self.assert_unaffected_detectors([self.detector, error_detector])
+
+    def test_delete_system_and_user_created_with_query_filters(self) -> None:
+        # Test that permission is denied when query filter request includes system-created detectors
+        error_detector = self.create_detector(
+            project=self.project,
+            name="Test Error Detector",
+            type=ErrorGroupType.slug,
+        )
+
+        self.get_error_response(
+            self.organization.slug,
+            qs_params={"query": "Test", "project": self.project.id},
+            status_code=403,
+        )
+
+        self.assert_unaffected_detectors([self.detector, error_detector])