diff --git a/strix/runtime/docker_client.py b/strix/runtime/docker_client.py
index 49cb3e7d..497ae2f2 100644
--- a/strix/runtime/docker_client.py
+++ b/strix/runtime/docker_client.py
@@ -48,7 +48,7 @@ logger = logging.getLogger(__name__)
 class StrixDockerSandboxClient(DockerSandboxClient):
     # Host directories to bind-mount into the container, set by the docker
     # backend before ``create()``. Each item is ``{source, target, read_only}``.
-    strix_bind_mounts: list[dict[str, Any]]
+    strix_bind_mounts: list[dict[str, Any]] = []  # overridden per-instance in backends.py
 
     async def _create_container(
         self,