diff --git a/strix/runtime/session_manager.py b/strix/runtime/session_manager.py
index 2f83fd1d..9523d0f4 100644
--- a/strix/runtime/session_manager.py
+++ b/strix/runtime/session_manager.py
@@ -158,7 +158,7 @@ def build_manifest_grants(local_sources: list[dict[str, Any]]) -> list[SandboxPa
         if not ws_subdir or not host_path:
             continue
         resolved = Path(host_path).expanduser().resolve()
-        grants.append(SandboxPathGrant(path=resolved, read_only=True))
+        grants.append(SandboxPathGrant(path=str(resolved), read_only=True))
     return grants