refactor: remove legacy assistant compatibility

backend/services/system_tools.py

@@ -38,7 +38,7 @@ RESERVED_TOOL_NAMES = frozenset(
 
 
 def system_tool_kind(definition: Mapping[str, Any] | None) -> str | None:
-    """Compatibility helper for old fixtures and the one-time migration."""
+    """Read the platform tool kind from its runtime definition."""
 
     config = (definition or {}).get("config")
     if not isinstance(config, Mapping):
@@ -85,7 +85,12 @@ def runtime_system_tools(
                 ),
                 definition={
                     "type": "system",
-                    "config": {"kind": kind, **normalized_config},
+                    "config": {
+                        "kind": kind,
+                        "allow_interruptions": True,
+                        "execution_mode": "immediate",
+                        **normalized_config,
+                    },
                 },
             )
         )