refactor: unify system tools as resources

backend/services/workflow_engine.py

@@ -11,7 +11,6 @@ from typing import Any
 
 from services.node_specs import normalize_graph
 from services.runtime_variables import DynamicVariableStore
-from services.system_tools import normalize_system_tools
 
 
 @dataclass(frozen=True)
@@ -25,7 +24,6 @@ class AgentStageConfig:
     vision_enabled: bool
     vision_model_resource_id: str | None
     tool_ids: tuple[str, ...]
-    system_tools: tuple[str, ...]
     state_variable_names: tuple[str, ...]
     knowledge_base_id: str | None
     knowledge_mode: str
@@ -148,9 +146,8 @@ class WorkflowEngine:
                 str(source.get("visionModelResourceId") or "") or None
             ),
             tool_ids=tuple(str(tool_id) for tool_id in source.get("toolIds") or []),
-            # System tools and their writable state scope always belong to the
-            # Agent node. They are permissions, not inheritable model config.
-            system_tools=normalize_system_tools(data.get("systemTools")),
+            # Variable write scope always belongs to the Agent node, even when
+            # its selected tool resources come from Workflow defaults.
             state_variable_names=tuple(
                 dict.fromkeys(
                     str(name)