foreach container arg to get the path treatment too!

src/wf_core/models/steps.py

@@ -124,7 +124,7 @@ class ForeachNode(BaseModel):
 
     id: str
     type: Literal["foreach"]
-    over: str
+    over: GraphSourcePath
     as_: str = Field(alias="as")
     mode: Literal["serial", "parallel"] = "serial"
     on_item_error: Literal["fail", "collect", "skip"] = "fail"

src/wf_core/runtime/ops/foreach.py

@@ -26,14 +26,14 @@ def step_foreach(
     progress = progress_map.setdefault(step.id, {"index": 0})
 
     iterable = safe_resolve_path(
-        step.over,
+        str(step.over),
         state=run.state,
         workflow_input=run.workflow_input,
         context=frame_context_values(frame),
     )
     if not isinstance(iterable, list):
         raise WorkflowExecutionError(
-            f"foreach source {step.over!r} must resolve to a list"
+            f"foreach source {str(step.over)!r} must resolve to a list"
         )
 
     loop_index = progress["index"]