fix: opt draft storage into real callers

src/wf_api/stores.py

@@ -22,12 +22,21 @@ class WorkflowStores:
     run_store: RunStore
 
 
-def file_workflow_stores(root: str | Path) -> WorkflowStores:
-    """Create process-local file-backed workflow stores under one root."""
+def file_workflow_stores(
+    root: str | Path,
+    *,
+    drafts: bool = False,
+) -> WorkflowStores:
+    """Create file-backed workflow stores, opting into draft persistence.
+
+    Artifact and run stores are needed by every durable workflow server. Draft
+    workspaces are a separate product surface, so avoid constructing their
+    store (which creates its directory) unless a caller explicitly enables it.
+    """
     store_root = Path(root)
     return WorkflowStores(
         artifact_store=FileWorkflowArtifactStore(store_root),
-        draft_workspace_store=FileDraftWorkspaceStore(store_root),
+        draft_workspace_store=(FileDraftWorkspaceStore(store_root) if drafts else None),
         run_store=FileRunStore(store_root),
     )