add the async twin of Ts

docs/wf_core_architecture.md

@@ -136,9 +136,11 @@ limits and intended adapter seam.
   includes node, condition, foreach, join, and interrupt steps; `Workflow` does
   not contain nested workflow/subgraph steps.
 - Nested subgraph interruption is not first-class yet. The current
-  `wf_authoring` subgraph helper wraps a child workflow as an ordinary node and
-  validates the child output; it does not preserve a child run state that can
-  interrupt, bubble to the parent, and later resume inside the child.
+  `wf_authoring` subgraph helpers wrap a child workflow as an ordinary sync or
+  async node and validate the child output; they do not preserve a child run
+  state that can interrupt, bubble to the parent, and later resume inside the
+  child. See `examples/authoring_workflow_as_node.py` for the current
+  wrapper-node shape.
 - Saved workflow-as-node execution with interrupts requires a core runtime
   upgrade: nested run state, child-frame trace preservation, interrupt bubbling
   with path metadata, and resume back into the child workflow.

docs/workflow_artifacts.md

@@ -637,11 +637,17 @@ diagnostics before attempting persistent nested resume.
 
 Native subgraphs are not in `wf_core` yet. The current core `Step` model has
 node, condition, foreach, join, and interrupt steps, but no subgraph step. The
-current `wf_authoring.subgraph_node` helper executes a child workflow as a plain
-node and validates the child output. Future saved-workflow-as-node execution
+current `wf_authoring.subgraph_node` and `async_subgraph_node` helpers execute
+a child workflow as a plain node and validate the child output. The async helper
+is explicit because hiding `asyncio.run()` inside the sync wrapper would break
+inside already-running event loops. Future saved-workflow-as-node execution
 needs a real child run state if child interrupts should pause the parent and
 later resume the child.
 
+See `examples/authoring_workflow_as_node.py` for the current wrapper-node
+approach. In that example the parent trace sees one node call; the child
+workflow's internal trace is not embedded in the parent run state.
+
 Until that core upgrade exists, artifact tooling must not assume that an
 interrupting saved workflow can safely be used as a child node. Top-level saved
 workflows with interrupt nodes are valid, but nested interrupting workflows