docs(workflow): add comment to NodeState and fix formatting in _workflow_class.py

Change-Id: Ic49dfd0fc7593db81dceac8ea1c5dd69d63d6e74

Author: boyangsvl

src/google/adk/workflow/_node_state.py

@@ -50,7 +50,11 @@ class NodeState(BaseModel):
   """The responses for resuming the node, keyed by interrupt id."""
 
   run_counter: int = Field(default=0, exclude_if=lambda v: v == 0)
-  """Sequential counter incremented each time the node gets a fresh run."""
+  """Sequential counter incremented each time the node gets a fresh run.
+
+  Preserving this count independently of run_id prevents path collisions
+  if a node switches between custom string IDs and auto-generated numeric IDs.
+  """
 
   run_id: str | None = None
   """The run ID of this node run."""

src/google/adk/workflow/_workflow_class.py

@@ -597,7 +597,11 @@ def _restore_static_nodes_from_events(
         # For nodes with events but no output:
         # If wait_for_output is True, they are still WAITING for output.
         # Otherwise, they are considered COMPLETED (e.g., side-effect nodes).
-        status = NodeStatus.WAITING if is_wait_for_output and child.output is None else NodeStatus.COMPLETED
+        status = (
+            NodeStatus.WAITING
+            if is_wait_for_output and child.output is None
+            else NodeStatus.COMPLETED
+        )
         nodes[child_name] = NodeState(
             status=status,
             run_id=existing_evt_run_id,
@@ -701,7 +705,11 @@ def _scan_child_events(self, ctx: Context) -> dict[str, _ChildScanState]:
 
       # New run_id → reset child state (previous run stale).
       # ONLY update run_id from direct child events, not descendants!
-      evt_run_id = event.node_info.path.rsplit('@', 1)[-1] if '@' in event.node_info.path else ''
+      evt_run_id = (
+          event.node_info.path.rsplit('@', 1)[-1]
+          if '@' in event.node_info.path
+          else ''
+      )
       if (
           is_direct_child(event.node_info.path, workflow_path)
           and evt_run_id