createGraphRunStream

Creates a GraphRunStream with built-in transformers and kicks off the background pump that feeds raw stream chunks through the transformer pipeline.

Built-in transformers are registered in this order:

1. subgraph discovery — materializes SubgraphRunStream handles for each newly observed top-level namespace and announces them on the mux _discoveries log.
2. lifecycle — synthesizes lifecycle channel events.
3. values — powers run.values / run.output.
4. messages — powers run.messages / .messagesFrom.

Subgraph discovery is registered first so that downstream transformers (notably lifecycle) observe child namespaces with their stream handles already in place. User-supplied transformer factories are registered afterwards.