Expose it from `._state.current_ipc_ctx()` and set it inside
`._rpc._invoke()` for child and inside `Portal.open_context()` for
parent.
Still need to write a few more tests (particularly demonstrating usage
throughout multiple nested nurseries on each side) but this suffices as
a proto for testing with some debugger request-from-subactor stuff.
Other,
- use new `.devx.pformat.add_div()` for ctxc messages.
- add a block to always traceback dump on corrupted cs stacks.
- better handle non-RAEs exception output-formatting in context
termination summary log message.
- use a summary for `start_status` for msg logging in RPC loop.
51de6bd1bc