diff --git a/tractor/_root.py b/tractor/_root.py
index 1bcfa00b..81ff884b 100644
--- a/tractor/_root.py
+++ b/tractor/_root.py
@@ -217,11 +217,16 @@ async def open_root_actor(
     ):
         if enable_transports is None:
             enable_transports: list[str] = _state.current_ipc_protos()
+        else:
+            _state._runtime_vars['_enable_tpts'] = enable_transports
 
-            # TODO! support multi-tpts per actor! Bo
-            assert (
-                len(enable_transports) == 1
-            ), 'No multi-tpt support yet!'
+        # TODO! support multi-tpts per actor!
+        # Bo
+        if not len(enable_transports) == 1:
+            raise RuntimeError(
+                f'No multi-tpt support yet!\n'
+                f'enable_transports={enable_transports!r}\n'
+            )
 
         _debug.hide_runtime_frames()
         __tracebackhide__: bool = hide_tb
diff --git a/tractor/_runtime.py b/tractor/_runtime.py
index b25f6bc1..015c235c 100644
--- a/tractor/_runtime.py
+++ b/tractor/_runtime.py
@@ -877,9 +877,7 @@ class Actor:
             return (
                 chan,
                 accept_addrs,
-                None,
-                # ^TODO, preferred tpts list from rent!
-                # -[ ] need to extend the `SpawnSpec` tho!
+                _state._runtime_vars['_enable_tpts']
             )
 
         # failed to connect back?
@@ -1453,10 +1451,12 @@ async def async_main(
                 # all sub-actors should be able to speak to
                 # their root actor over that channel.
                 if _state._runtime_vars['_is_root']:
+                    raddrs: list[Address] = _state._runtime_vars['_root_addrs']
                     for addr in accept_addrs:
-                        waddr = wrap_address(addr)
-                        if waddr == waddr.get_root():
-                            _state._runtime_vars['_root_mailbox'] = addr
+                        waddr: Address = wrap_address(addr)
+                        raddrs.append(addr)
+                    else:
+                        _state._runtime_vars['_root_mailbox'] = raddrs[0]
 
                 # Register with the arbiter if we're told its addr
                 log.runtime(
diff --git a/tractor/_state.py b/tractor/_state.py
index bc12d0de..4eba74f0 100644
--- a/tractor/_state.py
+++ b/tractor/_state.py
@@ -37,14 +37,28 @@ if TYPE_CHECKING:
     from ._context import Context
 
 
+# default IPC transport protocol settings
+TransportProtocolKey = Literal[
+    'tcp',
+    'uds',
+]
+_def_tpt_proto: TransportProtocolKey = 'tcp'
+
 _current_actor: Actor|None = None  # type: ignore # noqa
 _last_actor_terminated: Actor|None = None
 
 # TODO: mk this a `msgspec.Struct`!
 _runtime_vars: dict[str, Any] = {
     '_debug_mode': False,
-    '_is_root': False,
-    '_root_mailbox': (None, None),
+    # root of actor-process tree info
+    '_is_root': False,  # bool
+    '_root_mailbox': (None, None),  # tuple[str|None, str|None]
+    '_root_addrs': [],  # tuple[str|None, str|None]
+
+    # parent->chld ipc protocol caps
+    '_enable_tpts': [_def_tpt_proto],
+
+    # registrar info
     '_registry_addrs': [],
 
     '_is_infected_aio': False,
@@ -172,14 +186,6 @@ def get_rt_dir(
     return rtdir
 
 
-# default IPC transport protocol settings
-TransportProtocolKey = Literal[
-    'tcp',
-    'uds',
-]
-_def_tpt_proto: TransportProtocolKey = 'tcp'
-
-
 def current_ipc_protos() -> list[str]:
     '''
     Return the list of IPC transport protocol keys currently
@@ -189,4 +195,4 @@ def current_ipc_protos() -> list[str]:
     concrete-backend sub-types defined throughout `tractor.ipc`.
 
     '''
-    return [_def_tpt_proto]
+    return _runtime_vars['_enable_tpts']
diff --git a/tractor/msg/types.py b/tractor/msg/types.py
index 86752aba..aaf8d137 100644
--- a/tractor/msg/types.py
+++ b/tractor/msg/types.py
@@ -170,6 +170,7 @@ class SpawnSpec(
     # a hard `Struct` def for all of these fields!
     _parent_main_data: dict
     _runtime_vars: dict[str, Any]
+    # ^NOTE see `._state._runtime_vars: dict`
 
     # module import capability
     enable_modules: dict[str, str]