Add a `._state._runtime_vars['_registry_addrs']`

Such that it's set to whatever `Actor.reg_addrs: list[tuple]` is during
the actor's init-after-spawn guaranteeing each actor has at least the
registry infos from its parent. Ensure we read this if defined over
`_root._default_lo_addrs` in `._discovery` routines, namely
`.find_actor()` since it's the one API normally used without expecting
the runtime's `current_actor()` to be up.

Update the latest inter-peer cancellation test to use the `reg_addr`
fixture (and thus test this new runtime-vars value via `find_actor()`
usage) since it was failing if run *after* the infected `asyncio` suite
due to registry contact failure.

tests/test_inter_peer_cancellation.py

@@ -939,6 +939,7 @@ async def tell_little_bro(
 def test_peer_spawns_and_cancels_service_subactor(
     debug_mode: bool,
     raise_client_error: str,
+    reg_addr: tuple[str, int],
 ):
     # NOTE: this tests for the modden `mod wks open piker` bug
     # discovered as part of implementing workspace ctx
@@ -956,6 +957,7 @@ def test_peer_spawns_and_cancels_service_subactor(
         async with tractor.open_nursery(
             # NOTE: to halt the peer tasks on ctxc, uncomment this.
             debug_mode=debug_mode,
+            registry_addrs=[reg_addr],
         ) as an:
             server: Portal = await an.start_actor(
                 (server_name := 'spawn_server'),

tractor/_discovery.py

@@ -35,7 +35,10 @@ from ._portal import (
     open_portal,
     LocalPortal,
 )
-from ._state import current_actor, _runtime_vars
+from ._state import (
+    current_actor,
+    _runtime_vars,
+)
 
 
 if TYPE_CHECKING:
@@ -205,7 +208,11 @@ async def find_actor(
         # every call since something may change it globally (eg.
         # like in our discovery test suite)!
         from . import _root
-        registry_addrs = _root._default_lo_addrs
+        registry_addrs = (
+            _runtime_vars['_registry_addrs']
+            or
+            _root._default_lo_addrs
+        )
 
     maybe_portals: list[
         AsyncContextManager[tuple[str, int]]

tractor/_runtime.py

@@ -896,6 +896,7 @@ class Actor:
         self._reg_addrs: list[tuple[str, int]] = []
         if registry_addrs:
             self.reg_addrs: list[tuple[str, int]] = registry_addrs
+            _state._runtime_vars['_registry_addrs'] = registry_addrs
 
     @property
     def reg_addrs(self) -> list[tuple[str, int]]:

tractor/_state.py

@@ -33,7 +33,8 @@ _last_actor_terminated: Actor|None = None
 _runtime_vars: dict[str, Any] = {
     '_debug_mode': False,
     '_is_root': False,
-    '_root_mailbox': (None, None)
+    '_root_mailbox': (None, None),
+    '_registry_addrs': [],
 }