Expose per-actor registry addrs via `.reg_addrs`

Since it's handy to be able to debug the *writing* of this instance var
(particularly when checking state passed down to a child in
`Actor._from_parent()`), rename and wrap the underlying
`Actor._reg_addrs` as a settable `@property` and add validation to
the `.setter` for sanity - actor discovery is a critical functionality.

Other tweaks:
- fix `.cancel_soon()` to pass expected argument..
- update internal runtime error message to be simpler and link to GH issues.
- use new `Actor.reg_addrs` throughout core.

tractor/_runtime.py

@@ -553,12 +553,6 @@ class Actor:
             )
             registry_addrs: list[tuple[str, int]] = [arbiter_addr]
 
-        self._reg_addrs: list[tuple[str, int]] = (
-            registry_addrs
-            or
-            None
-        )
-
         # marked by the process spawning backend at startup
         # will be None for the parent most process started manually
         # by the user (currently called the "arbiter")
@@ -591,6 +585,44 @@ class Actor:
             ActorNursery | None,
         ] = {}  # type: ignore  # noqa
 
+        # when provided, init the registry addresses property from
+        # input via the validator.
+        self._reg_addrs: list[tuple[str, int]] = []
+        if registry_addrs:
+            self.reg_addrs: list[tuple[str, int]] = registry_addrs
+
+    @property
+    def reg_addrs(self) -> list[tuple[str, int]]:
+        '''
+        List of (socket) addresses for all known (and contactable)
+        registry actors.
+
+        '''
+        return self._reg_addrs
+
+    @reg_addrs.setter
+    def reg_addrs(
+        self,
+        addrs: list[tuple[str, int]],
+    ) -> None:
+        if not addrs:
+            log.warning(
+                'Empty registry address list is invalid:\n'
+                f'{addrs}'
+            )
+            return
+
+        # always sanity check the input list since it's critical
+        # that addrs are correct for discovery sys operation.
+        for addr in addrs:
+            if not isinstance(addr, tuple):
+                raise ValueError(
+                    'Expected `Actor.reg_addrs: list[tuple[str, int]]`\n'
+                    f'Got {addrs}'
+                )
+
+            self._reg_addrs = addrs
+
     async def wait_for_peer(
         self, uid: tuple[str, str]
     ) -> tuple[trio.Event, Channel]:
@@ -670,9 +702,10 @@ class Actor:
         stream: trio.SocketStream,
 
     ) -> None:
-        """Entry point for new inbound connections to the channel server.
+        '''
+        Entry point for new inbound connections to the channel server.
 
-        """
+        '''
         self._no_more_peers = trio.Event()  # unset
 
         chan = Channel.from_stream(stream)
@@ -792,17 +825,21 @@ class Actor:
 
                 if disconnected:
                     # if the transport died and this actor is still
-                    # registered within a local nursery, we report that the
+                    # registered within a local nursery, we report
-                    # IPC layer may have failed unexpectedly since it may be
+                    # that the IPC layer may have failed
-                    # the cause of other downstream errors.
+                    # unexpectedly since it may be the cause of
+                    # other downstream errors.
                     entry = local_nursery._children.get(uid)
                     if entry:
                         _, proc, _ = entry
 
-                        poll = getattr(proc, 'poll', None)
+                        if (
-                        if poll and poll() is None:
+                            (poll := getattr(proc, 'poll', None))
+                            and poll() is None
+                        ):
                             log.cancel(
-                                f'Actor {uid} IPC broke but proc is alive?'
+                                f'Actor {uid} IPC broke but proc is alive?\n'
+                                'Attempting to self cancel..'
                             )
 
             # ``Channel`` teardown and closure sequence
@@ -1016,14 +1053,18 @@ class Actor:
                 _state._runtime_vars.update(rvs)
 
                 for attr, value in parent_data.items():
-
+                    if (
-                    if attr == '_reg_addrs':
+                        attr == 'reg_addrs'
+                        and value
+                    ):
                         # XXX: ``msgspec`` doesn't support serializing tuples
                         # so just cash manually here since it's what our
                         # internals expect.
-                        self._reg_addrs = [
+                        # TODO: we don't really NEED these as
-                            tuple(val) for val in value
+                        # tuples so we can probably drop this
-                        ] if value else None
+                        # casting since apparently in python lists
+                        # are "more efficient"?
+                        self.reg_addrs = [tuple(val) for val in value]
 
                     else:
                         setattr(self, attr, value)
@@ -1099,7 +1140,10 @@ class Actor:
 
         '''
         assert self._service_n
-        self._service_n.start_soon(self.cancel)
+        self._service_n.start_soon(
+            self.cancel,
+            self.uid,
+        )
 
     async def cancel(
         self,
@@ -1445,9 +1489,12 @@ async def async_main(
                 # if addresses point to the same actor..
                 # So we need a way to detect that? maybe iterate
                 # only on unique actor uids?
-                for addr in actor._reg_addrs:
+                for addr in actor.reg_addrs:
+                    try:
                         assert isinstance(addr, tuple)
                         assert addr[1]  # non-zero after bind
+                    except AssertionError:
+                        await _debug.pause()
 
                     async with get_registry(*addr) as reg_portal:
                         for accept_addr in accept_addrs:
@@ -1500,12 +1547,14 @@ async def async_main(
             # once we have that all working with std streams locking?
             log.exception(
                 f"Actor errored and failed to register with arbiter "
-                f"@ {actor._reg_addrs[0]}?")
+                f"@ {actor.reg_addrs[0]}?")
             log.error(
-                "\n\n\t^^^ THIS IS PROBABLY A TRACTOR BUGGGGG!!! ^^^\n"
+                "\n\n\t^^^ THIS IS PROBABLY AN INTERNAL `tractor` BUG! ^^^\n\n"
-                "\tCALMLY CALL THE AUTHORITIES AND HIDE YOUR CHILDREN.\n\n"
+                "\t>> CALMLY CALL THE AUTHORITIES AND HIDE YOUR CHILDREN <<\n\n"
-                "\tIf this is a sub-actor likely its parent will keep running "
+                "\tIf this is a sub-actor hopefully its parent will keep running "
-                "\tcorrectly if this error is caught and ignored.."
+                "correctly presuming this error was safely ignored..\n\n"
+                "\tPLEASE REPORT THIS TRACEBACK IN A BUG REPORT: "
+                "https://github.com/goodboy/tractor/issues\n"
             )
 
         if actor._parent_chan:
@@ -1546,7 +1595,7 @@ async def async_main(
             and not actor.is_registrar
         ):
             failed: bool = False
-            for addr in actor._reg_addrs:
+            for addr in actor.reg_addrs:
                 assert isinstance(addr, tuple)
                 with trio.move_on_after(0.5) as cs:
                     cs.shield = True