Show runtime nursery frames on internal errors

Much like other recent changes attempt to detect runtime-bug-causing
crashes and only show the runtime-endpoint frame when present.

Adds a `ActorNursery._scope_error: BaseException|None` attr to aid with
detection. Also toss in some todo notes for removing and replacing the
`.run_in_actor()` method API.

tractor/_supervise.py

@@ -84,6 +84,7 @@ class ActorNursery:
         ria_nursery: trio.Nursery,
         da_nursery: trio.Nursery,
         errors: dict[tuple[str, str], BaseException],
+
     ) -> None:
         # self.supervisor = supervisor  # TODO
         self._actor: Actor = actor
@@ -105,6 +106,7 @@ class ActorNursery:
         self._at_least_one_child_in_debug: bool = False
         self.errors = errors
         self.exited = trio.Event()
+        self._scope_error: BaseException|None = None
 
         # NOTE: when no explicit call is made to
         # `.open_root_actor()` by application code,
@@ -117,7 +119,9 @@ class ActorNursery:
     async def start_actor(
         self,
         name: str,
+
         *,
+
         bind_addrs: list[tuple[str, int]] = [_default_bind_addr],
         rpc_module_paths: list[str]|None = None,
         enable_modules: list[str]|None = None,
@@ -125,6 +129,7 @@ class ActorNursery:
         nursery: trio.Nursery|None = None,
         debug_mode: bool|None = None,
         infect_asyncio: bool = False,
+
     ) -> Portal:
         '''
         Start a (daemon) actor: an process that has no designated
@@ -189,6 +194,13 @@ class ActorNursery:
             )
         )
 
+    # TODO: DEPRECATE THIS:
+    # -[ ] impl instead as a hilevel wrapper on
+    #   top of a `@context` style invocation.
+    #  |_ dynamic @context decoration on child side
+    #  |_ implicit `Portal.open_context() as (ctx, first):`
+    #    and `return first` on parent side.
+    # -[ ] use @api_frame on the wrapper
     async def run_in_actor(
         self,
 
@@ -221,7 +233,7 @@ class ActorNursery:
             # use the explicit function name if not provided
             name = fn.__name__
 
-        portal = await self.start_actor(
+        portal: Portal = await self.start_actor(
             name,
             enable_modules=[mod_path] + (
                 enable_modules or rpc_module_paths or []
@@ -250,6 +262,7 @@ class ActorNursery:
         )
         return portal
 
+    # @api_frame
     async def cancel(
         self,
         hard_kill: bool = False,
@@ -346,7 +359,12 @@ async def _open_and_supervise_one_cancels_all_nursery(
     actor: Actor,
 
 ) -> typing.AsyncGenerator[ActorNursery, None]:
-    __tracebackhide__ = True
+
+    # normally don't need to show user by default
+    __tracebackhide__: bool = True
+
+    outer_err: BaseException|None = None
+    inner_err: BaseException|None = None
 
     # the collection of errors retreived from spawned sub-actors
     errors: dict[tuple[str, str], BaseException] = {}
@@ -356,7 +374,7 @@ async def _open_and_supervise_one_cancels_all_nursery(
     # handling errors that are generated by the inner nursery in
     # a supervisor strategy **before** blocking indefinitely to wait for
     # actors spawned in "daemon mode" (aka started using
-    # ``ActorNursery.start_actor()``).
+    # `ActorNursery.start_actor()`).
 
     # errors from this daemon actor nursery bubble up to caller
     async with trio.open_nursery() as da_nursery:
@@ -391,7 +409,8 @@ async def _open_and_supervise_one_cancels_all_nursery(
                     )
                     an._join_procs.set()
 
-                except BaseException as inner_err:
+                except BaseException as _inner_err:
+                    inner_err = _inner_err
                     errors[actor.uid] = inner_err
 
                     # If we error in the root but the debugger is
@@ -469,8 +488,10 @@ async def _open_and_supervise_one_cancels_all_nursery(
             Exception,
             BaseExceptionGroup,
             trio.Cancelled
+        ) as _outer_err:
+            outer_err = _outer_err
 
-        ) as err:
+            an._scope_error = outer_err or inner_err
 
             # XXX: yet another guard before allowing the cancel
             # sequence in case a (single) child is in debug.
@@ -485,7 +506,7 @@ async def _open_and_supervise_one_cancels_all_nursery(
             if an._children:
                 log.cancel(
                     'Actor-nursery cancelling due error type:\n'
-                    f'{err}\n'
+                    f'{outer_err}\n'
                 )
                 with trio.CancelScope(shield=True):
                     await an.cancel()
@@ -512,6 +533,13 @@ async def _open_and_supervise_one_cancels_all_nursery(
                 else:
                     raise list(errors.values())[0]
 
+            # show frame on any (likely) internal error
+            if (
+                not an.cancelled
+                and an._scope_error
+            ):
+                __tracebackhide__: bool = False
+
         # da_nursery scope end - nursery checkpoint
     # final exit
 
@@ -537,7 +565,7 @@ async def open_nursery(
     which cancellation scopes correspond to each spawned subactor set.
 
     '''
-    __tracebackhide__ = True
+    __tracebackhide__: bool = True
     implicit_runtime: bool = False
     actor: Actor = current_actor(err_on_no_runtime=False)
     an: ActorNursery|None = None
@@ -588,6 +616,14 @@ async def open_nursery(
                 an.exited.set()
 
     finally:
+        # show frame on any internal runtime-scope error
+        if (
+            an
+            and not an.cancelled
+            and an._scope_error
+        ):
+            __tracebackhide__: bool = False
+
         msg: str = (
             'Actor-nursery exited\n'
             f'|_{an}\n'