Adjust `test_trio_prestarted_task_bubbles()` suite to expect non-eg raises

Was failing due to the `.fail_after()` timeout being *too short* and
somehow the new interplay of that with strict-exception groups resulting
in the `TooSlowError` never raising but instead an eg with the embedded
`AssertionError`?? I still don't really get it honestly..

I've written up lengthy notes around the different `delay` settings that
can be used to see the diff outcomes, the failing case being the one
i still don't really grok and think is justification for `trio` to
bubble inner `Cancelled`s differently possibly?

For now i've included the original failing case as an `xfail`
parametrization for now which will hopefully drive a follow lowlevel
`trio` test in `test_trioisms`!

examples/trio/send_chan_aclose_masks_beg.py

@@ -0,0 +1,145 @@
+from contextlib import (
+    contextmanager as cm,
+    # TODO, any diff in async case(s)??
+    # asynccontextmanager as acm,
+)
+from functools import partial
+
+import tractor
+import trio
+
+
+log = tractor.log.get_logger(__name__)
+tractor.log.get_console_log('info')
+
+@cm
+def teardown_on_exc(
+    raise_from_handler: bool = False,
+):
+    '''
+    You could also have a teardown handler which catches any exc and
+    does some required teardown. In this case the problem is
+    compounded UNLESS you ensure the handler's scope is OUTSIDE the
+    `ux.aclose()`.. that is in the caller's enclosing scope.
+
+    '''
+    try:
+        yield
+    except BaseException as _berr:
+        berr = _berr
+        log.exception(
+            f'Handling termination teardown in child due to,\n'
+            f'{berr!r}\n'
+        )
+        if raise_from_handler:
+            # XXX teardown ops XXX
+            # on termination these steps say need to be run to
+            # ensure wider system consistency (like the state of
+            # remote connections/services).
+            #
+            # HOWEVER, any bug in this teardown code is also
+            # masked by the `tx.aclose()`!
+            # this is also true if `_tn.cancel_scope` is
+            # `.cancel_called` by the parent in a graceful
+            # request case..
+
+            # simulate a bug in teardown handler.
+            raise RuntimeError(
+                'woopsie teardown bug!'
+            )
+
+        raise  # no teardown bug.
+
+
+async def finite_stream_to_rent(
+    tx: trio.abc.SendChannel,
+    child_errors_mid_stream: bool,
+
+    task_status: trio.TaskStatus[
+        trio.CancelScope,
+    ] = trio.TASK_STATUS_IGNORED,
+):
+    async with (
+        # XXX without this unmasker the mid-streaming RTE is never
+        # reported since it is masked by the `tx.aclose()`
+        # call which in turn raises `Cancelled`!
+        #
+        # NOTE, this is WITHOUT doing any exception handling
+        # inside the child  task!
+        #
+        # TODO, uncomment next LoC to see the supprsessed beg[RTE]!
+        # tractor.trionics.maybe_raise_from_masking_exc(),
+
+        tx as tx,  # .aclose() is the guilty masker chkpt!
+        trio.open_nursery() as _tn,
+    ):
+        # pass our scope back to parent for supervision\
+        # control.
+        task_status.started(_tn.cancel_scope)
+
+        with teardown_on_exc(
+            raise_from_handler=not child_errors_mid_stream,
+        ):
+            for i in range(100):
+                log.info(
+                    f'Child tx {i!r}\n'
+                )
+                if (
+                    child_errors_mid_stream
+                    and
+                    i == 66
+                ):
+                    # oh wait but WOOPS there's a bug
+                    # in that teardown code!?
+                    raise RuntimeError(
+                        'woopsie, a mid-streaming bug!?'
+                    )
+
+                await tx.send(i)
+
+
+async def main(
+    # TODO! toggle this for the 2 cases!
+    # 1. child errors mid-stream while parent is also requesting
+    #   (graceful) cancel of that child streamer.
+    #
+    # 2. child contains a teardown handler which contains a
+    #   bug and raises.
+    #
+    child_errors_mid_stream: bool,
+):
+    tx, rx = trio.open_memory_channel(1)
+
+    async with (
+        trio.open_nursery() as tn,
+        rx as rx,
+    ):
+
+        _child_cs = await tn.start(
+            partial(
+                finite_stream_to_rent,
+                child_errors_mid_stream=child_errors_mid_stream,
+                tx=tx,
+            )
+        )
+        async for msg in rx:
+            log.info(
+                f'Rent rx {msg!r}\n'
+            )
+
+            # simulate some external cancellation
+            # request **JUST BEFORE** the child errors.
+            if msg == 65:
+                log.cancel(
+                    f'Cancelling parent on,\n'
+                    f'msg={msg}\n'
+                    f'\n'
+                    f'Simulates OOB cancel request!\n'
+                )
+                tn.cancel_scope.cancel()
+
+
+if __name__ == '__main__':
+
+    for case in [True, False]:
+        trio.run(main, case)

tests/devx/test_debugger.py

@@ -317,7 +317,6 @@ def test_subactor_breakpoint(
 
     assert in_prompt_msg(
         child, [
-        'MessagingError:',
         'RemoteActorError:',
          "('breakpoint_forever'",
          'bdb.BdbQuit',

tests/test_cancellation.py

@@ -284,20 +284,32 @@ async def test_cancel_infinite_streamer(start_method):
     ],
 )
 @tractor_test
-async def test_some_cancels_all(num_actors_and_errs, start_method, loglevel):
+async def test_some_cancels_all(
-    """Verify a subset of failed subactors causes all others in
+    num_actors_and_errs: tuple,
+    start_method: str,
+    loglevel: str,
+):
+    '''
+    Verify a subset of failed subactors causes all others in
     the nursery to be cancelled just like the strategy in trio.
 
     This is the first and only supervisory strategy at the moment.
-    """
+
-    num_actors, first_err, err_type, ria_func, da_func = num_actors_and_errs
+    '''
+    (
+        num_actors,
+        first_err,
+        err_type,
+        ria_func,
+        da_func,
+    ) = num_actors_and_errs
     try:
-        async with tractor.open_nursery() as n:
+        async with tractor.open_nursery() as an:
 
             # spawn the same number of deamon actors which should be cancelled
             dactor_portals = []
             for i in range(num_actors):
-                dactor_portals.append(await n.start_actor(
+                dactor_portals.append(await an.start_actor(
                     f'deamon_{i}',
                     enable_modules=[__name__],
                 ))
@@ -307,7 +319,7 @@ async def test_some_cancels_all(num_actors_and_errs, start_method, loglevel):
             for i in range(num_actors):
                 # start actor(s) that will fail immediately
                 riactor_portals.append(
-                    await n.run_in_actor(
+                    await an.run_in_actor(
                         func,
                         name=f'actor_{i}',
                         **kwargs
@@ -337,7 +349,8 @@ async def test_some_cancels_all(num_actors_and_errs, start_method, loglevel):
 
         # should error here with a ``RemoteActorError`` or ``MultiError``
 
-    except first_err as err:
+    except first_err as _err:
+        err = _err
         if isinstance(err, BaseExceptionGroup):
             assert len(err.exceptions) == num_actors
             for exc in err.exceptions:
@@ -348,8 +361,8 @@ async def test_some_cancels_all(num_actors_and_errs, start_method, loglevel):
         elif isinstance(err, tractor.RemoteActorError):
             assert err.boxed_type == err_type
 
-        assert n.cancelled is True
+        assert an.cancelled is True
-        assert not n._children
+        assert not an._children
     else:
         pytest.fail("Should have gotten a remote assertion error?")
 
@@ -533,38 +546,123 @@ def test_cancel_via_SIGINT_other_task(
 
 async def spin_for(period=3):
     "Sync sleep."
+    print(f'sync sleeping in sub-sub for {period}\n')
     time.sleep(period)
 
 
-async def spawn():
+async def spawn_sub_with_sync_blocking_task():
-    async with tractor.open_nursery() as tn:
+    async with tractor.open_nursery() as an:
-        await tn.run_in_actor(
+        print('starting sync blocking subactor..\n')
+        await an.run_in_actor(
             spin_for,
             name='sleeper',
         )
+        print('exiting first subactor layer..\n')
 
 
+@pytest.mark.parametrize(
+    'man_cancel_outer',
+    [
+        False,  # passes if delay != 2
+
+        # always causes an unexpected eg-w-embedded-assert-err?
+        pytest.param(True,
+             marks=pytest.mark.xfail(
+                 reason=(
+                    'always causes an unexpected eg-w-embedded-assert-err?'
+                )
+            ),
+        ),
+    ],
+)
 @no_windows
 def test_cancel_while_childs_child_in_sync_sleep(
-    loglevel,
+    loglevel: str,
-    start_method,
+    start_method: str,
-    spawn_backend,
+    spawn_backend: str,
+    debug_mode: bool,
+    reg_addr: tuple,
+    man_cancel_outer: bool,
 ):
-    """Verify that a child cancelled while executing sync code is torn
+    '''
+    Verify that a child cancelled while executing sync code is torn
     down even when that cancellation is triggered by the parent
     2 nurseries "up".
-    """
+
+    Though the grandchild should stay blocking its actor runtime, its
+    parent should issue a "zombie reaper" to hard kill it after
+    sufficient timeout.
+
+    '''
     if start_method == 'forkserver':
         pytest.skip("Forksever sux hard at resuming from sync sleep...")
 
     async def main():
-        with trio.fail_after(2):
+        #
-            async with tractor.open_nursery() as tn:
+        # XXX BIG TODO NOTE XXX
-                await tn.run_in_actor(
+        #
-                    spawn,
+        # it seems there's a strange race that can happen
-                    name='spawn',
+        # where where the fail-after will trigger outer scope
+        # .cancel() which then causes the inner scope to raise,
+        #
+        # BaseExceptionGroup('Exceptions from Trio nursery', [
+        #   BaseExceptionGroup('Exceptions from Trio nursery',
+        #   [
+        #       Cancelled(),
+        #       Cancelled(),
+        #   ]
+        #   ),
+        #   AssertionError('assert 0')
+        # ])
+        #
+        # WHY THIS DOESN'T MAKE SENSE:
+        # ---------------------------
+        # - it should raise too-slow-error when too slow..
+        #  * verified that using simple-cs and manually cancelling
+        #    you get same outcome -> indicates that the fail-after
+        #    can have its TooSlowError overriden!
+        #  |_ to check this it's easy, simplly decrease the timeout
+        #     as per the var below.
+        #
+        # - when using the manual simple-cs the outcome is different
+        #   DESPITE the `assert 0` which means regardless of the
+        #   inner scope effectively failing in the same way, the
+        #   bubbling up **is NOT the same**.
+        #
+        # delays trigger diff outcomes..
+        # ---------------------------
+        # as seen by uncommenting various lines below there is from
+        # my POV an unexpected outcome due to the delay=2 case.
+        #
+        # delay = 1  # no AssertionError in eg, TooSlowError raised.
+        # delay = 2  # is AssertionError in eg AND no TooSlowError !?
+        delay = 4  # is AssertionError in eg AND no _cs cancellation.
+
+        with trio.fail_after(delay) as _cs:
+        # with trio.CancelScope() as cs:
+        # ^XXX^ can be used instead to see same outcome.
+
+            async with (
+                # tractor.trionics.collapse_eg(),  # doesn't help
+                tractor.open_nursery(
+                    hide_tb=False,
+                    debug_mode=debug_mode,
+                    registry_addrs=[reg_addr],
+                ) as an,
+            ):
+                await an.run_in_actor(
+                    spawn_sub_with_sync_blocking_task,
+                    name='sync_blocking_sub',
                 )
                 await trio.sleep(1)
+
+                if man_cancel_outer:
+                    print('Cancelling manually in root')
+                    _cs.cancel()
+
+                # trigger exc-srced taskc down
+                # the actor tree.
+                print('RAISING IN ROOT')
                 assert 0
 
     with pytest.raises(AssertionError):

tests/test_clustering.py

@@ -13,26 +13,24 @@ MESSAGE = 'tractoring at full speed'
 def test_empty_mngrs_input_raises() -> None:
 
     async def main():
-        with trio.fail_after(1):
+        with trio.fail_after(3):
             async with (
                 open_actor_cluster(
                     modules=[__name__],
 
                     # NOTE: ensure we can passthrough runtime opts
-                    loglevel='info',
+                    loglevel='cancel',
-                    # debug_mode=True,
+                    debug_mode=False,
 
                 ) as portals,
 
-                gather_contexts(
+                gather_contexts(mngrs=()),
-                    # NOTE: it's the use of inline-generator syntax
-                    # here that causes the empty input.
-                    mngrs=(
-                        p.open_context(worker) for p in portals.values()
-                    ),
-                ),
             ):
-                assert 0
+                # should fail before this?
+                assert portals
+
+                # test should fail if we mk it here!
+                assert 0, 'Should have raised val-err !?'
 
     with pytest.raises(ValueError):
         trio.run(main)

tests/test_legacy_one_way_streaming.py

@@ -235,10 +235,16 @@ async def cancel_after(wait, reg_addr):
 
 
 @pytest.fixture(scope='module')
-def time_quad_ex(reg_addr, ci_env, spawn_backend):
+def time_quad_ex(
+    reg_addr: tuple,
+    ci_env: bool,
+    spawn_backend: str,
+):
     if spawn_backend == 'mp':
-        """no idea but the  mp *nix runs are flaking out here often...
+        '''
-        """
+        no idea but the  mp *nix runs are flaking out here often...
+
+        '''
         pytest.skip("Test is too flaky on mp in CI")
 
     timeout = 7 if platform.system() in ('Windows', 'Darwin') else 4
@@ -249,12 +255,24 @@ def time_quad_ex(reg_addr, ci_env, spawn_backend):
     return results, diff
 
 
-def test_a_quadruple_example(time_quad_ex, ci_env, spawn_backend):
+def test_a_quadruple_example(
-    """This also serves as a kind of "we'd like to be this fast test"."""
+    time_quad_ex: tuple,
+    ci_env: bool,
+    spawn_backend: str,
+):
+    '''
+    This also serves as a kind of "we'd like to be this fast test".
 
+    '''
     results, diff = time_quad_ex
     assert results
-    this_fast = 6 if platform.system() in ('Windows', 'Darwin') else 3
+    this_fast = (
+        6 if platform.system() in (
+            'Windows',
+            'Darwin',
+        )
+        else 3
+    )
     assert diff < this_fast
 
 

tests/test_root_infect_asyncio.py

@@ -147,8 +147,7 @@ def test_trio_prestarted_task_bubbles(
         await trio.sleep_forever()
 
     async def _trio_main():
-        # with trio.fail_after(2):
+        with trio.fail_after(2 if not debug_mode else 999):
-        with trio.fail_after(999):
             first: str
             chan: to_asyncio.LinkedTaskChannel
             aio_ev = asyncio.Event()
@@ -217,32 +216,25 @@ def test_trio_prestarted_task_bubbles(
                         ):
                             aio_ev.set()
 
-    with pytest.raises(
-        expected_exception=ExceptionGroup,
-    ) as excinfo:
-        tractor.to_asyncio.run_as_asyncio_guest(
-            trio_main=_trio_main,
-        )
-
-    eg = excinfo.value
-    rte_eg, rest_eg = eg.split(RuntimeError)
-
     # ensure the trio-task's error bubbled despite the aio-side
     # having (maybe) errored first.
     if aio_err_trigger in (
         'after_trio_task_starts',
         'after_start_point',
     ):
-        assert len(errs := rest_eg.exceptions) == 1
+        patt: str = 'trio-side'
-        typerr = errs[0]
+        expect_exc = TypeError
-        assert (
-            type(typerr) is TypeError
-            and
-            'trio-side' in typerr.args
-        )
 
     # when aio errors BEFORE (last) trio task is scheduled, we should
     # never see anythinb but the aio-side.
     else:
-        assert len(rtes := rte_eg.exceptions) == 1
+        patt: str = 'asyncio-side'
-        assert 'asyncio-side' in rtes[0].args[0]
+        expect_exc = RuntimeError
+
+    with pytest.raises(expect_exc) as excinfo:
+        tractor.to_asyncio.run_as_asyncio_guest(
+            trio_main=_trio_main,
+        )
+
+    caught_exc = excinfo.value
+    assert patt in caught_exc.args

tractor/_clustering.py

@@ -55,10 +55,17 @@ async def open_actor_cluster(
         raise ValueError(
             'Number of names is {len(names)} but count it {count}')
 
-    async with tractor.open_nursery(
+    async with (
-        **runtime_kwargs,
+        # tractor.trionics.collapse_eg(),
-    ) as an:
+        tractor.open_nursery(
-        async with trio.open_nursery() as n:
+            **runtime_kwargs,
+        ) as an
+    ):
+        async with (
+            # tractor.trionics.collapse_eg(),
+            trio.open_nursery() as tn,
+            tractor.trionics.maybe_raise_from_masking_exc()
+        ):
             uid = tractor.current_actor().uid
 
             async def _start(name: str) -> None:
@@ -69,9 +76,8 @@ async def open_actor_cluster(
                 )
 
             for name in names:
-                n.start_soon(_start, name)
+                tn.start_soon(_start, name)
 
         assert len(portals) == count
         yield portals
-
         await an.cancel(hard_kill=hard_kill)

tractor/_context.py

@@ -101,6 +101,9 @@ from ._state import (
     debug_mode,
     _ctxvar_Context,
 )
+from .trionics import (
+    collapse_eg,
+)
 # ------ - ------
 if TYPE_CHECKING:
     from ._portal import Portal
@@ -942,7 +945,7 @@ class Context:
         self.cancel_called = True
 
         header: str = (
-            f'Cancelling ctx from {side.upper()}-side\n'
+            f'Cancelling ctx from {side!r}-side\n'
         )
         reminfo: str = (
             # ' =>\n'
@@ -950,7 +953,7 @@ class Context:
             f'\n'
             f'c)=> {self.chan.uid}\n'
             f'   |_[{self.dst_maddr}\n'
-            f'     >>{self.repr_rpc}\n'
+            f'     >> {self.repr_rpc}\n'
             # f'    >> {self._nsf}() -> {codec}[dict]:\n\n'
             # TODO: pull msg-type from spec re #320
         )
@@ -2025,10 +2028,8 @@ async def open_context_from_portal(
     ctxc_from_callee: ContextCancelled|None = None
     try:
         async with (
-            trio.open_nursery(
+            collapse_eg(),
-                strict_exception_groups=False,
+            trio.open_nursery() as tn,
-            ) as tn,
-
             msgops.maybe_limit_plds(
                 ctx=ctx,
                 spec=ctx_meta.get('pld_spec'),

tractor/_discovery.py

@@ -28,7 +28,10 @@ from typing import (
 from contextlib import asynccontextmanager as acm
 
 from tractor.log import get_logger
-from .trionics import gather_contexts
+from .trionics import (
+    gather_contexts,
+    collapse_eg,
+)
 from .ipc import _connect_chan, Channel
 from ._addr import (
     UnwrappedAddress,
@@ -87,7 +90,6 @@ async def get_registry(
             yield regstr_ptl
 
 
-
 @acm
 async def get_root(
     **kwargs,
@@ -253,9 +255,12 @@ async def find_actor(
         for addr in registry_addrs
     )
     portals: list[Portal]
-    async with gather_contexts(
+    async with (
-        mngrs=maybe_portals,
+        collapse_eg(),
-    ) as portals:
+        gather_contexts(
+            mngrs=maybe_portals,
+        ) as portals,
+    ):
         # log.runtime(
         #     'Gathered portals:\n'
         #     f'{portals}'

tractor/_portal.py

@@ -39,7 +39,10 @@ import warnings
 
 import trio
 
-from .trionics import maybe_open_nursery
+from .trionics import (
+    maybe_open_nursery,
+    collapse_eg,
+)
 from ._state import (
     current_actor,
 )
@@ -583,14 +586,13 @@ async def open_portal(
     assert actor
     was_connected: bool = False
 
-    async with maybe_open_nursery(
+    async with (
-        tn,
+        collapse_eg(),
-        shield=shield,
+        maybe_open_nursery(
-        strict_exception_groups=False,
+            tn,
-        # ^XXX^ TODO? soo roll our own then ??
+            shield=shield,
-        # -> since we kinda want the "if only one `.exception` then
+        ) as tn,
-        # just raise that" interface?
+    ):
-    ) as tn:
 
         if not channel.connected():
             await channel.connect()

tractor/_root.py

@@ -37,13 +37,7 @@ import warnings
 
 import trio
 
-from ._runtime import (
+from . import _runtime
-    Actor,
-    Arbiter,
-    # TODO: rename and make a non-actor subtype?
-    # Arbiter as Registry,
-    async_main,
-)
 from .devx import (
     debug,
     _frame_stack,
@@ -64,6 +58,7 @@ from ._addr import (
 )
 from .trionics import (
     is_multi_cancelled,
+    collapse_eg,
 )
 from ._exceptions import (
     RuntimeFailure,
@@ -102,7 +97,7 @@ async def maybe_block_bp(
     ):
         logger.info(
             f'Found `greenback` installed @ {maybe_mod}\n'
-            'Enabling `tractor.pause_from_sync()` support!\n'
+            f'Enabling `tractor.pause_from_sync()` support!\n'
         )
         os.environ['PYTHONBREAKPOINT'] = (
             'tractor.devx.debug._sync_pause_from_builtin'
@@ -197,9 +192,13 @@ async def open_root_actor(
     # read-only state to sublayers?
     # extra_rt_vars: dict|None = None,
 
-) -> Actor:
+) -> _runtime.Actor:
     '''
-    Runtime init entry point for ``tractor``.
+    Initialize the `tractor` runtime by starting a "root actor" in
+    a parent-most Python process.
+
+    All (disjoint) actor-process-trees-as-programs are created via
+    this entrypoint.
 
     '''
     # XXX NEVER allow nested actor-trees!
@@ -397,7 +396,7 @@ async def open_root_actor(
                 f'Registry(s) seem(s) to exist @ {ponged_addrs}'
             )
 
-            actor = Actor(
+            actor = _runtime.Actor(
                 name=name or 'anonymous',
                 uuid=mk_uuid(),
                 registry_addrs=ponged_addrs,
@@ -436,7 +435,8 @@ async def open_root_actor(
             # https://github.com/goodboy/tractor/pull/348
             # https://github.com/goodboy/tractor/issues/296
 
-            actor = Arbiter(
+            # TODO: rename as `RootActor` or is that even necessary?
+            actor = _runtime.Arbiter(
                 name=name or 'registrar',
                 uuid=mk_uuid(),
                 registry_addrs=registry_addrs,
@@ -471,18 +471,21 @@ async def open_root_actor(
                     '-> Opening new registry @ '
                     +
                     '\n'.join(
-                        f'@{addr}' for addr in reg_addrs
+                        f'{addr}' for addr in reg_addrs
                     )
                 )
             logger.info(f'{report}\n')
 
-            # start the actor runtime in a new task
+            # start runtime in a bg sub-task, yield to caller.
-            async with trio.open_nursery(
+            async with (
-                strict_exception_groups=False,
+                collapse_eg(),
-                # ^XXX^ TODO? instead unpack any RAE as per "loose" style?
+                trio.open_nursery() as root_tn,
-            ) as nursery:
 
-                # ``_runtime.async_main()`` creates an internal nursery
+                # XXX, finally-footgun below?
+                # -> see note on why shielding.
+                # maybe_raise_from_masking_exc(),
+            ):
+                # `_runtime.async_main()` creates an internal nursery
                 # and blocks here until any underlying actor(-process)
                 # tree has terminated thereby conducting so called
                 # "end-to-end" structured concurrency throughout an
@@ -490,9 +493,9 @@ async def open_root_actor(
                 # "actor runtime" primitives are SC-compat and thus all
                 # transitively spawned actors/processes must be as
                 # well.
-                await nursery.start(
+                await root_tn.start(
                     partial(
-                        async_main,
+                        _runtime.async_main,
                         actor,
                         accept_addrs=trans_bind_addrs,
                         parent_addr=None
@@ -540,7 +543,7 @@ async def open_root_actor(
                     raise
 
                 finally:
-                    # NOTE: not sure if we'll ever need this but it's
+                    # NOTE/TODO?, not sure if we'll ever need this but it's
                     # possibly better for even more determinism?
                     # logger.cancel(
                     #     f'Waiting on {len(nurseries)} nurseries in root..')

tractor/_rpc.py

@@ -765,7 +765,6 @@ async def _invoke(
             BaseExceptionGroup,
             BaseException,
             trio.Cancelled,
-
         ) as _scope_err:
             scope_err = _scope_err
             if (

tractor/_runtime.py

@@ -74,6 +74,9 @@ from tractor.msg import (
     pretty_struct,
     types as msgtypes,
 )
+from .trionics import (
+    collapse_eg,
+)
 from .ipc import (
     Channel,
     # IPCServer,  # causes cycles atm..
@@ -359,7 +362,7 @@ class Actor:
 
     def pformat(
         self,
-        ds: str = ':',
+        ds: str = ': ',
         indent: int = 0,
         privates: bool = False,
     ) -> str:
@@ -1471,17 +1474,18 @@ async def async_main(
         # parent is kept alive as a resilient service until
         # cancellation steps have (mostly) occurred in
         # a deterministic way.
-        async with trio.open_nursery(
+        root_tn: trio.Nursery
-            strict_exception_groups=False,
+        async with (
-        ) as root_nursery:
+            collapse_eg(),
-            actor._root_n = root_nursery
+            trio.open_nursery() as root_tn,
+        ):
+            actor._root_n = root_tn
             assert actor._root_n
 
             ipc_server: _server.IPCServer
             async with (
-                trio.open_nursery(
+                collapse_eg(),
-                    strict_exception_groups=False,
+                trio.open_nursery() as service_nursery,
-                ) as service_nursery,
                 _server.open_ipc_server(
                     parent_tn=service_nursery,
                     stream_handler_tn=service_nursery,
@@ -1605,7 +1609,7 @@ async def async_main(
                 # start processing parent requests until our channel
                 # server is 100% up and running.
                 if actor._parent_chan:
-                    await root_nursery.start(
+                    await root_tn.start(
                         partial(
                             _rpc.process_messages,
                             chan=actor._parent_chan,

tractor/_supervise.py

@@ -44,6 +44,7 @@ from ._runtime import Actor
 from ._portal import Portal
 from .trionics import (
     is_multi_cancelled,
+    collapse_eg,
 )
 from ._exceptions import (
     ContextCancelled,
@@ -326,9 +327,10 @@ class ActorNursery:
         server: IPCServer = self._actor.ipc_server
 
         with trio.move_on_after(3) as cs:
-            async with trio.open_nursery(
+            async with (
-                strict_exception_groups=False,
+                collapse_eg(),
-            ) as tn:
+                trio.open_nursery() as tn,
+            ):
 
                 subactor: Actor
                 proc: trio.Process
@@ -421,10 +423,10 @@ async def _open_and_supervise_one_cancels_all_nursery(
     # `ActorNursery.start_actor()`).
 
     # errors from this daemon actor nursery bubble up to caller
-    async with trio.open_nursery(
+    async with (
-        strict_exception_groups=False,
+        collapse_eg(),
-        # ^XXX^ TODO? instead unpack any RAE as per "loose" style?
+        trio.open_nursery() as da_nursery,
-    ) as da_nursery:
+    ):
         try:
             # This is the inner level "run in actor" nursery. It is
             # awaited first since actors spawned in this way (using
@@ -434,11 +436,10 @@ async def _open_and_supervise_one_cancels_all_nursery(
             # immediately raised for handling by a supervisor strategy.
             # As such if the strategy propagates any error(s) upwards
             # the above "daemon actor" nursery will be notified.
-            async with trio.open_nursery(
+            async with (
-                strict_exception_groups=False,
+                collapse_eg(),
-                # ^XXX^ TODO? instead unpack any RAE as per "loose" style?
+                trio.open_nursery() as ria_nursery,
-            ) as ria_nursery:
+            ):
-
                 an = ActorNursery(
                     actor,
                     ria_nursery,

tractor/trionics/__init__.py

@@ -31,7 +31,7 @@ from ._broadcast import (
 )
 from ._beg import (
     collapse_eg as collapse_eg,
-    maybe_collapse_eg as maybe_collapse_eg,
+    get_collapsed_eg as get_collapsed_eg,
     is_multi_cancelled as is_multi_cancelled,
 )
 from ._taskc import (

tractor/trionics/_beg.py

@@ -15,8 +15,9 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 '''
-`BaseExceptionGroup` related utils and helpers pertaining to
+`BaseExceptionGroup` utils and helpers pertaining to
-first-class-`trio` from a historical perspective B)
+first-class-`trio` from a "historical" perspective, like "loose
+exception group" task-nurseries.
 
 '''
 from contextlib import (
@@ -24,27 +25,84 @@ from contextlib import (
 )
 from typing import (
     Literal,
+    Type,
 )
 
 import trio
+# from trio._core._concat_tb import (
+#     concat_tb,
+# )
 
 
-def maybe_collapse_eg(
+# XXX NOTE
-    beg: BaseExceptionGroup,
+# taken verbatim from `trio._core._run` except,
+# - remove the NONSTRICT_EXCEPTIONGROUP_NOTE deprecation-note
+#   guard-check; we know we want an explicit collapse.
+# - mask out tb rewriting in collapse case, i don't think it really
+#   matters?
+#
+def collapse_exception_group(
+    excgroup: BaseExceptionGroup[BaseException],
 ) -> BaseException:
+    """Recursively collapse any single-exception groups into that single contained
+    exception.
+
+    """
+    exceptions = list(excgroup.exceptions)
+    modified = False
+    for i, exc in enumerate(exceptions):
+        if isinstance(exc, BaseExceptionGroup):
+            new_exc = collapse_exception_group(exc)
+            if new_exc is not exc:
+                modified = True
+                exceptions[i] = new_exc
+
+    if (
+        len(exceptions) == 1
+        and isinstance(excgroup, BaseExceptionGroup)
+
+        # XXX trio's loose-setting condition..
+        # and NONSTRICT_EXCEPTIONGROUP_NOTE in getattr(excgroup, "__notes__", ())
+    ):
+        # exceptions[0].__traceback__ = concat_tb(
+        #     excgroup.__traceback__,
+        #     exceptions[0].__traceback__,
+        # )
+        return exceptions[0]
+    elif modified:
+        return excgroup.derive(exceptions)
+    else:
+        return excgroup
+
+
+def get_collapsed_eg(
+    beg: BaseExceptionGroup,
+
+) -> BaseException|None:
     '''
-    If the input beg can collapse to a single non-eg sub-exception,
+    If the input beg can collapse to a single sub-exception which is
-    return it instead.
+    itself **not** an eg, return it.
 
     '''
-    if len(excs := beg.exceptions) == 1:
+    maybe_exc = collapse_exception_group(beg)
-        return excs[0]
+    if maybe_exc is beg:
+        return None
 
-    return beg
+    return maybe_exc
 
 
 @acm
-async def collapse_eg():
+async def collapse_eg(
+    hide_tb: bool = True,
+
+    # XXX, for ex. will always show begs containing single taskc
+    ignore: set[Type[BaseException]] = {
+        # trio.Cancelled,
+    },
+    add_notes: bool = True,
+
+    bp: bool = False,
+):
     '''
     If `BaseExceptionGroup` raised in the body scope is
     "collapse-able" (in the same way that
@@ -52,15 +110,58 @@ async def collapse_eg():
     only raise the lone emedded non-eg in in place.
 
     '''
+    __tracebackhide__: bool = hide_tb
     try:
         yield
-    except* BaseException as beg:
+    except BaseExceptionGroup as _beg:
-        if (
+        beg = _beg
-            exc := maybe_collapse_eg(beg)
-        ) is not beg:
-            raise exc
 
-        raise beg
+        if (
+            bp
+            and
+            len(beg.exceptions) > 1
+        ):
+            import tractor
+            if tractor.current_actor(
+                err_on_no_runtime=False,
+            ):
+                await tractor.pause(shield=True)
+            else:
+                breakpoint()
+
+        if (
+            (exc := get_collapsed_eg(beg))
+            and
+            type(exc) not in ignore
+        ):
+
+            # TODO? report number of nested groups it was collapsed
+            # *from*?
+            if add_notes:
+                from_group_note: str = (
+                    '( ^^^ this exc was collapsed from a group ^^^ )\n'
+                )
+                if (
+                    from_group_note
+                    not in
+                    getattr(exc, "__notes__", ())
+                ):
+                    exc.add_note(from_group_note)
+
+            # raise exc
+            # ^^ this will leave the orig beg tb above with the
+            # "during the handling of <beg> the following.."
+            # So, instead do..
+            #
+            if cause := exc.__cause__:
+                raise exc from cause
+            else:
+                # suppress "during handling of <the beg>"
+                # output in tb/console.
+                raise exc from None
+
+        # keep original
+        raise # beg
 
 
 def is_multi_cancelled(