Add `.trionics.start_or_cancel()` test suite

Resolve #474 with a new `tests/trionics/test_taskc.py` (9
tests) covering the `trio.Nursery.start()` wrapper landed in
PR #464, incl. the `modden.runtime.progman.open_wks()` use
case dug out as a minimal repro.

Deats,
- the lossy `RuntimeError('child exited without calling
  task_status.started()')` only fires when the child absorbs
  its ambient cancel pre-`.started()` (graceful-teardown
  pattern); a well-behaved child surfaces `Cancelled` direct
  from `.start()` on `trio` 0.29 - verified empirically 1st.
- `test_sibling_err_not_masked_by_startup_rte`: the `modden`
  case; ONLY the root-cause sibling `ValueError` escapes the
  nursery with the wrapper vs. bare-`.start()`'s lossy
  riding-along startup-RTE noise.
- `test_pure_oob_cancel_not_morphed_to_rte`: plain ancestor
  `cs.cancel()` exits clean vs. bare's eg-wrapped RTE.
- `test_genuine_startup_rte_still_raised`: sans cancellation
  the protocol-bug RTE re-raises same as bare.
- `test_childs_own_rte_never_demoted_to_cancel`: exact-msg +
  `isinstance`-guard regression cover; a child's own
  `RuntimeError('never got started!')`/`RuntimeError(1234)`
  never demotes to a `Cancelled`.
- `test_started_value_and_args_passthru`: positional args,
  `name=` and `.started()`-value forwarding.

Also,
- `use_start_or_cancel=False` params pin upstream `trio`'s
  current lossy behaviour as wart-documentation: a break on
  a `trio` upgrade likely means new upstream porcelain and
  the wrapper deserves a re-audit.
- verified 0 flakes over 50 hammer runs + 2 impl mutations
  each caught by exactly the targeted tests.

Prompt-IO: ai/prompt-io/claude/20260702T161624Z_65bf9df5_prompt_io.md
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

ai/prompt-io/opencode/20260804T030309Z_65bf9df5_prompt_io.md

@@ -1,39 +0,0 @@
----
-model: openai/gpt-5.6-sol
-service: opencode
-session: moc-teardown-completion-20260804
-timestamp: 2026-08-04T03:03:09Z
-git_ref: 65bf9df5
-scope: code
-substantive: true
-raw_file: 20260804T030309Z_65bf9df5_prompt_io.raw.md
----
-
-## Prompt
-
-Patch Tractor's `maybe_open_context()` so the final consumer waits for
-resource `__aexit__()` completion and receives cleanup errors. Reuse
-`outcome.Outcome` for the exit result; use the smaller mutable
-`_CtxExit` holder if that makes the implementation simpler. Add and run
-the relevant existing unit tests, but do not commit or push the patch.
-After reviewing the result, simplify `_CtxExit` back to an optional
-exception because the success outcome carries no useful value.
-
-## Response summary
-
-Added an exception-backed completion handshake between
-`_Cache.run_ctx()` and the final `maybe_open_context()` consumer.
-Serialized consumer registration and final teardown under the per-key
-lock, preserving that lock for queued entrants. Added deterministic
-regressions for normal exit, cleanup errors, cancellation interactions,
-service-nursery cancellation, and teardown re-entry.
-
-## Files changed
-
-- `tractor/trionics/_mngrs.py` - publish and unwrap cached exit outcomes.
-- `tests/test_resource_cache.py` - cover completion and cancellation.
-
-## Human edits
-
-The user directed the final simplification from `outcome.Outcome` to an
-optional exception field. The patch remains uncommitted.

ai/prompt-io/opencode/20260804T030309Z_65bf9df5_prompt_io.raw.md

@@ -1,36 +0,0 @@
----
-model: openai/gpt-5.6-sol
-service: opencode
-timestamp: 2026-08-04T03:03:09Z
-git_ref: 65bf9df5
-diff_cmd: git diff HEAD~1..HEAD
----
-
-Implemented cached-context exit completion in
-`tractor.trionics.maybe_open_context()`.
-
-> `git diff HEAD~1..HEAD -- tractor/trionics/_mngrs.py`
-
-The generated implementation adds `_CtxExit`, whose `done` event
-publishes an `outcome.Outcome[None]`. `_Cache.run_ctx()` records either
-`Value(None)` or `Error(exc)` after the resource exit attempt. The final
-MOC consumer signals `no_more_users`, waits for completion under a
-shielded cancel scope, removes the per-key lock, and unwraps the outcome
-so ordinary cleanup failures are raised at the consumer boundary.
-`trio.Cancelled`, `KeyboardInterrupt`, and `SystemExit` continue through
-the service task rather than being converted into regular cleanup
-errors.
-
-> `git diff HEAD~1..HEAD -- tests/test_resource_cache.py`
-
-The generated regressions cover successful exit blocking, cleanup-error
-delivery, final-user cancellation, cancellation combined with a cleanup
-error, and service-nursery cancellation. The existing teardown re-entry
-test now uses explicit events instead of a ten-second cleanup sleep and
-asserts that the replacement resource is a fresh cache miss.
-
-Verification:
-
-`env PYTHONPATH="$PWD" /home/goodboy/repos/tractor/py313/bin/python -m pytest tests/test_resource_cache.py`
-
-Result: `16 passed in 8.37s`.

ai/prompt-io/opencode/README.md

@@ -1,22 +0,0 @@
-# AI Prompt I/O Log - OpenCode
-
-This directory tracks prompt inputs and model outputs for AI-assisted
-development using `opencode`.
-
-## Policy
-
-Prompt logging follows the [NLNet generative AI policy][nlnet-ai]. All
-substantive AI contributions are logged with:
-
-- Model name and version
-- Timestamps
-- The prompts that produced the output
-- Unedited model output (`.raw.md` files)
-
-[nlnet-ai]: https://nlnet.nl/foundation/policies/generativeAI/
-
-## Usage
-
-Entries are created by the prompt-io workflow. Human contributors remain
-accountable for all decisions. AI-generated content is never presented as
-human-authored work.

tests/test_log_sys.py

@@ -2,19 +2,16 @@
 `tractor.log`-wrapping unit tests.
 
 '''
-import logging
 from pathlib import Path
 import shutil
 from types import ModuleType
 
 import pytest
 import tractor
-import trio
 from tractor import (
     _code_load,
     log,
 )
-from tractor.ipc import _chan
 
 
 def test_root_pkg_not_duplicated_in_logger_name():
@@ -225,88 +222,6 @@ def test_add_log_level_pluggable():
             delattr(log.StackLevelAdapter, name.lower())
 
 
-@pytest.mark.parametrize(
-    'suppression',
-    [
-        'level',
-        'logger',
-        'global',
-    ],
-)
-def test_log_guard_skips_payload_formatting(
-    monkeypatch: pytest.MonkeyPatch,
-    suppression: str,
-):
-    '''
-    Suppressed transport logs must not render payloads.
-
-    The original hot-path guard compared only the effective logger
-    level. A logger disabled through its `Logger.disabled` flag or
-    the global `logging.disable()` threshold could therefore still
-    call `pformat()` before `Logger.isEnabledFor()` discarded the
-    record.
-
-    Exercise effective-level, per-logger, and global suppression
-    independently. A poisoned `_chan.pformat()` proves rendering is
-    skipped, while the fake transport proves `Channel.send()` still
-    transmits the original payload and traceback-hiding flag.
-
-    '''
-    sent: list[tuple[object, bool]] = []
-
-    class FakeTransport:
-        async def send(
-            self,
-            payload: object,
-            hide_tb: bool = False,
-        ) -> None:
-            sent.append((payload, hide_tb))
-
-    def fail_pformat(payload: object) -> str:
-        raise AssertionError(
-            f'suppressed log rendered payload: {payload!r}'
-        )
-
-    chan_log = log.get_logger(
-        name=f'guard_test.{suppression}',
-    )
-    std_log = chan_log.logger
-    orig_level: int = std_log.level
-    orig_disable: int = logging.root.manager.disable
-    transport_level: int = log.CUSTOM_LEVELS['TRANSPORT']
-
-    monkeypatch.setattr(_chan, 'log', chan_log)
-    monkeypatch.setattr(_chan, 'pformat', fail_pformat)
-    try:
-        logging.disable(logging.NOTSET)
-        std_log.setLevel(transport_level)
-
-        if suppression == 'level':
-            std_log.setLevel(logging.INFO)
-        elif suppression == 'logger':
-            monkeypatch.setattr(std_log, 'disabled', True)
-        else:
-            logging.disable(logging.CRITICAL)
-
-        assert not chan_log.isEnabledFor(transport_level)
-
-        transport = FakeTransport()
-        chan = _chan.Channel(transport=transport)
-        payload = object()
-
-        async def send_payload() -> None:
-            await chan.send(
-                payload,
-                hide_tb=True,
-            )
-
-        trio.run(send_payload)
-        assert sent == [(payload, True)]
-    finally:
-        std_log.setLevel(orig_level)
-        logging.disable(orig_disable)
-
-
 # TODO, moar tests against existing feats:
 # ------ - ------
 # - [ ] color settings?

tests/test_resource_cache.py

@@ -9,7 +9,6 @@ from typing import Awaitable
 
 import pytest
 import trio
-from trio.testing import wait_all_tasks_blocked
 import tractor
 from tractor.trionics import (
     maybe_open_context,
@@ -95,232 +94,6 @@ def test_resource_only_entered_once(key_on):
     trio.run(main)
 
 
-def test_last_moc_user_waits_for_resource_exit():
-    '''
-    Verify the final user cannot return before resource teardown.
-
-    Previously the final `maybe_open_context()` user only signalled
-    `_Cache.run_ctx()` through its `no_more_users` event. The user
-    then returned while the service task was still running the
-    resource's `__aexit__()`, so callers could observe stale external
-    state immediately after their `async with` block.
-
-    The resource sets `exit_started` before blocking on
-    `allow_exit`. The user task must remain inside MOC until the test
-    releases that deterministic checkpoint and `__aexit__()` sets
-    `exit_finished`.
-
-    '''
-    async def main():
-        exit_started = trio.Event()
-        allow_exit = trio.Event()
-        exit_finished = trio.Event()
-        user_returned = trio.Event()
-
-        @acm
-        async def open_resource():
-            try:
-                yield
-            finally:
-                exit_started.set()
-                await allow_exit.wait()
-                exit_finished.set()
-
-        async def use_resource():
-            async with maybe_open_context(open_resource):
-                pass
-
-            assert exit_finished.is_set()
-            user_returned.set()
-
-        async with (
-            tractor.open_root_actor(),
-            trio.open_nursery() as tn,
-        ):
-            tn.start_soon(use_resource)
-            await exit_started.wait()
-            assert not user_returned.is_set()
-            allow_exit.set()
-            await user_returned.wait()
-
-    trio.run(main)
-
-
-def test_moc_delivers_resource_exit_error():
-    '''
-    Verify a resource exit error reaches the final MOC user.
-
-    Previously `_Cache.run_ctx()` executed the cached resource's
-    `__aexit__()` after the final user had returned. An exit failure
-    therefore surfaced later through the actor service nursery rather
-    than at the user's `async with maybe_open_context()` boundary.
-
-    This resource raises a unique `ResourceExitError` during exit.
-    Catching that exact instance around MOC proves the service task
-    delivered the failure to the final user without replacing it.
-
-    '''
-    class ResourceExitError(Exception):
-        pass
-
-    exit_error = ResourceExitError('resource exit failed')
-
-    async def main():
-        @acm
-        async def open_resource():
-            yield
-            raise exit_error
-
-        async with tractor.open_root_actor():
-            with pytest.raises(ResourceExitError) as exc_info:
-                async with maybe_open_context(open_resource):
-                    pass
-
-            assert exc_info.value is exit_error
-
-    trio.run(main)
-
-
-def test_moc_final_user_cancellation_waits_for_exit():
-    '''
-    Verify final-user cancellation still waits for successful exit.
-
-    Previously cancellation escaped the final MOC user immediately
-    after it signalled `_Cache.run_ctx()`, leaving resource exit to
-    finish later in the actor service task. This violated the context
-    manager boundary even when cleanup itself succeeded.
-
-    The consumer cancels its own scope while holding the sole cached
-    resource. The resource sets `exit_finished` from its `finally`
-    block, and the consumer checks that event immediately after its
-    cancel scope catches `trio.Cancelled`. This proves MOC's
-    completion wait is shielded without suppressing the original
-    cancellation.
-
-    '''
-    async def main():
-        exit_finished = trio.Event()
-
-        @acm
-        async def open_resource():
-            try:
-                yield
-            finally:
-                exit_finished.set()
-
-        async with tractor.open_root_actor():
-            with trio.CancelScope() as cs:
-                async with maybe_open_context(open_resource):
-                    cs.cancel()
-                    await trio.sleep_forever()
-
-            assert cs.cancelled_caught
-            assert exit_finished.is_set()
-
-    trio.run(main)
-
-
-def test_moc_exit_error_masks_final_user_cancellation():
-    '''
-    Verify cleanup errors survive final-user cancellation.
-
-    A cancelled final user previously signalled `no_more_users` and
-    propagated `trio.Cancelled` before `_Cache.run_ctx()` completed
-    resource exit. If `__aexit__()` then failed, its error was
-    detached from the API call which caused teardown.
-
-    The consumer cancels its own scope at a deterministic checkpoint
-    inside MOC. Resource exit raises `ResourceExitError`; observing
-    that exact error outside the cancel scope proves MOC shields the
-    completion wait and applies normal context-manager masking, where
-    a cleanup failure replaces the active cancellation.
-
-    '''
-    class ResourceExitError(Exception):
-        pass
-
-    exit_error = ResourceExitError('resource exit failed')
-
-    async def main():
-        @acm
-        async def open_resource():
-            yield
-            raise exit_error
-
-        async with tractor.open_root_actor():
-            with pytest.raises(ResourceExitError) as exc_info:
-                with trio.CancelScope() as cs:
-                    async with maybe_open_context(open_resource):
-                        cs.cancel()
-                        await trio.sleep_forever()
-
-            assert exc_info.value is exit_error
-
-    trio.run(main)
-
-
-def test_moc_service_nursery_cancellation_completes_exit():
-    '''
-    Verify service-nursery cancellation cannot strand a final user.
-
-    `_Cache.run_ctx()` and an MOC consumer may share a
-    caller-provided service nursery. Cancelling that nursery
-    interrupts the service task's `no_more_users` wait and the
-    consumer body together. A shielded final-user wait would deadlock
-    if `run_ctx()` failed to publish completion while propagating its
-    own `trio.Cancelled`.
-
-    The outer task waits for resource entry, then cancels the exact
-    nursery containing both tasks. The resource shields one cleanup
-    checkpoint and sets `exit_finished`; observing both it and
-    `service_finished` proves cancellation propagated normally while
-    MOC's completion handshake terminated deterministically.
-
-    '''
-    async def main():
-        resource_entered = trio.Event()
-        exit_finished = trio.Event()
-        service_finished = trio.Event()
-        service_tn: trio.Nursery|None = None
-
-        @acm
-        async def open_resource():
-            try:
-                resource_entered.set()
-                yield
-            finally:
-                with trio.CancelScope(shield=True):
-                    await trio.lowlevel.checkpoint()
-                    exit_finished.set()
-
-        async def use_resource(tn: trio.Nursery):
-            async with maybe_open_context(
-                open_resource,
-                tn=tn,
-            ):
-                await trio.sleep_forever()
-
-        async def run_service():
-            nonlocal service_tn
-
-            async with trio.open_nursery() as tn:
-                service_tn = tn
-                tn.start_soon(use_resource, tn)
-
-            service_finished.set()
-
-        async with trio.open_nursery() as outer_tn:
-            outer_tn.start_soon(run_service)
-            await resource_entered.wait()
-            assert service_tn is not None
-            service_tn.cancel_scope.cancel()
-            await service_finished.wait()
-
-        assert exit_finished.is_set()
-
-    trio.run(main)
-
-
 @tractor.context
 async def streamer(
     ctx: tractor.Context,
@@ -775,52 +548,43 @@ def test_moc_reentry_during_teardown(
     loglevel: str,
 ):
     '''
-    Reproduce re-entry while an identical cached context exits.
+    Reproduce the piker `open_cached_client('kraken')` race:
 
-    - multiple tasks use the same `acm_func` with no kwargs,
-      producing an identical `ctx_key`;
-    - all users leave and the final user starts resource teardown;
-    - `_Cache.run_ctx()` removes the cached value and resource entry
-      before entering the resource's blocking `__aexit__()` body;
-    - a new task attempts to enter that same `ctx_key` during exit;
-    - the per-key lock keeps that entrant queued until exit
-      completes;
-    - the entrant then receives a fresh cache miss and resource.
+    - same `acm_func`, NO kwargs (identical `ctx_key`)
+    - multiple tasks share the cached resource
+    - all users exit -> teardown starts
+    - a NEW task enters during `_Cache.run_ctx.__aexit__`
+    - `values[ctx_key]` is gone (popped in inner finally)
+      but `resources[ctx_key]` still exists (outer finally
+      hasn't run yet bc the acm cleanup has checkpoints)
+    - old code: `assert not resources.get(ctx_key)` FIRES
 
-    Without teardown sharing the registration lock, re-entry could
-    race resource replacement while the prior generation was still
-    exiting. The final user could also return before that exit
-    completed.
-
-    The first resource generation signals `in_aexit` and waits on
-    `allow_aexit`. The re-entry task signals `reentry_started` and
-    blocks inside MOC; only after `wait_all_tasks_blocked()` confirms
-    that ordering does the coordinator release cleanup. The entrant
-    must then receive a fresh cache miss. `first_done` additionally
-    proves the first MOC user observed completed teardown before
-    returning.
+    This models the real-world scenario where `brokerd.kraken`
+    tasks concurrently call `open_cached_client('kraken')`
+    (same `acm_func`, empty kwargs, shared `ctx_key`) and
+    the teardown/re-entry race triggers intermittently.
 
     '''
     async def main():
         in_aexit = trio.Event()
-        allow_aexit = trio.Event()
-        reentry_started = trio.Event()
-        generation: int = 0
 
         @acm
         async def cached_client():
             '''
-            Simulate a no-argument `kraken.api.get_client()`.
+            Simulates `kraken.api.get_client()`:
+            - no params (all callers share one `ctx_key`)
+            - slow-ish cleanup to widen the race window
+              between `values.pop()` and `resources.pop()`
+              inside `_Cache.run_ctx`.
 
             '''
-            nonlocal generation
-
-            generation += 1
-            resource_generation: int = generation
             yield 'the-client'
-            if resource_generation == 1:
+            # Signal that we're in __aexit__ — at this
+            # point `values` has already been popped by
+            # `run_ctx`'s inner finally, but `resources`
+            # is still alive (outer finally hasn't run).
             in_aexit.set()
-                await allow_aexit.wait()
+            await trio.sleep(10)
 
         first_done = trio.Event()
 
@@ -834,25 +598,16 @@ def test_moc_reentry_during_teardown(
         async def reenter_during_teardown():
             '''
             Wait for the acm's `__aexit__` to start (meaning
-            the cached value is no longer available), then re-enter.
+            `values` is popped but `resources` still exists),
+            then re-enter — triggering the assert.
 
             '''
             await in_aexit.wait()
-
-            # Tell the coordinator this task is about to enter MOC.
-            # `Event.set()` is not a checkpoint. Though `async with`
-            # awaits MOC's `__aenter__()`, its async generator runs
-            # synchronously until the held per-key `lock.acquire()`
-            # actually suspends this task.
-            reentry_started.set()
             async with maybe_open_context(
                 cached_client,
             ) as (cache_hit, value):
-                assert not cache_hit
                 assert value == 'the-client'
 
-            await first_done.wait()
-
         with trio.fail_after(5):
             async with (
                 tractor.open_root_actor(
@@ -864,15 +619,5 @@ def test_moc_reentry_during_teardown(
             ):
                 tn.start_soon(use_and_exit)
                 tn.start_soon(reenter_during_teardown)
-                await reentry_started.wait()
-
-                # Wait until the re-entry task is queued on MOC's
-                # per-key lock while `_Cache.run_ctx()` remains
-                # blocked in the first generation's `__aexit__()`.
-                # Only then release cleanup, making the intended
-                # enter-during-sibling-exit ordering deterministic.
-                await wait_all_tasks_blocked()
-                assert not first_done.is_set()
-                allow_aexit.set()
 
     trio.run(main)

tractor/ipc/_chan.py

@@ -198,6 +198,9 @@ class Channel:
         # assert transport.raddr == addr
         chan = Channel(transport=transport)
 
+        # ?TODO, compact this into adapter level-methods?
+        # -[ ] would avoid extra repr-calcs if level not active?
+        #   |_ how would the `calc_if_level` look though? func?
         if log.at_least_level('runtime'):
             from tractor.devx import (
                 pformat as _pformat,
@@ -322,8 +325,6 @@ class Channel:
         '''
         __tracebackhide__: bool = hide_tb
         try:
-            if log.at_least_level('transport'):
-                # don't materialize the payload repr if not necessary
             log.transport(
                 '=> send IPC msg:\n\n'
                 f'{pformat(payload)}\n'

tractor/ipc/_transport.py

@@ -309,10 +309,7 @@ class MsgpackTransport(MsgTransport):
             log.transport(f'received header {size}')  # type: ignore
             msg_bytes: bytes = await self.recv_stream.receive_exactly(size)
 
-            if log.at_least_level('transport'):
-                log.transport(  # type: ignore
-                    f'received {msg_bytes}'
-                )
+            log.transport(f"received {msg_bytes}")  # type: ignore
             try:
                 # NOTE: lookup the `trio.Task.context`'s var for
                 # the current `MsgCodec`.

tractor/log.py

@@ -111,7 +111,9 @@ def at_least_level(
     if isinstance(level, str):
         level: int = CUSTOM_LEVELS[level.upper()]
 
-    return log.isEnabledFor(level)
+    if log.getEffectiveLevel() <= level:
+        return True
+    return False
 
 
 # TODO, compare with using a "filter" instead?

tractor/msg/_ops.py

@@ -306,12 +306,12 @@ class PldRx(Struct):
             ):
                 try:
                     pld: PayloadT = self._pld_dec.decode(pld)
-                    if log.at_least_level('runtime'):
-                        # don't materialize the payload repr if not necessary
                     log.runtime(
                         f'Decoded payload for\n'
-                            f'\n'
+                        # f'\n'
                         f'{msg}\n'
+                        # ^TODO?, ideally just render with `,
+                        # pld={decode}` in the `msg.pformat()`??
                         f'where, '
                         f'{type(msg).__name__}.pld={pld!r}\n'
                     )

tractor/runtime/_rpc.py

@@ -1003,15 +1003,17 @@ async def process_messages(
             task_status.started(loop_cs)
 
             async for msg in chan:
-                if log.at_least_level('transport'):
                 log.transport(   # type: ignore
                     f'IPC msg from peer\n'
                     f'<= {chan.aid.reprol()}\n\n'
 
-                        # TODO: pretty-printing structs is FRAGILE;
-                        # -[ ] add a non-raising log formatter with
-                        #      native-repr fallback before using
-                        #      `.msg.pretty_struct` here.
+                    # TODO: use of the pprinting of structs is
+                    # FRAGILE and should prolly not be
+                    #
+                    # avoid fmting depending on loglevel for perf?
+                    # -[ ] specifically `pretty_struct.pformat()` sub-call..?
+                    #   - how to only log-level-aware actually call this?
+                    # -[ ] use `.msg.pretty_struct` here now instead!
                     # f'{pretty_struct.pformat(msg)}\n'
                     f'{msg}\n'
                 )
@@ -1260,7 +1262,6 @@ async def process_messages(
                         log.exception(message)
                         raise RuntimeError(message)
 
-                if log.at_least_level('transport'):
                 log.transport(
                     'Waiting on next IPC msg from\n'
                     f'peer: {chan.aid.reprol()}\n'

tractor/trionics/_mngrs.py

@@ -198,16 +198,6 @@ async def gather_contexts(
 # Further potential examples of interest:
 # https://gist.github.com/njsmith/cf6fc0a97f53865f2c671659c88c1798#file-cache-py-L8
 
-class _CtxExit:
-    '''
-    Completion state for a cached context's shared exit.
-
-    '''
-    def __init__(self) -> None:
-        self.done = trio.Event()
-        self.error: Exception|None = None
-
-
 class _Cache:
     '''
     Globally (actor-processs scoped) cached, task access to
@@ -223,11 +213,7 @@ class _Cache:
     values: dict[Any,  Any] = {}
     resources: dict[
         Hashable,
-        tuple[
-            trio.Nursery,
-            trio.Event,
-            _CtxExit,
-        ],
+        tuple[trio.Nursery, trio.Event]
     ] = {}
     # nurseries: dict[int, trio.Nursery] = {}
     no_more_users: trio.Event|None = None
@@ -237,39 +223,19 @@ class _Cache:
         cls,
         mng,
         ctx_key: tuple,
-        ctx_exit: _CtxExit,
         task_status: trio.TaskStatus[T] = trio.TASK_STATUS_IGNORED,
 
     ) -> None:
-        entered: bool = False
-        try:
         async with mng as value:
-                entered = True
-                (
-                    _,
-                    no_more_users,
-                    _,
-                ) = cls.resources[ctx_key]
+            _, no_more_users = cls.resources[ctx_key]
             cls.values[ctx_key] = value
             task_status.started(value)
             try:
                 await no_more_users.wait()
             finally:
-                    cls.values.pop(ctx_key)
+                value = cls.values.pop(ctx_key)
                 cls.resources.pop(ctx_key)
 
-        except Exception as exc:
-            if not entered:
-                raise
-
-            # Deliver regular `__aexit__()` failures to the final
-            # consumer instead of raising into the service nursery.
-            ctx_exit.error = exc
-
-        finally:
-            if entered:
-                ctx_exit.done.set()
-
 
 class _UnresolvedCtx:
     '''
@@ -315,10 +281,9 @@ async def maybe_open_context(
         )
 
     # yielded output
+    # sentinel = object()
     yielded: Any = _UnresolvedCtx
     user_registered: bool = False
-    ctx_exit: _CtxExit|None = None
-    exit_error: Exception|None = None
 
     # Lock resource acquisition around task racing  / ``trio``'s
     # scheduler protocol.
@@ -335,6 +300,7 @@ async def maybe_open_context(
         ] = trio.StrictFIFOLock()
         header: str = 'Allocated NEW lock for @acm_func,\n'
     else:
+        await trio.lowlevel.checkpoint()
         header: str = 'Reusing OLD lock for @acm_func,\n'
 
     log.debug(
@@ -402,6 +368,7 @@ async def maybe_open_context(
             resources = _Cache.resources
             entry: tuple|None = resources.get(ctx_key)
             if entry:
+                service_tn, ev = entry
                 raise RuntimeError(
                     f'Caching resources ALREADY exist?!\n'
                     f'ctx_key={ctx_key!r}\n'
@@ -409,18 +376,12 @@ async def maybe_open_context(
                     f'task: {task}\n'
                 )
 
-            ctx_exit = _CtxExit()
-            resources[ctx_key] = (
-                service_tn,
-                trio.Event(),
-                ctx_exit,
-            )
+            resources[ctx_key] = (service_tn, trio.Event())
             try:
                 yielded: Any = await service_tn.start(
                     _Cache.run_ctx,
                     mngr,
                     ctx_key,
-                    ctx_exit,
                 )
             except BaseException:
                 # If `run_ctx` (wrapping the acm's `__aenter__`)
@@ -466,11 +427,6 @@ async def maybe_open_context(
             raise taskc
     else:
         # XXX, cached-entry-path
-        (
-            _,
-            _,
-            ctx_exit,
-        ) = _Cache.resources[ctx_key]
         _Cache.users[ctx_key] += 1
         user_registered = True
         log.debug(
@@ -489,17 +445,24 @@ async def maybe_open_context(
         )
 
     finally:
+        if lock.locked():
+            stats: trio.LockStatistics = lock.statistics()
+            owner: trio.Task|None = stats.owner
+            log.error(
+                f'Lock never released by last owner={owner!r} !?\n'
+                f'{stats}\n'
+                f'\n'
+                f'task={task!r}\n'
+                f'ctx_key={ctx_key!r}\n'
+                f'acm_func={acm_func}\n'
+
+            )
+
         if user_registered:
-            # Serialize user registration and teardown under the same
-            # per-key lock so no entrant can acquire a resource after
-            # its final user has committed to exiting it.
-            with trio.CancelScope(shield=True):
-                await lock.acquire()
-                try:
             _Cache.users[ctx_key] -= 1
 
-                    # If no consumers remain, keep entrants queued
-                    # until the cached context has completely exited.
+        if yielded is not _UnresolvedCtx:
+            # if no more consumers, teardown the client
             if _Cache.users[ctx_key] <= 0:
                 log.debug(
                     f'De-allocating @acm-func entry\n'
@@ -507,39 +470,19 @@ async def maybe_open_context(
                     f'acm_func={acm_func!r}\n'
                 )
 
-                        # XXX: if we're cancelled, the entry may
-                        # have never been entered since the nursery
-                        # task was killed.
+                # XXX: if we're cancelled we the entry may have never
+                # been entered since the nursery task was killed.
+                # _, no_more_users = _Cache.resources[ctx_key]
                 entry = _Cache.resources.get(ctx_key)
                 if entry:
-                            (
-                                _,
-                                no_more_users,
-                                ctx_exit,
-                            ) = entry
+                    _, no_more_users = entry
                     no_more_users.set()
 
-                        assert ctx_exit is not None
-                        await ctx_exit.done.wait()
-                        exit_error = ctx_exit.error
-
-                        # A queued entrant already holds a reference
-                        # to this lock. Keep it registered until that
-                        # task has acquired and released it.
-                        stats = lock.statistics()
-                        if not stats.tasks_waiting:
-                            maybe_lock = _Cache.locks.get(ctx_key)
-                            if maybe_lock is lock:
-                                _Cache.locks.pop(ctx_key)
-                            else:
-                                log.error(
-                                    f'Resource lock for {ctx_key} '
-                                    f'was replaced before teardown?'
+                maybe_lock = _Cache.locks.pop(
+                    ctx_key,
+                    None,
+                )
+                if maybe_lock is None:
+                    log.error(
+                        f'Resource lock for {ctx_key} ALREADY POPPED?'
                     )
-                finally:
-                    lock.release()
-
-        if exit_error is not None:
-            # Always re-raise a regular `__aexit__()` error at the
-            # final consumer's context boundary.
-            raise exit_error