Prep masking `.aclose()` script for test suite

So we can parametrize in various toggles to `main()` including,
- `child_errors_mid_stream: bool` which now also drives whether an
  additional, and otherwise non-affecting, `_tn` is allocated in
  the `finite_stream_to_rent()` subtask, only in the early stream
  termination case does it seem to produce a masked outcome?
  * see surrounding notes within.
- `raise_unmasked: bool` to toggle whether the embedded unmasker fn
  will actually raise the masked user RTE; this enables demoing the
  masked outcomes via simple switch and makes it easy to wrap them
  as `pytest.xfail()` outcomes.

Also in support,
- use `.trionics.collapse_eg()` around the root tn to ensure when
  unmasking we can catch the EG-unwrapped RTE easily from a test.
- flip stream `msg` logs to `.debug()` to reduce console noise.
- tweak mod's script iface to report/trace unexpected non-RTEs.

examples/trio/send_chan_aclose_masks_beg.py

@@ -9,8 +9,10 @@ import tractor
 import trio
 
 
-log = tractor.log.get_logger(__name__)
+log = tractor.log.get_logger(
-tractor.log.get_console_log('info')
+    name=__name__
+)
+
 
 @cm
 def teardown_on_exc(
@@ -54,6 +56,7 @@ def teardown_on_exc(
 async def finite_stream_to_rent(
     tx: trio.abc.SendChannel,
     child_errors_mid_stream: bool,
+    raise_unmasked: bool,
 
     task_status: trio.TaskStatus[
         trio.CancelScope,
@@ -68,20 +71,41 @@ async def finite_stream_to_rent(
         # inside the child  task!
         #
         # TODO, uncomment next LoC to see the supprsessed beg[RTE]!
-        # tractor.trionics.maybe_raise_from_masking_exc(),
+        tractor.trionics.maybe_raise_from_masking_exc(
+            raise_unmasked=raise_unmasked,
+        ),
 
         tx as tx,  # .aclose() is the guilty masker chkpt!
-        trio.open_nursery() as _tn,
+
+        # XXX, this ONLY matters in the
+        # `child_errors_mid_stream=False` case oddly!?
+        # THAT IS, if no tn is opened in that case then the
+        # test will not fail; it raises the RTE correctly?
+        #
+        # -> so it seems this new scope somehow affects the form of
+        #    eventual in the parent EG?
+        tractor.trionics.maybe_open_nursery(
+            nursery=(
+                None
+                if not child_errors_mid_stream
+                else True
+            ),
+        ) as _tn,
     ):
         # pass our scope back to parent for supervision\
         # control.
-        task_status.started(_tn.cancel_scope)
+        cs: trio.CancelScope|None = (
+            None
+            if _tn is True
+            else _tn.cancel_scope
+        )
+        task_status.started(cs)
 
         with teardown_on_exc(
             raise_from_handler=not child_errors_mid_stream,
         ):
             for i in range(100):
-                log.info(
+                log.debug(
                     f'Child tx {i!r}\n'
                 )
                 if (
@@ -107,23 +131,31 @@ async def main(
     #   bug and raises.
     #
     child_errors_mid_stream: bool,
+
+    raise_unmasked: bool = False,
+    loglevel: str = 'info',
 ):
+    tractor.log.get_console_log(level=loglevel)
+
+    # the `.aclose()` being checkpoints on these
+    # is the source of the problem..
     tx, rx = trio.open_memory_channel(1)
 
     async with (
+        tractor.trionics.collapse_eg(),
         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,
+                raise_unmasked=raise_unmasked,
                 tx=tx,
             )
         )
         async for msg in rx:
-            log.info(
+            log.debug(
                 f'Rent rx {msg!r}\n'
             )
 
@@ -139,7 +171,25 @@ async def main(
                 tn.cancel_scope.cancel()
 
 
+# XXX, manual test as script
 if __name__ == '__main__':
-
+    tractor.log.get_console_log(level='info')
     for case in [True, False]:
-        trio.run(main, case)
+        log.info(
+            f'\n'
+            f'------ RUNNING SCRIPT TRIAL ------\n'
+            f'child_errors_midstream: {case!r}\n'
+        )
+        try:
+            trio.run(partial(
+                main,
+                child_errors_mid_stream=case,
+                # raise_unmasked=True,
+                loglevel='info',
+            ))
+        except Exception as _exc:
+            exc = _exc
+            log.exception(
+                'Should have raised an RTE or Cancelled?\n'
+            )
+            breakpoint()