Seriously cover all overrun cases

This actually caught further runtime bugs so it's gud i tried..
Add overrun-ignore enabled / disabled cases and error catching for all
of them. More or less this should cover every possible outcome when
it comes to setting `allow_overruns: bool` i hope XD

tests/test_context_stream_semantics.py

@@ -722,7 +722,9 @@ async def echo_back_sequence(
     ctx:  tractor.Context,
     seq: list[int],
     wait_for_cancel: bool,
-    msg_buffer_size: int | None = None,
+    allow_overruns_side: str,
+    be_slow: bool = False,
+    msg_buffer_size: int = 1,
 
 ) -> None:
     '''
@@ -737,12 +739,22 @@ async def echo_back_sequence(
     total_batches: int = 1000 if wait_for_cancel else 6
 
     await ctx.started()
+    # await tractor.breakpoint()
     async with ctx.open_stream(
         msg_buffer_size=msg_buffer_size,
-        allow_overruns=True,
+
+        # literally the point of this test XD
+        allow_overruns=(allow_overruns_side in {'child', 'both'}),
     ) as stream:
 
-        seq = list(seq)  # bleh, `msgpack`...
+        # ensure mem chan settings are correct
+        assert (
+            ctx._send_chan._state.max_buffer_size
+            ==
+            msg_buffer_size
+        )
+
+        seq = list(seq)  # bleh, msgpack sometimes ain't decoded right
         for _ in range(total_batches):
             batch = []
             async for msg in stream:
@@ -750,6 +762,9 @@ async def echo_back_sequence(
                 if batch == seq:
                     break
 
+                if be_slow:
+                    await trio.sleep(0.05)
+
                 print('callee waiting on next')
 
             for msg in batch:
@@ -763,13 +778,29 @@ async def echo_back_sequence(
     return 'yo'
 
 
+@pytest.mark.parametrize(
+    # aka the side that will / should raise
+    # and overrun under normal conditions.
+    'allow_overruns_side',
+    ['parent', 'child', 'none', 'both'],
+    ids=lambda item: f'allow_overruns_side={item}'
+)
+@pytest.mark.parametrize(
+    # aka the side that will / should raise
+    # and overrun under normal conditions.
+    'slow_side',
+    ['parent', 'child'],
+    ids=lambda item: f'slow_side={item}'
+)
 @pytest.mark.parametrize(
     'cancel_ctx',
     [True, False],
     ids=lambda item: f'cancel_ctx={item}'
 )
-def test_allow_overruns_stream(
+def test_maybe_allow_overruns_stream(
     cancel_ctx: bool,
+    slow_side: str,
+    allow_overruns_side: str,
     loglevel: str,
 ):
     '''
@@ -794,26 +825,35 @@ def test_allow_overruns_stream(
                 'callee_sends_forever',
                 enable_modules=[__name__],
                 loglevel=loglevel,
+
+                # debug_mode=True,
             )
-            seq = list(range(3))
+            seq = list(range(10))
             async with portal.open_context(
                 echo_back_sequence,
                 seq=seq,
                 wait_for_cancel=cancel_ctx,
+                be_slow=(slow_side == 'child'),
+                allow_overruns_side=allow_overruns_side,
             ) as (ctx, sent):
 
                 assert sent is None
 
                 async with ctx.open_stream(
-                    msg_buffer_size=1,
+                    msg_buffer_size=1 if slow_side == 'parent' else None,
-                    allow_overruns=True,
+                    allow_overruns=(allow_overruns_side in {'parent', 'both'}),
                 ) as stream:
-                    count = 0
+
-                    while count < 3:
+                    total_batches: int = 2
+                    for _ in range(total_batches):
                         for msg in seq:
-                            print(f'root tx {msg}')
+                            # print(f'root tx {msg}')
                             await stream.send(msg)
-                            await trio.sleep(0.1)
+                            if slow_side == 'parent':
+                                # NOTE: we make the parent slightly
+                                # slower, when it is slow, to make sure
+                                # that in the overruns everywhere case
+                                await trio.sleep(0.16)
 
                         batch = []
                         async for msg in stream:
@@ -822,8 +862,6 @@ def test_allow_overruns_stream(
                             if batch == seq:
                                 break
 
-                        count += 1
-
                 if cancel_ctx:
                     # cancel the remote task
                     print('sending root side cancel')
@@ -842,8 +880,49 @@ def test_allow_overruns_stream(
             # cancel the daemon
             await portal.cancel_actor()
 
+    if (
+        allow_overruns_side == 'both'
+        or slow_side == allow_overruns_side
+    ):
         trio.run(main)
 
+    elif (
+        slow_side != allow_overruns_side
+    ):
+
+        with pytest.raises(tractor.RemoteActorError) as excinfo:
+            trio.run(main)
+
+        err = excinfo.value
+
+        if (
+            allow_overruns_side == 'none'
+        ):
+            # depends on timing is is racy which side will
+            # overrun first :sadkitty:
+
+            # NOTE: i tried to isolate to a deterministic case here
+            # based on timeing, but i was kinda wasted, and i don't
+            # think it's sane to catch them..
+            assert err.type in (
+                tractor.RemoteActorError,
+                StreamOverrun,
+            )
+
+        elif (
+            slow_side == 'child'
+        ):
+            assert err.type == StreamOverrun
+
+        elif slow_side == 'parent':
+            assert err.type == tractor.RemoteActorError
+            assert 'StreamOverrun' in err.msgdata['tb_str']
+
+    else:
+        # if this hits the logic blocks from above are not
+        # exhaustive..
+        pytest.fail('PARAMETRIZED CASE GEN PROBLEM YO')
+
 
 @tractor.context
 async def sleep_forever(

tractor/_streaming.py

@@ -426,6 +426,10 @@ class Context:
         if remote_uid:
             return tuple(remote_uid)
 
+    @property
+    def cancelled_caught(self) -> bool:
+        return self._scope.cancelled_caught
+
     # init and streaming state
     _started_called: bool = False
     _started_received: bool = False
@@ -743,7 +747,7 @@ class Context:
         ):
             return err
 
-        raise err from None
+        raise err  # from None
 
     async def result(self) -> Any | Exception:
         '''