diff --git a/tractor/_streaming.py b/tractor/_streaming.py
index 11a268a..6c57065 100644
--- a/tractor/_streaming.py
+++ b/tractor/_streaming.py
@@ -298,8 +298,9 @@ class MsgStream(ReceiveMsgStream, trio.abc.Channel):
         '''
         # if self._eoc:
         #     raise trio.ClosedResourceError('This stream is already ded')
-        # if self._ctx._error:
-        #     raise self._ctx._error
+
+        if self._ctx._error:
+            raise self._ctx._error  # from None
 
         await self._ctx.chan.send({'yield': data, 'cid': self._ctx.cid})
 
@@ -309,6 +310,10 @@ class Context:
     '''
     An inter-actor, ``trio`` task communication context.
 
+    NB: This class should never be instatiated directly, it is delivered
+    by either runtime machinery to a remotely started task or by entering
+    ``Portal.open_context()``.
+
     Allows maintaining task or protocol specific state between
     2 communicating actor tasks. A unique context is created on the
     callee side/end for every request to a remote actor from a portal.
@@ -370,20 +375,26 @@ class Context:
 
         Acts as a form of "relay" for a remote error raised
         in the corresponding remote callee task.
+
         '''
         self._error = unpack_error(msg, self.chan)
 
+        # TODO: tempted to **not** do this by-reraising in a
+        # nursery and instead cancel a surrounding scope, detect
+        # the cancellation, then lookup the error that was set?
         if self._scope_nursery:
 
             async def raiser():
-                __tracebackhide__ = True
-                raise self._error
+                raise self._error from None
 
-            if not self._scope_nursery.cancel_scope.cancel_called:
+            # from trio.testing import wait_all_tasks_blocked
+            # await wait_all_tasks_blocked()
+            if not self._scope_nursery._closed:  # type: ignore
                 self._scope_nursery.start_soon(raiser)
 
     async def cancel(self) -> None:
-        '''Cancel this inter-actor-task context.
+        '''
+        Cancel this inter-actor-task context.
 
         Request that the far side cancel it's current linked context,
         Timeout quickly in an attempt to sidestep 2-generals...
@@ -444,7 +455,7 @@ class Context:
     async def open_stream(
 
         self,
-        backpressure: bool = False,
+        backpressure: Optional[bool] = True,
         msg_buffer_size: Optional[int] = None,
 
     ) -> AsyncGenerator[MsgStream, None]:
@@ -555,7 +566,7 @@ class Context:
                     try:
                         self._result = msg['return']
                         break
-                    except KeyError:
+                    except KeyError as msgerr:
 
                         if 'yield' in msg:
                             # far end task is still streaming to us so discard
@@ -569,7 +580,10 @@ class Context:
                         # internal error should never get here
                         assert msg.get('cid'), (
                             "Received internal error at portal?")
-                        raise unpack_error(msg, self._portal.channel)
+
+                        raise unpack_error(
+                            msg, self._portal.channel
+                        ) from msgerr
 
         return self._result