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newsfragments/230.removal.rst

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+Drop stream "shielding" support which was originally added to sidestep
+a cancelled call to ``.receive()``
+
+In the original api design a stream instance was returned directly from
+a call to ``Portal.run()`` and thus there was no "exit phase" to handle
+cancellations and errors which would trigger implicit closure. Now that
+we have said enter/exit semantics with ``Portal.open_stream_from()`` and
+``Context.open_stream()`` we can drop this implicit (and arguably
+confusing) behavior.