This QResponse constructor attempts to eliminate all effects in this stream that aren't actually part of the response stream by eagerly evaluating the "first few" effects of the stream.
This QResponse constructor attempts to eliminate all effects in this stream that aren't actually part of the response stream by eagerly evaluating the "first few" effects of the stream. Examples of such effects are opening a quasar filesystem file, initiating a query to a connector, etc. Doing so allows us to provide a proper error response to clients instead of sending a Http OK and then failing to stream the response body because actually it turned out the file didn't exist after all.
The better fix for this problem would probably be to avoid constructing such processes (at least for use in the web layer) and instead make a distinction between the effects that create a stream and the effects that "run" the stream.
In the meantime, this constructor should mostly do the right thing if provided with such processes.