Ok, this clears up my confusion - we want to more generally improve this whole process :-D.

What I will do for right now, then, is fix this PR to expect a ``Blob`` argument rather than raw bytes, fix the failing style tests, and add a test of my own.

Slightly longer term will be trawling SO and looking into this broader technical issue.

(I also have a client plugin to figure out how to write, so I'll try to interleave these two tasks when my clock is running on GRIT.)

Thanks for the explanations, much appreciated!