Hey everyone; I've been working on parts of the runner API recently, and part of that has included a shift of how composite inputs and outputs must be represented by the time a PipelineRunner begins to access them. I have a PR that completes this work within the Java SDK, but wanted to ensure that everyone agrees on the change and anything required on their end before I start fiddling with all of the runner internals. For anyone except current runner authors, this should be completely transparent; for current runner authors, I need a short code review but nothing else.
I've written a one-pager about what's changing; the link is at https://s.apache.org/beam-runner-composites or directly at https://docs.google.com/document/d/1_CHLnj1RFAGKy_MfR54XmixakYNmCnhGZLWmuDSMJ10/edit#heading=h.qlkikisrzqqf Thanks, Thomas
