I did a reset yesterday. Now, I can't make any blueprints. I have 28 compendia and 29K science, but there's no button on the Workshop tab to make blueprints. Am I missing a technology? (I have everything up through and including Architecture.) I haven't managed to get any blueprints through trading - is that the missing element?
Yes, you indeed need the Physics technology to produce blueprints. From the faq:
Effects Enables Blueprint crafting
You had architecture, what only costs 42k science. Physics costs 50k science. Assuming you had not Physics yet researched, that is (/was) the problem.