[sgbeal]

> That @ syntax is used in modern day Fossil too. Maybe that adds some extra overhead?

(Long-time Fossil dev here.)

The @ syntax is pre-processed, transformed to printf()-like calls, the destination of which depends on whether fossil is currently running (to simplify only slightly) from the CLI or as a CGI/server process.

That is: @ itself has no runtime costs, but does transform into calls which do have runtime costs. (printf() and its ilk aren't cheap!)