Went straight to what matters to me: data structures, or how they are defined ("Show me your tables"). And couldn't find any mention of anything beyond arrays and enums. Should one conclude that there are no typed unions, no structs, no objects?

Objects and structs are described in "Types" [1]. There are no typed unions currently (maybe I'll add them, not sure yet), but there are "Traits" [2].

[1] https://github.com/thomasmueller/bau-lang#types [2] https://github.com/thomasmueller/bau-lang#traits