Tokens → list of {:head :body} / {:query} clauses. SX symbols for
constants and variables (case-distinguished). not(literal) in body
desugars to {:neg literal}. Nested compounds permitted in arg
position for arithmetic; safety analysis (Phase 3) will gate them.
Conformance harness wraps lib/guest/conformance.sh; produces
lib/datalog/scoreboard.{json,md}.
