Function classify_source 

pub fn classify_source(source: &str) -> Result<Determinacy, ParseError>

Phase 0 (work/FINISH_INTERPRETER.md): classify the determinacy of a LOGOS program.

Parses source and runs the determinacy classifier over the parsed program. Pure analysis — no optimization, no codegen. Returns whether the program is in the determinate (Kahn-deterministic) or nondeterminate fragment, with the nondeterminism witnesses.