axon-frontend 0.5.0

AXON compiler frontend — lexer, parser, AST, epistemic type system, type checker, IR generator, compile-time checker. Zero runtime dependencies. v0.5.0 ships IRReturn.value_kind for Fase 18.d return runtime wiring (parser preserves literal-vs-reference intent for return values, mirror of let). v0.4.0 closed Fase 17 (let runtime). v0.3.0 closed Fase 14 (lossless lexing). v0.2.0 added Fase 13 typed channels.