AXON compiler frontend — lexer, parser, AST, epistemic type system, type checker, IR generator. Zero runtime dependencies. v0.21.0 promotes the v0.20.0 narrow cardinality gate to a FULL Cardinality propagation pass (Fase 38.x.f): new `pub(crate)` Cardinality enum + `infer_flow_tail_cardinality` walks every FlowStep variant, joins if/else branches, and detects disagreement. New error codes T9XX bilateral (D3 plural-output + singular-tail), T9YY stream_cardinality_mismatch (D5 spatial vs temporal), W003 cardinality_disagreement_in_branches (D6). v0.20.0 the narrow Retrieve Cardinality Gate (Fase 38.x.e). v0.19.3 Request Binding Contract source set (Fase 37.y). v0.19.0 Declared & Compile-Time-Typed Store Schema (Fase 38). v0.18.0 Request Binding Contract totality (Fase 37). v0.17.0 `in_memory` axonstore (Fase 36.x). v0.12.0 wire-format adapter. v0.11.0 Fase 32 REST. v0.10.0 type-driven wire. v0.9.0 HTTP. v0.2.0–v0.8.0 earlier cycles.