sim-codec-javascript

Bounded, lossless ECMAScript 2026 Script and Module source frontend. It emits a neutral concrete tree with byte spans, trivia, lexical-goal and ASI evidence; it does not evaluate source or construct compiler IR.

The loadable codec/javascript lowers all accepted Script and Module syntax to stable javascript/* Expr forms. Its plain, located, and recursively located tree lanes encode lowered forms canonically and use the shared __sim_expr__ tagged fallback for expressions JavaScript cannot spell. JavascriptBuilder is the supported downstream extension seam: wrappers can reuse node and token lowering, add namespaced forms, and retain parent origins without copying the parser. Parser coverage is deliberately independent of executable support.

The frozen authority and evidence corpus identity live in src/lib.rs and grammar/corpus-manifest.txt. Test262 is an oracle, not vendored code or a blanket conformance claim.