- `[ ]` means a concrete compatibility gap remains.

- Checked items do not promise complete ECMAScript edge-case parity; known differences are stated explicitly.

- Intentional boundaries are not listed as compatibility work.

- [x] Program results use JSON-like boundaries, with `undefined` and non-finite numbers normalized to `null`. Tool

arguments remain subject to their schema and the outbound-handling gap listed below.

- [x] Object literals with shorthand, computed string/number keys, and spread from plain data objects; `null` and

`undefined` are no-ops, while arrays are rejected.

- [ ] BigInt literals and in-interpreter BigInt arithmetic; BigInt remains invalid at JSON-like host boundaries.

- [ ] Symbol primitive values and symbol-keyed properties.

- [ ] Tagged-template calls.

- [ ] Getter and setter definitions in object literals.

- [x] Assignment to identifiers, unblocked plain-object fields, non-negative integer array indexes, and writable URL

fields.

- [x] Direct function declarations are hoisted in program and block statement lists.

- [ ] JavaScript-correct function scoping, hoisting, and redeclaration for accepted `var` declarations.

- [ ] Predeclare `let` and `const` bindings in every lexical scope, including program/block bodies, switch bodies, and

loop headers, so reads before initialization and self- or cross-referential initializers observe the JavaScript

temporal dead zone.

- [ ] Hoist function declarations accepted directly in switch cases.

- [ ] Array destructuring from supported non-array iterables: strings, Maps, Sets, and URLSearchParams.

- [ ] Stop automatically awaiting promise-returning string replacers; match JavaScript's synchronous callback-result

coercion.

- [ ] `this` in non-arrow CodeMode functions and callbacks.

- [ ] User-defined constructor calls.

- [ ] `Function.prototype.call`, `apply`, and `bind` for CodeMode functions.

- [x] `new` for Array, Object, Error types, Date, RegExp, Map, Set, URL, URLSearchParams, and Promise.

- [ ] Unary `void` and property deletion, including computed forms such as `delete object[key]`.

- [ ] Thenable assimilation; objects with a callable `then` field remain plain data.

- [x] Dotted tool names are canonicalized into namespace paths; a path can be both callable and a namespace, and the

last definition supplied for a canonical path wins.

- [x] Tool path segments may be named `constructor`, `prototype`, or `__proto__` because paths use inert Map keys.

- [ ] Reject `undefined` and non-finite numbers in outbound tool arguments before render-only and OpenAPI tools run;

retain null normalization for program results and JSON serialization.

- [ ] Tokenize and case-fold non-ASCII tool paths, descriptions, and queries for tool search.

- [x] Prototype traversal and mutation through `__proto__`, `constructor`, and `prototype` are blocked.

- [ ] Legal own data fields named `__proto__`, `constructor`, or `prototype` are rejected at JSON/tool boundaries and

cannot be created, read, or written in CodeMode; tool path segments with those names remain supported.

- [ ] `Object.is` for supported data values.

- [x] The `Array` constructor with or without `new`: `Array(a, b)` collects arguments and `Array(n)` creates a sparse

array of that length; invalid lengths throw `RangeError`. Iteration, spread, join, and JSON handle holes like

JavaScript, and host results normalize holes to `null`.

- [ ] Canonical array/string index parsing: a key such as `"01"` must remain an ordinary property key rather than

aliasing index `1`.

- [ ] `Array.prototype.sort` and `toSorted` must preserve trailing holes; they currently turn holes into own

`undefined` elements.

- [ ] Native argument coercion for supported String methods; for example, `includes(1)` and `slice("1")` currently

reject instead of coercing.

- [ ] `++` and `--` must use CodeMode numeric coercion and reject opaque runtime references; they currently call host

`Number(...)` directly.

- [ ] Unknown static members must read as `undefined` for feature detection; some currently appear callable or throw

during property access.

- [x] `JSON.parse` and `JSON.stringify` for supported data objects; the blocked data-key gap listed above still applies.

- [ ] `Date.prototype.toUTCString` and its `toGMTString` alias.

- [ ] Native one-argument Date coercion; unsupported boolean/object inputs currently become invalid dates instead of

being coerced.

- [ ] Native Date loose-equality and default primitive-coercion semantics.

- [x] Captures, safe named groups (blocked member names are omitted), match `.index`, and stateful global matching.

- [x] Integration with supported String methods, including function replacers.

- [ ] `hasIndices`, match `indices`, and `unicodeSets` metadata for the `d` and `v` flags.

- [ ] Set composition and relation methods: `union`, `intersection`, `difference`, `symmetricDifference`, `isSubsetOf`,

`isSupersetOf`, and `isDisjointFrom`.

- [x] Catchable user throws, runtime failures raised during interpreted evaluation, awaited tool failures, and awaited

tool-call-limit failures; parse/compile failures, cooperative timeout, and output bounding remain outside program

`catch`.

- [x] Source locations on unsupported-syntax diagnostics for JavaScript-shaped input; TypeScript transpilation may

shift them.

- [ ] Distinguish user-thrown failures from interpreter defects and explicit tool refusals from sanitized internal tool

failures; preserve those categories in caught errors, promise rejection handlers, and `Promise.allSettled`

reasons.