Interpreter-surface parity pass:

- Real error values: the seven standard error constructors are callable
  globals; instanceof works for Error types (a specific type matches
  itself and Error, never a sibling) plus Date/RegExp/Map/Set/Array/
  Object/Promise. Caught failures carry the name the equivalent real-JS
  failure would have — JSON.parse and invalid regex patterns are
  SyntaxError, unknown identifiers and TDZ access ReferenceError,
  assignment to a constant TypeError, a bad normalize form RangeError;
  anything without a specific analogue stays plain Error and internal
  class names never leak. JSON.parse failures now include the engine's
  position detail. Error values remain plain { name, message } data;
  the brand rides on a non-enumerable symbol, so serialization is
  unchanged and spread loses it like JS loses the prototype.
- Array splice/fill/copyWithin and keys/values/entries; string
  localeCompare/normalize/trimLeft/trimRight; regex failures now name
  the offending pattern or flags, the engine reason, and how to fix it.
- Sandbox values survive intra-sandbox checkpoints: Object.* helpers,
  coercions, and spread pass Date/RegExp/Map/Set through by reference
  (copyIn gained a preserving mode), so Object.values({d}).getTime()
  works. The host boundary — results, tool arguments, JSON.stringify —
  still serializes JSON forms exactly as documented.
- Console formatting is total and deep: NaN/Infinity print literally,
  nested sandbox values render their friendly forms, opaque references
  become in-place markers, cycles render [Circular]; console can no
  longer fail a program.
- maxOutputBytes lost its 32,000 default, completing uniform no-default
  limits: absent now means no truncation, for hosts that bound tool
  output themselves. Explicit values validate and truncate as before.