ShadowRealm full test262 conformance

Date: 2026-06-25 Area: engine

Completes built-ins/ShadowRealm test262 conformance (64/64) on top of ADR 0073, which scoped four cases out. Two were deliberate divergences this change reverses for spec conformance; the other two were plain bugs.

eval in child realms (reversing the no-eval boundary). SetDefaultGlobalBindings installs eval on a realm's global object, so a spec-conformant ShadowRealm child global exposes it. ADR 0073 omitted it to honor the no-eval default, but ShadowRealm is already an explicit dynamic-evaluation capability (evaluate / importValue). The child realm now mirrors the creating realm: when — and only when — the creating realm exposes an own eval, the child gets its own realm-bound eval that evaluates in the child realm, so isolation holds and a host without eval (the default) still yields a child without eval.

Shared Symbol registry (reversing the per-realm registry). The GlobalSymbolRegistry is one per agent (ES2026 §20.4.2.2): every realm in a thread — the main realm, ShadowRealm child realms, and $262.createRealm realms — shares it, so Symbol.for(key) returns the same symbol across realms and Symbol.keyFor observes it. It is a thread-scoped store owned by the first TGocciaGlobalSymbol created in the thread; because child realms are torn down before their creator, the owner outlives every sharer and frees it at teardown. The garbage collector is a thread singleton, so registered symbols live on the shared heap regardless of which realm created them.

Bug fixes. A wrapped function's length now carries +∞ — CopyNameAndLength may yield +∞, which an integer arity cannot represent, so the wrapper defines length as the Number L directly. A static early error in evaluate (e.g. assigning to arguments in a strict body) is now a caller-realm SyntaxError, validated before evaluation rather than conflated with a runtime abrupt completion — which §3.1.3 still wraps as a caller-realm TypeError, including a runtime SyntaxError thrown by a nested eval.