runtime: complete own name/length descriptors on builtins (follow-on to closed #3143)

[proggeramlug]

Summary

Built-in functions and constructors are still missing own name / length data
properties across a wide swath of the standard library. Test262 verifyProperty
checks fail with "name should be an own property" / "length should be an own
property" on ~131 cases spanning ~25 categories.

This is a follow-on to the now-closed #3143 ("Built-in property descriptors &
.name/.length conformance"). That issue landed partial coverage, but a full
parity sweep shows the conformance is far from complete — many builtins still
lack the own name/length properties (with the spec-required
{writable:false, enumerable:false, configurable:true} descriptor shape).

Evidence

From a test262 + node-core parity sweep (2026-05-31): 131 failures with this
exact signature. Affected categories (top): Function (9), RegExp (6), Math (6),
Reflect (6), TypedArrayConstructors (6), NativeErrors (5), Date (5), Object (5),
plus single/double-digit hits across ArrayBuffer, AsyncFunction, BigInt,
DataView, Array, Map, Set, WeakMap, WeakSet, Promise, and more.

Representative cases:

• built-ins/Array/from/Array.from-name.js — "name should be an own property"
• built-ins/Array/from/Array.from_arity.js — "length should be an own property"
• built-ins/ArrayBuffer/isView/{name,length}.js
• built-ins/AsyncFunction/{instance-has-name,instance-length}.js
• built-ins/BigInt/asIntN/{name,length}.js, asUintN/{name,length}.js
• built-ins/Reflect/apply/{name,length}.js, defineProperty/{name,length}.js
• built-ins/DataView/{name,length}.js

Repro

// All of these should print the spec values; today the own-property lookup fails.
console.log(Object.getOwnPropertyDescriptor(Array.from, 'name'));   // {value:'from', writable:false, enumerable:false, configurable:true}
console.log(Object.getOwnPropertyDescriptor(BigInt.asIntN, 'length')); // length 2
console.log(Reflect.apply.name, Reflect.apply.length);

Why it's high-leverage

This is a single semantic (own name/length descriptors on builtins) that, once
generalized, clears ~131 failures at once. It also unblocks verifyProperty-based
assertions in many other categories that currently abort early on this check.

Suggested scope

Audit how .name/.length are installed on builtin function/constructor objects
(the mechanism #3143 introduced) and extend it to cover every builtin
function/constructor uniformly, with the correct descriptor attributes.

---

Filed from the parity-gap radar (scripts/parity_gap_report.py). Cluster: 131
failures, "name/length should be an own property".

[proggeramlug]

PR #3715 lands the constructor half: every built-in constructor (Date, Map, RegExp, DataView, BigInt, ArrayBuffer, the native errors, the TypedArray constructors, …) now has spec-correct own name/length data properties observable through the full protocol (getOwnPropertyDescriptor, hasOwnProperty method + direct .call, propertyIsEnumerable, getOwnPropertyNames, in, delete).

Two adjacent gaps remain out of scope and are tracked separately:

• Static methods (Array.from, Reflect.apply, Math.max, …) aren't reified as first-class function values yet (typeof Array.from === 'number') — Reify built-in prototype methods as first-class callable values (#2059 family) #3144.
• The test262 verifyProperty harness reaches builtins via Function.prototype.call.bind(Object.prototype.hasOwnProperty) (uncurry-this), which returns undefined even for plain objects — runtime: Function.prototype.call.bind(method) (uncurry-this) returns undefined — gates test262 verifyProperty harness #3716. This gates the whole harness independently of descriptors.