[codex] runtime descriptor metadata for Math and generators

[andrewtdiz]

Linked Issues

• Fixes runtime: builtin own-property descriptor attributes wrong + getOwnPropertyDescriptor returns undefined #4139
• Partially addresses runtime: Generator/AsyncGenerator prototype method descriptors + brand checks #4141

Behavior Cluster

This is a focused runtime descriptor cut for builtin reflective metadata:

• installs descriptor-visible Math own methods and constants with Node-compatible data-property attributes
• routes escaped Math.<method> reads through the real Math namespace object so method name/length descriptors remain observable
• treats Math, JSON, and Reflect as builtin global values so bare namespace reads lower through globalThis
• honors own Symbol.toStringTag values in Object.prototype.toString, covering generator constructor reflection
• keeps Generator and AsyncGenerator prototype descriptor coverage pinned with focused parity fixtures

Why Batched

#4139 and #4141 both fail in the same reflective surface: builtin own-property descriptors and intrinsic prototype metadata. The implementation path is shared across global namespace installation, object descriptor lookup, and codegen member reads, and the tests use the same node-suite/globals parity harness.

Tests Added

• test-parity/node-suite/globals/builtin-namespace-descriptors.ts
• test-parity/node-suite/globals/generator-prototype-descriptors.ts

Validation

• cargo build --release -p perry-runtime -p perry
• PERRY_NO_AUTO_OPTIMIZE=1 PERRY_ALLOW_UNIMPLEMENTED=1 target/release/perry compile --no-cache test-parity/node-suite/globals/builtin-namespace-descriptors.ts -o /tmp/perry_builtin_namespace_descriptors && /tmp/perry_builtin_namespace_descriptors
• PERRY_NO_AUTO_OPTIMIZE=1 PERRY_ALLOW_UNIMPLEMENTED=1 target/release/perry compile --no-cache test-parity/node-suite/globals/generator-prototype-descriptors.ts -o /tmp/perry_generator_prototype_descriptors && /tmp/perry_generator_prototype_descriptors
• PATH=/tmp/perry-node25-bin:$PATH PERRY_NO_AUTO_OPTIMIZE=1 PERRY_NO_CACHE=1 ./run_parity_tests.sh --suite node-suite --module globals --filter builtin-namespace-descriptors
• PATH=/tmp/perry-node25-bin:$PATH PERRY_NO_AUTO_OPTIMIZE=1 PERRY_NO_CACHE=1 ./run_parity_tests.sh --suite node-suite --module globals --filter generator-prototype-descriptors
• cargo test -p perry-runtime object
• cargo fmt --all -- --check
• git diff --check
• git diff --check HEAD
• ./scripts/check_file_size.sh

Known Limitations

• This does not attempt to close every builtin descriptor failure in runtime: builtin own-property descriptor attributes wrong + getOwnPropertyDescriptor returns undefined #4139; it covers the Math/global namespace slice and generator-related reflection covered by the new parity fixtures.
• Async-generator scheduling/order failures called out in runtime: Generator/AsyncGenerator prototype method descriptors + brand checks #4141 remain out of scope.
• The Math thunks added here are sufficient for descriptor-visible escaped method values, but this PR is not a full Math semantics audit.

Non-Goals

• No TypedArray constructor descriptor work.
• No primitive wrapper reflective brand-check work.
• No broad descriptor-table rewrite across all builtins.