add ArrayBuffer, ArrayBufferView, SharedArrayBuffer, and BackingStore to Rust JSG

Author: anonrig

src/rust/AGENTS.md

@@ -8,7 +8,7 @@
 
 | Crate                | Purpose                                                                                                |
 | -------------------- | ------------------------------------------------------------------------------------------------------ |
-| `jsg/`               | Rust JSG bindings: `Lock`, `Rc<T>`, `Resource`, `Struct`, `Type`, `Realm`, `FeatureFlags`, module registration |
+| `jsg/`               | Rust JSG bindings: `Lock`, `Rc<T>`, `Resource`, `Struct`, `Type`, `Realm`, `FeatureFlags`, module registration; V8 handle types including typed arrays, `ArrayBuffer`, `ArrayBufferView`, `SharedArrayBuffer`, `BackingStore` |
 | `jsg-macros/`        | Proc macros: `#[jsg_struct]`, `#[jsg_method]`, `#[jsg_resource]`, `#[jsg_oneof]`, `#[jsg_static_constant]` |
 | `jsg-test/`          | Test harness (`Harness`) for JSG Rust bindings                                                         |
 | `api/`               | Rust-implemented Node.js APIs; registers modules via `register_nodejs_modules()`                       |
@@ -31,4 +31,7 @@
 - **Tests**: inline `#[cfg(test)]` modules; JSG tests use `jsg_test::Harness::run_in_context()`
 - **FFI pointers**: functions receiving raw pointers must be `unsafe fn` (see `jsg/README.md`)
 - **Parameter ordering**: `&Lock` / `&mut Lock` must always be the first parameter in any function that takes a lock (matching the C++ convention where `jsg::Lock&` is always first). This applies to free functions, trait methods, and associated functions (excluding `&self`/`&mut self` receivers which come before `lock`).
+- **Method naming**: do not use `get_` prefixes on methods — e.g. `buf.backing_store()` not `buf.get_backing_store()`. Static constructors belong on the marker struct (`impl ArrayBuffer { fn new(...) }`) not on `impl Local<'_, ArrayBuffer>`.
+- **FFI naming**: instance methods on an existing handle use a `local_<type>_<method>` prefix (e.g. `local_array_buffer_byte_length`). Static constructors that create a new value do **not** use the `local_` prefix — name them `<type>_<method>` (e.g. `array_buffer_new_with_mode`, `array_buffer_maybe_new`, `backing_store_new_resizable`).
+- **FFI groups**: `v8.rs` `mod ffi`, `ffi.h`, and `ffi.c++` all use matching comment groups (e.g. `// Local<T>`, `// Local<Array>`, `// Local<TypedArray>`, `// Local<ArrayBuffer>`, `// Local<ArrayBufferView>`, `// Local<SharedArrayBuffer>`, `// BackingStore`, `// Unwrappers`, `// Global<T>`, `// FunctionCallbackInfo`). When adding new FFI functions, place them in the correct group in **all three files**. Do not scatter related functions across groups.
 - **Feature flags**: `Lock::feature_flags()` returns a capnp `compatibility_flags::Reader` for the current worker. Use `lock.feature_flags().get_node_js_compat()`. Flags are parsed once and stored in the `Realm` at construction; C++ passes canonical capnp bytes to `realm_create()`. Schema: `src/workerd/io/compatibility-date.capnp`, generated Rust bindings: `compatibility_date_capnp` crate.