Added

• Added the maxAge attribute to the CookieInit dictionary in web-sys,
  matching the current Cookie Store API specification.
  #5169

• The js-sys futures codegen opt-in can now also be enabled via the
  WASM_BINDGEN_USE_JS_SYS=1 environment variable, in addition to
  --cfg=wasm_bindgen_use_js_sys. This works on stable when --target
  is in use, where Cargo does not propagate the cfg to host proc-macros.
  #5164

Changed

• JsOption<T> now treats only undefined as empty, aligning it with
  TypeScript's strict T | undefined semantics and with Option<T>'s wire
  shape (None ↔ undefined). Previously is_empty, as_option,
  into_option, unwrap, expect, unwrap_or_default, and
  unwrap_or_else treated both null and undefined as absent; JS null
  is now a distinct present value. The impl<T> UpcastFrom<Null> for JsOption<T> is removed (Undefined still models absence), and the
  Debug/Display absent placeholder changed from "null" to
  "undefined". Code relying on null → None should return undefined
  from the JS side, or check explicitly with
  val.as_option().filter(|v| !v.is_null()).
  #5170

Fixed

• Removed invalid js_sys::Array<T> to js_sys::ArrayTuple<(...)> upcasts.
  ArrayTuple encodes a fixed tuple arity, while a plain JavaScript array does
  not prove that arity statically.

• Fixed incorrect variance in &mut reference upcasting. &mut T upcasts
  were covariant in the pointee, so a &mut T could be widened to a &mut
  of a supertype and used to write back a value the original type would not
  accept, leaving a reference whose static type no longer matches the value
  it points to. Mutable references are now invariant in their pointee:
  &mut T only upcasts to &mut Target when both Target: UpcastFrom<T>
  and T: UpcastFrom<Target> hold. This rejects the invalid widening but is
  a breaking change for callers that relied on widening &mut references.
  #5176

• Fixed WASI targets (wasm32-wasip1/wasm32-wasip2) emitting unresolved
  __wbindgen_placeholder__ imports, which broke component linking. The
  codegen and runtime gates now exclude target_os = "wasi" (restoring the
  pre-0.2.115 stub behavior), including the panic = "unwind" paths in
  wasm-bindgen-futures.
  #5175

• Fixed a panic ("Unhandled load width 8") in the descriptor interpreter when
  processing -Cinstrument-coverage-instrumented modules, unblocking
  cargo llvm-cov --target wasm32-unknown-unknown for crates whose describe
  helpers get instrumented.
  #5179

• Fixed main silently never running on wasm64 for bin crates.
  #5181