/// Runtime handle shim for wasm32.
///
/// On wasm32 there is no multi-thread Tokio runtime, but
/// `tokio_with_wasm` provides async scheduling through browser APIs.
/// `try_current()` returns `Ok` so downstream code that stores the
/// handle in `Option<Handle>` gets `Some` and never sees a spurious
/// "no runtime" path.
;
/// Error type kept for API compatibility (never actually returned on wasm32).
;