Reject failed UTF-16 sizing queries before allocating the UTF-8 result
and preserve terminating-NUL accounting.
Validation: nine host-stub cases with 16-bit wchar_t; native Windows
execution remains unverified.
Provide a separate Flutter development shell from the existing locked
Nix input and document the application build commands.
Validation: locked environment/version probe; no native application
qualification is claimed.