https://github.com/ClickHouse/ClickHouse/blob/9a48cf0da8badfc5f3da08611eb44961aa28e3f6/src/Functions/FunctionsHashing.h#L669-L671

There's a call to `blake3_free_char_pointer` that passes ownership of the pointer back to Rust (which then frees the memory), then there's a call to `std::string`'s constructor that accepts that now-freed pointer.
#if !USE_BLAKE3
    [[noreturn]] static void apply(const char * begin, const size_t size, unsigned char* out_char_data)
    {
        UNUSED(begin);
        UNUSED(size);
        UNUSED(out_char_data);
        throw Exception(ErrorCodes::SUPPORT_IS_DISABLED, "BLAKE3 is not available. Rust code or BLAKE3 itself may be disabled.");
    }
    #else
    static void apply(const char * begin, const size_t size, unsigned char* out_char_data)
    {
        #if defined(MEMORY_SANITIZER)
            auto err_msg = blake3_apply_shim_msan_compat(begin, safe_cast<uint32_t>(size), out_char_data);
            __msan_unpoison(out_char_data, length);
        #else
            auto err_msg = blake3_apply_shim(begin, safe_cast<uint32_t>(size), out_char_data);
        #endif
        if (err_msg != nullptr)
        {
            auto err_st = std::string(err_msg);
            blake3_free_char_pointer(err_msg);
            throw Exception("Function returned error message: " + std::string(err_msg), ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
        }
    }
    #endif
};
template <typename Impl>
class FunctionStringHashFixedString : public IFunction