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.
{
public:
    static constexpr auto name = Impl::name;
    static FunctionPtr create(ContextPtr) { return std::make_shared<FunctionStringHashFixedString>(); }
    String getName() const override
    {
        return name;
    }
    size_t getNumberOfArguments() const override { return 1; }
    DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
    {
        if (!isStringOrFixedString(arguments[0]))
            throw Exception("Illegal type " + arguments[0]->getName() + " of argument of function " + getName(),
                ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
        return std::make_shared<DataTypeFixedString>(Impl::length);
    }
    bool useDefaultImplementationForConstants() const override { return true; }