\item[Correct interoperation] the developer must adhere to the \gls{API} or communication protocols between components. \Cref{sec_t4t:codesize,sec_t4t:resourcerich} show that communication requires some 17\% of \gls{PRS} and \gls{PWS} code, so around 100 \gls{SLOC}. \Cref{sec_t4t:Communication} discusses the complexity of writing this distributed communication code.
\item[Maintaining type safety] is a key element of the semantic friction encountered in multi-language stacks, and crucial for correctness. The developer must maintain type safety across a range of very different languages and diverse type systems, with minimal tool support. We show an example where \gls{PRS} loses type safety over the network layer (\Cref{sec_t4t:typesafety}).
\item[Managing multiple failure modes] different components may have different failure modes, and these must be coordinated. \Cref{sec_t4t:NetworkManagement} outlines how \gls{PRS} and \gls{PWS} use heartbeats to manage failures.
\item[Correct interoperation] the developer must adhere to the \gls{API} or communication protocols between components. \Cref{sec_t4t:codesize,sec_t4t:resourcerich} show that communication requires some 17\% of \gls{PRS} and \gls{PWS} code, so around 100 \gls{SLOC}. \Cref{sec_t4t:Communication} discusses the complexity of writing this distributed communication code.
\item[Maintaining type safety] is a key element of the semantic friction encountered in multi-language stacks, and crucial for correctness. The developer must maintain type safety across a range of very different languages and diverse type systems, with minimal tool support. We show an example where \gls{PRS} loses type safety over the network layer (\Cref{sec_t4t:typesafety}).
\item[Managing multiple failure modes] different components may have different failure modes, and these must be coordinated. \Cref{sec_t4t:NetworkManagement} outlines how \gls{PRS} and \gls{PWS} use heartbeats to manage failures.