Which command would be most suitable to be hooked in order to preprocess input before it is passed to TeX?
Input file:
\begin{document}
\input{a}
\end{document}
Seen by TeX (after a file a_pp.tex has been created):
\begin{document}
\input{a_pp}
\end{document}
What about \include, \bibliography, or even other means of including files?
Note that the preprocessing is to be applied only to files that are interpreted/compiled by TeX directly, not to files that are read and parsed by some macro.
This is to move towards Forward-inverse search using SyncTeX with the precison of a single word.