Where is the documentation for version 1.0 of PostgreSQL wire protocol The current documentation refers only to version 3 of the wire protocol.
However, there is the following note in the documentation:

For descriptions of the earlier protocol versions, see previous releases of the PostgreSQL documentation

However, I can't find anything about previous versions of the wire protocol.
It is all in the Git repository, here is a link to the source. You can actually read the SGML source pretty well.