How can you introduce a package, so that it is listed in
$Packages, without adding it to
Note that this question is concerned with defining a package when evaluating code, e.g. through evaluating a cell, rather than loading a package from a file.
This is useful if you want to add capabilities without introducing new "bare" symbols in any way -- they live in their own context and must be referenced through an explicit context, unless the user adds that context back to the context path.