Interestingly, the interact command was added at changeset:

$ hg log -v --pager cat -r $(hg blame Lib/pdb.py | grep do_interact | awk -F : '{print $1}')
changeset:   66691:c2578a68879d
user:        Georg Brandl <georg@python.org>
date:        Sat Dec 04 11:20:26 2010 +0000
files:       Doc/library/pdb.rst Lib/pdb.py Misc/NEWS
description:
Add the "interact" pdb command from pdb++.


And the included documentation, added at that time, states (emphasis added by me):
Start an interative interpreter (using the code module) whose global namespace contains all the ***(global and local)*** names found in the current scope.


I can provide a test case for the patch when this issue is re-opened, unless someone else is willing to do it.