i am not so long with AOLserver to know this. The documentation section mentioning the purge of global Tcl variables was not changed for the last 17 years [1] (i.e. early 2001). One of the oldest AOLserver article from 2000 mentions already nsv as an instrument to share global variables [2].
Nevertheless, i fully trust Andrew's historical explanation about the intention of the original design. This shows, that this aspects of the performance mode are broken since at least 17 years and nobody has missed it. My suggestion is either to remove the ::tcl_url2file global variable, or to "do it right", including handling of host-node mappings etc. Currently, i personally would have time for just the first option.
-g
[1] https://github.com/openacs/openacs-core/blame/master/packages/acs-core-docs/www/xml/developers-guide/programming-with-aolserver.xml#L46
[2] http://www.tldp.org/LDP/LG/issue58/washington.html