some unmanaged tools break within interactive rez-env'd shell

For example, currently xdg-open breaks for me, which causes 'rez-context -g' to fail.

We need a general way to use a tool within a resolved environment if it is available in that env, otherwise fall back to the unresolved env. To do this, interactive rez-env sessions will have to store the pre-resolved env in a file - let's say, 'orig_environ.yaml' alongside the other tempfiles. Then, tools such as xdg-open could be run within this env, if not provided as a package tool in the rez'd env.

Start by tracing how interactive rez-env sessions create and manage their tempfiles, then follow the rez-context -g path that invokes xdg-open. Review how the proposed orig_environ.yaml could represent the pre-resolved environment, and define completion as unmanaged tools using the resolved environment when available and otherwise falling back to the unresolved one.

Written by the indexing model from the issue text.