How to revert launchctl PATH to defaults?
What ended up working to restore to default "factory presets" for me was to run:

sudo launchctl config user path /usr/bin:/bin:/usr/sbin:/sbin

This is not unlike the advice seen here (Set PATH variable so that it is detected in all applications, even outside terminal. (El Captain)). But some lingering questions remain:


Does this procedure restore what was already in the key-value pair of user path, or does it enact a new setting that would otherwise be empty?
Where, i.e., in what file or database, is this key-value stored?