The relevant file is mongo/db/extension/host/load_extension.cpp where we take a list of extensionPaths and dynamically load each extension one-by-one.

Currently, we would allow you to load the same extension multiple times. We should reject it (fail startup with an error logline) if we attempt to do so.

We should not worry about trying to load the same .so file using different pathnames since we're modifying the parameter in SPM-4363 to just take extension names (see that design doc). In other words, this could be done by just doing a string compare of the path name.

You could add a unit test to load_extension_test.cpp, and you could add this test case to extensions_parameter.js