Good news, I found the run as dropdown on the General page of the Job Step properties dialog, not the Advanced page like I saw in a screen shot online, but SQL Server Agent still can't run the job to read from a network share (with a UNC path).

Starting to be concerned because the user account with the highest permissions I have access to does not have change or delete permissions on the network share. I have demonstrated to myself that SQL Server Agent will run the job when the SSIS package is pointed to a local directory to read files. Would lack of delete or change permissions somehow prevent SQL Server Agent from reading?