Revert three commits:

Remove a needless comment. (f00d4a58fa0d508ccc036011a2a294786c027bbc)
Rename "Builder.Build" to "Builder.Exec". (7a9541238869fb0a57dae3ea03ec9002422df3b3)
"Builder" is called by "Agent". (7161e2c0d9dff6479335b4de0ff16705119d0289)