Which two variables primarily determine the behaviour of an automatic gain control (AGC) loop?

The behaviour of an AGC loop is characterized primarily by its threshold (the signal level at which AGC action begins to reduce gain) and its decay time (how quickly the gain returns to normal after the signal drops). For example, fast decay times are used for CW to recover between dots and dashes, while slow decay times are preferred for SSB to prevent background noise from surging between words. Options involving clipping, blanking, or slope describe noise reduction, limiters, or filter characteristics. These belong to entirely different circuits and do not dictate the core timing and trigger variables of an AGC loop.