New member for old question!
Square D meter panel "see attach SC8L125S" use as SFD service panel, its busbar as "attach JPG".
The panel electricity from utility has direct connection to busbar without a 125A main breaker to limit current from utility to busbar, and the 100A breaker is a feeder breaker to sub-panel.
Q1. For single structure SFD service meter panel, breaker plug-in on busbar to supply sub-panels or branch circuits
are consider as service disconnects or branch circuits?
Q2. Is NEC 230.71 apply to SFD?