You want to make sure that is is a trigger program, and to ensure that the lead score is above 100 and coming from a score of below 100 so I would recommend the smart list to be
Use All Filters
Data value change Attribute is Lead Score
New Value is>99
Previous Value score is less than 100
Filter Member of of engagement program is true
Change Engagement Stream Status: Paused
Create SFDC task, etc.