How to properly seal the transition between basement wall framing and spray-foamed box joists?
When we insulate the joist boxes in apartment buildings or commercial buildings we are required to close the boxes over the foam with drywall or flame retardant foam board.  Since your job is for utility purposes here's my thoughts.  After you spray a couple of inches of foam into each box, cut measured pieces of foam board that will snugly fit above your wall, between the joists and up against the 1" rise of the sill plate behind the wall. Put a few dabs of construction adhesive on the edges and fit them into place.  This will do a couple of things for you. It will create a larger dead air space in your now insulated boxes, extra R-value and also seal the top of your wall against the foundation.  Smaller pieces can be glued in under the joists to complete the wall seal.  If you want to further seal and joints in the foam board, use some HVAC aluminum tape.