If the ebullience surrounding every squeak made by the San Francisco Symphony last Friday and Saturday is any measure, the orchestra's summer season is in fine hands. On the podium for much of the month has been Michael Francis, and waiting in the wings pianists Valentina Lisitsa and Sara Davis Buechner, all to dazzle and command in their own ways. About which more in a moment. Summer concerts are a special art and a fine test for the temperament and ability of musicians. While accuracy and sight-reading abilities reflect the latter, there is a special dimension of celebration and showmanship involved, and the treacherous challenge to popularize without diminishing. So it is a delight to report that the programs I attended in Davies Hall sported no colored lights, no floral wreaths, trotted out no talkative or, worse, awkward masters of ceremony, and contained no "special occasion" works of dubious provenance. Just classic music, and very well played it was. Remarkably so, with what must have been little rehearsal.