In this Henle edition of BWV817 there are slashes between the notes of the chords in bars 1, 2, 3. What does this signify? I don't think I've seen this symbol anywhere else in the book. The editorial notes don't comment on bars 2, 3 at all.
They're intended as visual aids to clarify the voices.
- In m. 1, it's a clarification that the top voice is dotted while the lower voice is not.
- In m. 2, it's to make clear there are three voices, with the lowest voice having originated in the bass staff.
- M. 3 has the lines for the same reason as m. 1.
There is another possibility. They may have been guide lines for the engraver that were mistakenly included in the engraving.
This is a slur.
As explained in the foreword to Henry Purcell: Suites, Lessons and Pieces for the Harpsichord (J&W Chester, London, 1919):
and that is indeed how it's played.