Update: after two days out with moderate winds, we had another day of (relatively) high winds, although the scary forecast wasn't matched by what we found on the water.
The repair seems to hold up fine (we also set a reef in the main before setting out, avoiding any lengthy periods with the jib not trimmed).
I simply ran one layer of tape on either side of the window along the split. The tape shows no sign of letting go anywhere, and it's nicely invisible, except where I trapped some bubbles. If it turns out that it won't hold across the split due to whatever bending happens there, then the next thing would be to double up the tape. It's pretty supple, though, and not at all crinkly like packing tape.
Curiously, when I put the tape away after making the repair, I found I already owned a roll

(Can't remember what I used it for.)