Walking down Eighth Avenue a few weeks ago, I made sure my backpack was fully zipped shut. Inside was a modest stash of pot, bought just an hour or so earlier. A friend knew someone in that world, and after an introduction, then a quiet, discreet meeting, I was on my way to the subway. Never before had I walked through Midtown Manhattan with it on my person. There were four cookies in vacuum-sealed pouches — “edibles” is the technical term — and then a few pinches of what was described as “herb.”