To reproduce, start present, navigate to localhost:3999 in your browser, and open a presentation. Then hit reload a bunch of times. For each reload, a new playground socket handler gets spun up, each of which permanently leaks a goroutine.

Hitting present with a SIGQUIT yields lots of these:

goroutine 52 [chan receive, 6 minutes]:
golang.org/x/tools/playground/socket.func·002()
    $GOPATH/src/golang.org/x/tools/playground/socket/socket.go:125 +0x10b
created by golang.org/x/tools/playground/socket.socketHandler
    $GOPATH/src/golang.org/x/tools/playground/socket/socket.go:131 +0x2b0

Note that in socketHandler.go line 125 there's a range loop reading from a channel that never gets closed.

Noticed because I added net/http/pprof to present for a demo and saw the goroutines profile number steadily increasing.