:plug_halt — removes Plug.Conn.halt/1. Without halt, execution continues to
subsequent plugs and the action, so a surviving :plug_halt mutant means no test
depends on this plug halting.
halt(conn) # → conn
conn |> halt() # → connMatches halt written directly (Plug.Conn.halt(conn)), aliased, or bare-imported
(halt(conn), the form use Plug.Builder / use Plug.Router — or Phoenix's
use MyAppWeb, :controller — produces), and only Plug.Conn.halt/1; a halt at any
other arity is a different call and is left untouched.