The strangest North American lumber market in memory keeps getting stranger.  Canfor Corp., one of North America’s biggest lumber producers, said last week that it will shift to a four-day workweek at most of its 11 mills in British Columbia and Alberta starting April 4; not because of inadequate demand, but because it’s run out of room to pile the boards that customers are ordering at a startling rate.  “We are experiencing extreme supply chain challenges,” Don Kayne, chief executive of Vancouver-based Canfor, said in a press release on March 31. “It ...