Builders are buying lumber while floods in British Columbia limited supplies. Cash prices are also very high. Pricing service Random Lengths said its framing composite index, which tracks on-the-spot sales, has jumped 65% since October to $915. Last week’s jump of $129 was the biggest on record, eclipsing the jump of $124 in May, when lumber prices hit an all-time high.    Though lumber is traded in esoteric markets, two or four have become a proxy in the debate as to whether inflation will fade away with the lockdown. In June, Federal ...