California’s powerful coastal watchdog has suffered a major blow after the state Supreme Court unanimously ruled it overstepped its authority over a shoreline development . In a 7-0 ruling, the court sided with Shear Development and determined the California Coastal Commission had improperly asserted appellate jurisdiction over a long-running San Luis Obispo County housing project. The decision sharply limits the agency’s ability to block or restrict certain coastal construction already approved by local governments. In a 7-0 ruling, the court sided with Shear Development and determined the California Coastal Commission had improperly asserted appellate jurisdiction over a long-running San Luis Obispo County housing project. Los Angeles Times via Getty Images The high court’s ruling not only undercut the commission’s prior actions in the case but also established that courts—not the commission—should interpret local coastal programs without deferring to the agency.…