Westfield’s planning board has refused to extend a construction permit for a proposed $4 billion data center, halting the project for now after months of opposition from residents and local activists. The Oct. 14 decision is a major setback for the project’s proponents. Former City Councilor Mary Ann Babinski welcomed the outcome, saying in a text message, “Oh what a relief it is. No bulldozers!” City Councilor Kristen Mello, an analytical chemist and prominent critic of the proposal, said developers could submit another proposal next July, when Westfield’s one-year moratorium on new data centers expires. Any future plan, she said, would need stronger protections for the city’s water supply. The board’s refusal to extend the permit does not rule out another attempt to build a data center in Westfield. For residents who opposed the current proposal, the decision creates time for city officials and the community to press for answers about how a future project could affect local water resources.