Just days after being named permanent chief executive of Twitter, Dorsey is planning a series of cost-cutting maneuvers at the social networking company, including layoffs and halting a plan to expand the company’s San Francisco’s headquarters, according to three people familiar with the plans, who spoke on the condition of anonymity because the details are private. The plans to cut back both space and staffing are part of an effort to trim what many insiders see as an organization that has grown bloated — Twitter has more than 4,100 employees in more than 35 offices — over the past few years, these people said. Dorsey, 38, who also co-founded Twitter, had held the interim chief title since July 1 and has had time to assess the company’s prospects, strengths and weaknesses. While Twitter went public in 2013 in a wave of hype, its stock price has more recently fallen — at one point dropping below its $26 initial public offering price — as the company has struggled to attract new users. Reducing costs by reductions is always tough, but a better focus on execution and innovation will help them in the long run. Moving quickly once in the executive suite is a well-worn tactic by founder chief executives who return to their company after a stint away. Executives had just finished the discussion, these people said, and decided that trimming the fat from Twitter’s rapid expansion over the past two years would be necessary. Twitter’s stock had soared this week since Dorsey was named permanent chief, partly on Wall Street hopes that stability had entered the company’s executive suite.