COUNTERPROPOSAL: A group of lawmakers and activists largely from the vanguard of the city’s left gathered yesterday to push back against elements of the mayor’s budget proposal, which is being combed through by the City Council. Public Advocate Jumaane Williams, Brooklyn Borough President Antonio Reynoso and Council Members Lincoln Restler and Shahana Hanif, who both co-chair the newly streamlined Progressive Caucus, criticized City Hall’s plans to roll back a planned 3K expansion and require savings from most city agencies while sparing the NYPD. The People’s Plan, an alternative budget proposal endorsed by the elected officials in attendance, also criticized proposed cuts to library and CUNY funding.