gistfile1.rb

return hash.reduce({}) do |acc, kv|
  acc[id + kv[0]] = { 'key' => kv[0], 'value' => kv[1] }
  acc # You're explicitely returning acc so it used again by the next invocation of the block
end

########

return hash.each_with_object({}) do |kv, acc| # Argument order is switched
  acc[id + kv[0]] = { 'key' => kv[0], 'value' => kv[1] }
  # no need to explicitely return
end