-- play_loop.lua : realtime playback with repeat ON, held alive for keep_secs.
local keep_secs = 240

if reaper.GetSetRepeat(0) == 0 then
  reaper.Main_OnCommand(1068, 0)  -- Transport: Repeat ON
end
reaper.Main_OnCommand(1007, 0)    -- Transport: Play

local t0 = reaper.time_precise()
local function keepalive()
  if reaper.time_precise() - t0 < keep_secs then
    reaper.defer(keepalive)
  else
    reaper.OnStopButton()
  end
end
reaper.defer(keepalive)