-- lua/claim_job.lua
-- Atomically claim a job from waiting queues (priority + FIFO/LIFO buckets, then legacy wait) and move to active.
-- KEYS[1..n-1] = wait lists in claim order (RPOP from each), KEYS[n] = active_key
local n = #KEYS
local active_key = KEYS
for i = 1, n - 1
return nil