The change check: a cheap run in front of the real one

Sometimes you really do need five minutes and there's no event to listen for — a launch is live, or a page you don't own is moving fast and only its owner knows when. You can't trigger on an event you don't control. So do the next best thing: don't make the full run cheaper — make most runs not be full runs.

Split the routine into two stages.

Stage one: the check. Read one small thing that tells you whether anything changed — a status field, the last commit hash, a count of open items, a "last updated" timestamp. That's maybe 2,000 tokens and a one-word answer. Compare it to a value you saved last time. If it's the same, log "no change" and stop. If it's different, go on to stage two.

Stage two: the work. Only now does the Bot do the expensive thing — open the page fully, analyze it, write the summary, post the result.

Here's why it works, in numbers. A cheap check costs about $0.004 a run. Say the thing you're watching actually changes about six times a day — so 180 real changes a month, and the rest are "nothing happened":

No check:   8,640 full runs  x $0.046            = ~$397
With check: 8,640 checks      x $0.004  = ~$35
          +   180 full runs   x $0.046  = ~$8
                                   total = ~$43   (about 89% less)

Same five-minute reaction time. Roughly a ninth of the compute. (Six changes a day is an assumption — on a quiet page you save even more, on a busy one less.)

The instruction looks like this:

Every 5 minutes:

CHECK
Open [the page / repo / board]. Read ONLY [the status field / last
commit hash / count of open items / "updated" date]. Compare it to
the value saved in routines/state/<name>.txt. If it is the same, log
"no_change" and stop. Do not open anything else. Do not take a quick
look around.

WORK (only if it changed)
Save the new value to routines/state/<name>.txt, do the actual job,
and post the result in 5 lines or fewer.

Two lines are quietly load-bearing. "Read ONLY ..." keeps the check small — the whole saving comes from the check being cheap, so don't let it read the full page. And "Do not take a quick look around" matters more than it looks: without it, a capable Bot that's already on the page tends to explore, and exploring is a full run. You're paying for discipline here as much as logic. Say it plainly, and the cheap check stays cheap.