On Monday morning, Korea's KOSPI fell 7.9% — one of its worst sessions in years. Our engine sealed its daily decisions a few hours later. The sealed record shows what it believed at that moment: "Asia +0.35% overnight — supportive backdrop."
Asia was not up 0.35%. Asia was on fire. Our engine was reading Friday.
This is the story of that bug, because publishing our misses is the product.
What went wrong. Our regime engine watches Asian markets through U.S.-listed ETFs that track Japan, Korea, Taiwan, and China. To avoid look-ahead bias — accidentally using information that wasn't available yet — the pipeline only consumed completed daily bars for those ETFs. But those ETFs trade on U.S. hours. At our seal time (before the U.S. open), their most recent completed bar was Friday's U.S. close. Monday's Korean session — which had already finished hours earlier, in plain sight of anyone with a phone — didn't exist yet in the data our engine allowed itself to see. A rule built to prevent cheating ended up preventing seeing.
What we did that day. The seal stayed sealed — we never revise a published record. Instead, 46 minutes before the U.S. open, we appended a labeled addendum to the day's report: here's what Asia actually did, here's what our engine believed, and no, we did not change its decisions. Then we fixed the pipeline overnight: the Asia signal now uses same-day snapshots at seal time, falling back per-ticker (with an honest label) when no fresh print exists. In a replay of that Monday, the new logic reads Korea at −7.53% instead of −0.67% — the signal's contribution flips from mildly positive to firmly cautious.
The twist: the bug barely mattered that day. We ran the counterfactual. Had the engine seen the crash, it would have trimmed exposure by less than a percentage point — and since our defensive book actually gained while the S&P fell that Monday, the "correct" signal would have changed almost nothing. One more twist: the U.S. market rebounded the very next day, so a panic-scaled reaction would have been the real mistake. We fixed the bug because wrong inputs are wrong, not because the outcome demanded it.
What we keep. Three habits came out of that Monday, now permanent: a daily log that scores whether the Asia signal actually predicted the U.S. session (two misses in its first two days — that's why we log instead of assume); a casebook where days like this are written down for the next engine revision; and the addendum practice itself — when reality outruns the seal, we say so on the page, same day.
Systems that never publish their bugs want you to believe they don't have any. Ours does, and you get to watch us fix them.
Educational content only. Not investment advice. All figures are from our published, timestamped records.