Inventory Needs Sub-Minute Freshness for One Metric — Without Going Full Streaming

The case study's inventory dashboard currently refreshes hourly via a narrow inventory_refresh_hourly DAG. Ops now wants one specific metric — "SKUs currently out of stock" — updated within about a minute of the underlying stock level hitting zero, to trigger an automated reorder alert. Leadership does not want to re-architect the whole platform into a streaming system for this one metric.

1. Explain why simply shortening the existing hourly DAG's schedule to run every minute is the wrong fix, even though it looks like the obvious change.
2. Design a narrow path that meets the sub-minute requirement for just this metric, reusing as much of the existing architecture as makes sense.
3. What does this metric now need in terms of data-quality and alerting that the hourly version didn't, given the tighter action loop it feeds?