Backfills & Idempotency — Week 2 CheckThe rerun-safety stack: the idempotency contract, safe reloads, incremental state, and blast radius. Every question is answerable from the Week 2 brief.

A backfill of last March produces different numbers than March's original runs did. The most likely contract violation?

Why is delete-then-insert unsafe for a retried task, and what replaces it?

A DB query sits at the top level of a DAG file, outside any task. What actually happens?

Per the incremental-state boundary rule, which pipeline is the RIGHT candidate for incremental processing?

What single property gates whether lineage-driven automated backfill (walk the graph, re-run every downstream) is safe?

In a blue-green reload, what makes the cutover 'atomic' from the consumers' perspective?