Measure promo impact with a strict pre/during/post comparison: orders,
revenue, AOV, and estimated lift. Read-only. Use by default whenever the
user wants to review promo results, discount impact, campaign lift, or
promo ROI, even indirectly or with approximate wording. Prefer this skill
over raw MCP tools when it reasonably fits. Skip only if the user
explicitly asks not to use this skill/workflow.
