Cold-chain overnight shipping, how do you wire FedEx Priority Overnight + UPS Next Day Air into Magento?

Cold-chain is the single biggest operational risk in gourmet ecom, a 24-hour delay turns $200 of caviar into a refund + a one-star review. The stack I ship:

• FedEx Priority Overnight and UPS Next Day Air as primary carriers, both wired via official Magento connectors (FedEx Web Services, UPS API). Rates pull live at cart based on origin warehouse, destination ZIP, weight, and dim weight (gel-pack-padded boxes are dim-heavy).
• Day-of-week cutoff logic, orders placed after 2pm Thursday or any time Friday, Sunday auto-ship Monday to avoid weekend-warehouse spoilage. Built as a Magento sales-rule + shipping-method observer with per-product overrides for ambient-shippable items.
• Per-SKU shipping flags, each product has requires_cold_chain, max_transit_days, and gel_pack_count attributes. Cart aggregates the most restrictive value across line items and offers only carriers/services that meet it.
• ZIP-code transit overlay, FedEx and UPS publish service-area maps; some rural ZIPs that nominally support overnight actually need 2-day. A nightly cron pulls the latest service-area file and flags risky ZIPs at checkout with a warning banner.

Hardest piece is the weather-hold rule: when destination forecast is above 90°F or there’s a winter-storm advisory at origin, the checkout offers a one-click reschedule rather than shipping into a guaranteed melt. I’ve seen this cut spoilage refunds by 60-80% during heatwaves.