`Shipment.shippedAt` Can Be Null, And ECHO Falls Back To The Recording Date

Shipment.shippedAt now returns the actual shipping date and may be null. V2 shipment creation no longer substitutes the create timestamp when a shipping date is missing, and the Amazon FBA importer no longer estimates a date from ship-by deadlines or the Orders API LastUpdateDate. Amazon dates that precede order creation are rejected outright. A caller that assumed shippedAt was always present should treat null as “shipping date unknown.”

An update that omits the shipping date or sends null preserves the existing date. Existing shipment dates are not changed automatically.

ECHO shipment reporting uses shippedAt when set, and the recording date when it is null, applied consistently to aggregation windows, daily buckets, and backfills. Clearing or adding a shipping date rebuilds both affected days without double-counting.