Version migration

The current contract is 2026-09-17, selected with Parcel-Version: 2026-09-17 and /v2 paths. The previous 2025-02-01 contract uses /v1 paths and the same header name with its older date. Do not mix an old version date with a v2 path: mismatches return HTTP 400 version_path_mismatch.

In v2, shipment creation sends package.weight_g and the list response contains shipments and next_cursor. In v1, creation sends mass_grams and list responses contain data and has_more. V1 uses offset pagination and has no opaque cursor. These are incompatible wire formats, not interchangeable aliases.

A question explicitly requesting v1 must use Legacy v1, even though the portal defaults to current documentation. An unspecified version should use v2 and state the version used. This corpus does not state a v1 sunset date; do not invent one.