Increment design (phase #2 of the approved 2026-05-27 centralized-billing spec) to make Odoo fusion_centralize_billing the system of record for NexaCloud billing: build -> import -> dual-run -> gated flip, NexaCloud first, one subscription per deployment, go-forward billing only. Plan 01 = the Odoo subscription-cancel endpoint (test-first). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>