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core/sellers/services against docs/backend/PHASE-5-SELLER-PORTAL- CONTRACT.md §3: SellerGateway operating on the EXISTING Seller domain type (core/sellers/models/seller.model.ts - deliberately not a new competing shape; GAPS-AND-IMPROVEMENTS.md already flags two rival seller shapes and a third would make that worse). Adds SellerUser/SellerRole. Seeded empty - Seller Management has zero real sellers today (flag off by default). Scope note: this session's largest deferral. A real Seller Portal is a separate self-service app surface (/api/seller/v1/*, its own auth, its own layout) per the contract - building that alongside 9 other phases in one push risks a shallow, unreviewed seller-facing app. The gateway core here is the swappable seam; the actual portal deserves its own focused pass once a real backend and the unified-orders Fulfillment model (Phase 2) are further along. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>