## High-Level Design / Dependencies

- **Architecture / system design overview**:
  - Responsive web app (PWA) — mobile-first capture + full-featured desktop review.
  - Backend API handling photo processing, pricing engine, and eBay integration.
  - **Core design principle**: Maximize deterministic systems. As much functionality as possible (pricing lookups, shipping recommendations, template application, duplicate detection, inventory reconciliation, eBay API interactions) must be rule-based and deterministic. AI is deliberately constrained to narrow, well-scoped tasks only (primarily vision-based identification and photo quality assessment) to minimize hallucinations and incorrect outputs.

- **External services, data sources, APIs**:
  - eBay OAuth + Sell APIs (Inventory, Fulfillment) for direct publishing and listing reconciliation.
  - eBay Browse API for sold and active listing data.
  - Vision models (GPT-4o / Claude 3.5 / Gemini) used only for identification and photo quality assessment, with strict "do not guess" rules.
  - Pricing data sources (eBay sold data primary; Keepa/Google Shopping as fallback).

- **Key technical dependencies**:
  - Secure per-user token storage and refresh handling.
  - Job queue for background processing of bulk uploads.
  - Structured templates and rules engine to constrain AI output.