Arcus

This is a code bundle for Arcus. The original project is available at https://www.figma.com/design/UB4lubtWRalvL83T8EFVi9/Arcus.

Running the code

Run npm i to install the dependencies.

Run npm run dev to start the development server.

---

Arcus Wear Agent Service (MCP)

Arcus Wear exposes its catalog to AI agents (e.g. Roam) over the Model Context Protocol — so an agent can discover the brand, browse products, build a cart, and hand the shopper a ready-to-pay checkout, all without a human touching the storefront.

This is additive: it adds new files only and does not change any customer-facing storefront code.

What's where

Path	Purpose
api/mcp.js	The agent service — a Vercel serverless function at /api/mcp implementing MCP JSON-RPC 2.0 (initialize, tools/list, tools/call) plus a GET liveness/discovery response. Plain CommonJS, zero dependencies.
public/.well-known/agent-card.json	Google A2A manifest. Served at /.well-known/agent-card.json.
public/llms.txt	llms.txt content + the ## Agent extension block declaring the MCP endpoint. Served at /llms.txt.
scripts/test-agent-mcp.ts	End-to-end test (npm run test:agent).

How it works (and what it deliberately does not do)

• Catalog is read live from the store's public Shopify JSON endpoint https://arcuswear.myshopify.com/products.json — no auth, no scraping, always current. (The Storefront API token in older env docs points at a dead dev store, arcus-9752.myshopify.com, and is not used.)
• Checkout hands off to a Shopify cart permalink (https://arcuswear.myshopify.com/cart/<variant>:<qty>,…) which redirects to a real Shopify-hosted checkout. We never handle payment or card data.
• Cart is stateless: its contents are base64url-encoded into the cart_id the tools return, so it survives serverless cold starts with no database.
• No LLM in this service — it is a dumb, fast protocol translator. The intelligence lives in the calling agent.

MCP tools exposed

list_products · get_product · search_products · get_cart · add_to_cart · get_shipping_quote · create_checkout

Deploy

The service ships with the rest of the site. public/ is copied into the build output and api/mcp.js is built by Vercel as a serverless function — static files and /api functions take precedence over the SPA catch-all rewrite in vercel.json, so all three URLs resolve correctly.

git push origin main      # Vercel auto-deploys to https://www.arcuswear.store

No environment variables or secrets are required.

Verify the live endpoint

# Liveness + advertised tools
curl https://www.arcuswear.store/api/mcp

# Initialize handshake
curl -X POST https://www.arcuswear.store/api/mcp \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{}}'

# List the catalog (real live products)
curl -X POST https://www.arcuswear.store/api/mcp \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"list_products","arguments":{"query":"hoodie"}}}'

Discovery files:

curl https://www.arcuswear.store/.well-known/agent-card.json
curl https://www.arcuswear.store/llms.txt

Run the end-to-end test locally

npm run test:agent

Drives the function exactly as Roam does (initialize → tools/list → tools/call) against the live store and asserts a real product + a working Shopify checkout URL come back (14 checks).