Sub-documents

Document	Topic
problem.md	The CORS problem — root cause analysis of why createServerFn inside a factory function doesn't work
architecture.md	Three-layer invoke architecture and comparison with deco-cx/deco
generator.md	The generate-invoke.ts script — how it works, how to run it, how to extend
troubleshooting.md	Common issues and how to debug them

Deco Server Functions & Invoke

How server-side actions (cart, checkout, newsletter, masterdata) are called from the browser in Deco TanStack Start storefronts.

The Problem in One Sentence

TanStack Start's createServerFn compiler only transforms .handler() calls at module top-level — wrapping it in a factory function (createInvokeFn) causes the compiler's "fast path" to skip it, sending raw VTEX API calls to the browser and causing CORS errors.

The Solution in One Sentence

A build-time generator (generate-invoke.ts) reads the action definitions from @decocms/apps and emits invoke.gen.ts with each createServerFn().handler() as a top-level const, which the compiler correctly transforms into RPC stubs.

Quick Reference

Client (useCart)
  → invoke.vtex.actions.addItemsToCart({ data: {...} })
  → createClientRpc("base64id")          ← compiler-generated stub
  → POST /_server                         ← same domain, no CORS
  → TanStack Start server handler
  → addItemsToCart(orderFormId, items)    ← pure function from @decocms/apps
  → vtexFetch → VTEX API                  ← server-to-server, has credentials
  → Response → client

Layer Responsibilities

Layer	Package	Role
Commerce functions	@decocms/apps	Pure async functions (addItemsToCart, subscribe, etc.) — no framework deps
Generator	@decocms/start	generate-invoke.ts script that creates top-level createServerFn declarations
Generated bridge	Site (invoke.gen.ts)	Auto-generated file with RPC-transformable server functions
Consumer	Site components	Import invoke from ~/server/invoke.gen

Setup for a New Site

# 1. Generate the invoke file
npx tsx node_modules/@decocms/start/scripts/generate-invoke.ts

# 2. Import in components
import { invoke } from "~/server/invoke.gen";
const cart = await invoke.vtex.actions.addItemsToCart({
  data: { orderFormId, orderItems }
});

Add to package.json:

{
  "scripts": {
    "generate:invoke": "tsx node_modules/@decocms/start/scripts/generate-invoke.ts",
    "build": "npm run generate:blocks && npm run generate:invoke && npm run generate:schema && tsr generate && vite build"
  }
}

Key Files

File	Location	Purpose
generate-invoke.ts	@decocms/start/scripts/	Build-time generator script
invoke.gen.ts	Site src/server/	Generated file with top-level server functions
vtex/invoke.ts	@decocms/apps/	Source of truth for action definitions (parsed by generator)
vtex/actions/*.ts	@decocms/apps/	Pure commerce functions

When to Re-generate

Re-run npm run generate:invoke when:

• Adding new actions to @decocms/apps/vtex/invoke.ts
• Changing action signatures (input types, return types)
• Updating @decocms/apps dependency