Deploying to Vercel#

Every build regenerates the complete Build Output API v3 layout — the route table, the static tier and the bundled render function. This guide walks the layout, the two runtimes, and why the entry's { fetch } shape is load-bearing.

The generated layout#

.vercel/output/
├── config.json                # routes: fn prefix → filesystem → catch-all
├── static/                    # the client outDir (minus index.html, .vite)
└── functions/_render.func/    # the bundled server + .vc-config.json

The Build Output API is a generation contract — hand-writing it has no copyability value, so generate() rebuilds it every time. Two layout choices are load-bearing:

• static/ omits index.html — the filesystem handle would serve static/index.html for /, shadowing the document render with the raw outlet template.
• The server-fn route precedes the filesystem handle — POSTs to /_sigx/fn/* must never be shadowed by files.

The platform entry — yours, scaffolded once#

The first build scaffolds src/entry.vercel.ts iff absent and never touches it again. The composition order stays visible in your file:

static assets  →  server functions  →  document render

The export default { fetch } shape is load-bearing on the Node runtime: Vercel's launcher detects a web handler by the fetch method on the default export — a bare default function would be treated as a legacy (req, res) handler.

Node vs Edge#

The default runtime is node — Vercel's current guidance (Fluid compute). Edge is opt-in:

vercel({ runtime: 'edge' })

For runtime: 'edge' the build resolves the edge-light/worker conditions and generate() emits a tiny wrapper entrypoint — the edge contract is a bare default fetch function, while your entry keeps the { fetch } shape, identical across platforms.

Deploy#

vite build --app -c vite.config.vercel.ts
vercel deploy --prebuilt          # add --prod for production

Verification posture#

Structural, not emulation (there is no official Build Output API emulator): CI asserts the generated layout and invokes the function's fetch export directly under Node with real Requests — exactly what Vercel's launcher calls. The reference wiring lives at examples/resume in the SignalX core repo (vite.config.vercel.ts + the committed src/entry.vercel.ts).