web-release — production serves the build you tested, and the previous one is one command away

A frontend release fails quietly: the command exits 0, the CDN keeps the old bundle, a _headers file is ignored, or the build picked up an uncommitted file. The rule is the same as for any artifact: build once, test that build, promote that build.

1. Build from what CI checked

• git status --porcelain empty and HEAD = the commit whose CI is green (all checks, browser E2E included). The bundler packs the directory, not HEAD: another session's uncommitted edit would ship.
• Inject the commit into the bundle so it can be read back: NEXT_PUBLIC_BUILD_SHA, VITE_BUILD_SHA, or a generated public/version.json { "sha": "<40 hex>", "builtAt": … }.
• Use the lockfile (npm ci, pnpm i --frozen-lockfile), never a fresh resolve.

2. Preview first, always

Then e2e-test-engineer runs the Playwright golden paths against that preview URL. A local next start or a rebuild is a different artifact and is not evidence.

3. Promote — after gate:release

Promotion makes the tested deployment the production one. It does not rebuild.

• Never vercel --prod from a working tree as "the promote": that is a new build nobody tested.
• Gradual rollout where the host supports it (Vercel rolling releases, Workers percentage deploy): start small, decide on a named signal (error rate, Web Vitals for this deployment), then 100 %.
• The production domain and its DNS are infra-provisioner's. Missing domain → stop, route there.

4. Prove it landed

• The production URL's /version.json (or the build-sha meta tag) returns the promoted sha. Read it from outside the CDN edge cache — a cache-busting query — and read the age / cf-cache-status / x-vercel-cache response header.
• HTML is served fresh (cache-control: no-cache or short max-age); hashed assets are immutable. A long max-age on index.html keeps users on the old build for its full life.
• Purge only what changed (tags / paths), not the whole zone, and only when the host does not version automatically.
• Core journeys on production (Playwright smoke, logged in where the product needs it).
• Source maps: uploaded to the error tracker for this sha, not served publicly unless the project chose that.

5. Keep one rollback, clean the rest

Hosts keep deployments; your machine keeps dist/, .next/, .vercel/output, out/. After the release: keep the live deployment and the previous one; delete local build output of older releases by exact path (artifact-retention).

Report

WEB-RELEASE <project> @ <sha>
  ci       : PASS — all checks green on <sha> (run <id>)
  preview  : PASS — <deployment url / id>
  e2e      : PASS — playwright 9/9 on the preview URL
  promote  : PASS — after gate:release (<gate id>)
  landed   : PASS — /version.json = <sha>, cache MISS→HIT
  rollback : vercel promote <previous deployment url>