fix(setup): simplify first-run output

Author: bhdicaire

custom/v8s-links.txt

@@ -12,8 +12,8 @@ predictable version numbers, changelog entries, and release notes so instance ow
 The code repository uses Conventional Commits for change intent. The repository also includes a GitHub Actions workflow
 at `.github/workflows/release-please.yml`.
 
-The code repository has `npm run lint`, implemented by `scripts/lint.mjs`, and `npm run check`, which runs build, lint,
-and tests. It does not currently use an automatic formatter such as Prettier or Biome.
+The code repository has `npm run lint`, implemented by `scripts/lint.mjs`, and `npm run check`, which runs formatting,
+build, lint, and tests.
 
 ## Decision
 
@@ -36,5 +36,4 @@ repositories should not publish vanityURLs product releases.
 - Product releases are repeatable and tied to commit intent
 - Instance owners can refer to release notes before upgrading
 - Conventional Commits matter for release automation, not just readability
-- Lint and test automation exist through npm scripts, but automatic formatting is intentionally not part of the current
-  toolchain
+- Formatting, lint, build, and test automation exist through npm scripts

custom/v8s-policies.json

@@ -0,0 +1,43 @@
+# 0011. Use Prettier and a single check gate
+
+Date: 2026-05-26
+
+Status: Accepted
+
+## Context
+
+vanityURLs includes JavaScript, JSON, Markdown, HTML, CSS, TOML, and YAML files. Before this decision, the repository
+had custom linting and tests, but no automatic formatter. Formatting drift could show up late, and CI could not enforce
+the same style that maintainers use locally.
+
+The project also needs one obvious command for local verification and CI/CD. Instance owners should not need to remember
+separate format, build, lint, and test commands before pushing.
+
+## Decision
+
+Use Prettier as the automatic formatter for supported text files.
+
+Expose two explicit formatting commands:
+
+- `npm run format` rewrites supported files with Prettier
+- `npm run format:check` verifies that supported files already match Prettier output
+
+Keep `scripts/lint.mjs` as the project-specific lint layer for checks Prettier does not cover, including trailing
+newlines, JSON parse errors, JavaScript syntax checks, and vanityURLs-specific `wrangler.toml` expectations.
+
+Make `npm run check` the single local and CI gate. It runs, in order:
+
+1. `npm run format:check`
+2. `node scripts/build.mjs`
+3. `npm run lint`
+4. `npm test`
+
+The GitHub Actions check workflow runs `npm ci` followed by `npm run check`.
+
+## Consequences
+
+- Formatting is deterministic locally and in CI
+- Maintainers can run `npm run format` before committing noisy style changes
+- `npm run check` remains the one command to run before pushing
+- Prettier does not replace project-specific linting or runtime tests
+- The installer can run the same check gate quietly and show a concise setup result