## Stack

- **Language:** ES modules (no build step, no transpile — source ships as-is).
- **Key deps:** `lit` ^3 (web components, the one runtime dep); `@playwright/test` (the one dev dep, visual regression).
- **Components:** shadow-DOM Lit elements that adopt a shared stylesheet so the Layer 1 `.wn-*` utility classes work inside the shadow root. `src/elements/_styles.js` is **auto-generated** from `src/styles/components.css` by `scripts/sync-shared-styles.mjs` — never hand-edit it.

## Dev Commands

```bash
pnpm install
pnpm showcase                 # serve :4321 → /examples/showcase/  (every component)
pnpm example                  # serve :4322 → examples/whynot-control
pnpm test:visual              # Playwright visual-regression run (auto-starts a static server)
pnpm test:visual:update       # regenerate screenshot baselines after an intentional change
pnpm check                    # check-changelog: fails if CHANGELOG.md gained no entry vs main
npx playwright test -g "inbox"  # run a single visual test by name

make                          # list make targets (help is the default goal)
make designbook-sync          # after a /design-sync pull, record changes + last-sync time → RecentChanges.md
make designbook-check         # ask Claude Design (via llm-connect) if the cloud is newer; warn if mirror is stale
make recent-changes           # regenerate RecentChanges.md (alias; ARGS="--range main..HEAD" supported)
make sync-styles              # = node scripts/sync-shared-styles.mjs
```

There is no unit-test suite — correctness is verified by full-page Playwright screenshot diffs of the two `examples/` pages (`tests/visual/ui-kit.spec.mjs`, `maxDiffPixelRatio: 0.005`). Any visual change needs `pnpm test:visual:update` + baseline review.

## Integrating the designbook

The **designbook** is the upstream atelier — the **Claude Design project** (cloud, `claude.ai/design`), source of truth for the *language*. Its local mirror lives in-repo at `designbook/` (see `designbook/README.md`). Sync is **agent-driven and incremental** (one component at a time, never a wholesale replace):

1. **Pull** — run `make designbook-pull` (`scripts/designbook_pull.py`). It drives the local `claude` binary headless (`claude --print --permission-mode acceptEdits`), which has the `DesignSync` tool over the claude.ai login, to fetch the React designbook and write it into `designbook/`; the file contents stay in that subprocess, so the pull is cheap regardless of size. Selection is governed by `designbook/.design-pull.json` (it excludes `_whynot-design-seed/**`, the cloud project's copy of this repo). The script stamps freshness itself on success. **Note:** the bundled `/design-sync` skill goes the *other* way — it *pushes* a repo up to Claude Design — so it does **not** populate `designbook/`; use `make designbook-pull` for the pull (see `designbook-propagation.md`).
2. **Record** — `make designbook-sync` runs `scripts/designbook-sync.mjs`, writing `RecentChanges.md`: a **snapshot** (not a log) of what changed across `designbook/` + the derived surfaces (`tokens/`, `src/styles/`, `src/elements/`, `examples/`), grouped by layer.

**Freshness** is tracked in `designbook/.design-sync.json` (`lastSyncAt`, `remoteUpdatedAt`, `projectId`, `projectName`). Every report states **"Last /design-sync: <datetime>"** so it's clear whether the snapshot reflects the latest design. The cloud-ahead check is backed by **llm-connect** (`make designbook-check` → `scripts/check_designbook_staleness.py`): it uses the `claude-code` adapter to ask the local `claude` binary for the project's current `updatedAt` via `DesignSync.list_projects`, then records it with `node scripts/designbook-sync.mjs --remote-updated <iso>`. Only the `claude-code` adapter can reach the user's Claude Design project (Gemini/OpenRouter/OpenAI cannot), and no secret goes in the prompt — DesignSync uses the claude.ai login (see `credential-routing.md`). The check needs `llm_connect` importable; the Makefile auto-selects `~/llm-connect/.venv/bin/python`. Use `--remote-updated <iso>` to run the comparison offline/manually, or `--fail-if-stale` (exit 3) in automation. When `remoteUpdatedAt` is newer than `lastSyncAt`, the report and stdout **warn that the local mirror is OUTDATED** until the next `/design-sync`. If no sync was ever recorded, it warns that `/design-sync` has not run. The reporter is deterministic (built from `git status`/`git diff`), only writes the working tree, never commits, and never edits `designbook/` content. Fold notable entries into `CHANGELOG.md` under `## [Unreleased]` before releasing — `RecentChanges.md` is overwritten every run and is **not** the CI-enforced artifact.