diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml
new file mode 100644
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--- /dev/null
+++ b/.github/workflows/validate.yml
@@ -0,0 +1,45 @@
+name: Validate
+
+# The hermetic half of `.claude/csw.json` validate: lint and typecheck.
+# `pnpm build` is deliberately left out — it fetches the OpenAPI spec from the
+# live preview API, so gating PRs on it would make them depend on preview being up.
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+concurrency:
+  group: validate-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  lint-typecheck:
+    name: lint + typecheck
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          version: 10
+
+      - name: Set up Node
+        uses: actions/setup-node@v4
+        with:
+          node-version-file: .nvmrc
+          cache: pnpm
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Lint
+        run: pnpm lint
+
+      - name: Typecheck
+        run: pnpm typecheck