diff --git a/.github/workflows/build.yaml b/.github/workflows/build.yaml
new file mode 100644
index 0000000..9f6a6ba
--- /dev/null
+++ b/.github/workflows/build.yaml
@@ -0,0 +1,34 @@
+name: Build
+
+# Builds every PR, including the drafts the fil-one docs sync workflow opens
+# (see AGENTS.md). Holds no secrets: a PR's MDX runs during the build.
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+permissions:
+  contents: read
+
+concurrency:
+  group: build-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+
+      - uses: actions/setup-node@949feb2413d6458794dcd2491c4babbbce0c15c1 # v6
+        with:
+          node-version: 24
+          cache: npm
+
+      - run: npm ci --ignore-scripts --no-audit --no-fund
+
+      - run: npm run build
diff --git a/AGENTS.md b/AGENTS.md
index df89b6c..e91045d 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -41,3 +41,11 @@ npm run build
 ```
 
 This catches MDX syntax errors (broken JSX, unclosed tags, invalid frontmatter) that won't show up just from reading the file.
+
+## Drafts from the fil-one docs sync workflow
+
+Some PRs here are drafted by an AI agent in the `fil-one/fil-one` repo's **Docs sync** workflow (design: `docs/DocsSync.md` in that repo). They come from the branch `docs-sync/fil-one-<PR number>`, carry the `docs-sync` label, and link to the product PR they follow. The rules above apply to them like any other change; the agent is told to follow this file.
+
+- The agent may edit only `docs/**` and the two `static/llms*.txt` mirrors. Changes it needs elsewhere (`sidebars.js` for a new page, `docusaurus.config.js`, `vercel.json` redirects) are listed under "Manual follow-ups" in the PR body.
+- Claims under "Needs verification" are the ones the code alone could not settle (region behaviour, a flag's production state). Confirm them before approving.
+- The PR stays a draft until the product PR merges, and is regenerated on each push to the product PR. Push a commit to the branch to take it over: the workflow then stops regenerating it. Close the PR to stop it for good.