CI fails on Netlify preview deploy: NETLIFY_AUTH_TOKEN / NETLIFY_SITE_ID not set

Summary

The Build Project [using jupyter-book] workflow (ci.yml) fails on every PR — but not because of the build. The jupyter-book build succeeds; the job dies on its final step, Preview Deploy to Netlify, because the required secrets are not configured in this repo.

Evidence

From the failed run on PR #1 (run 26938631605), step conclusions:

success   Build Download Notebooks (sphinx-tojupyter)
success   Build HTML
success   Install Node.js
failure   Preview Deploy to Netlify   <-- only failure

Error message:

Error: Authentication required. NETLIFY_AUTH_TOKEN is not set and
`netlify login --request <message>` can be used to authenticate.
##[error]Process completed with exit code 1.

gh secret list for the repo returns nothing — no Actions secrets are configured. The step at .github/workflows/ci.yml (Preview Deploy to Netlify) passes secrets.NETLIFY_AUTH_TOKEN and secrets.NETLIFY_SITE_ID, which are empty, so the Netlify CLI exits 1 and the whole job goes red.

Impact

• Pre-existing and repo-wide — affects every PR (e.g. #1 and #3), unrelated to the content of any individual PR. The lectures themselves build cleanly.
• Because the job goes red, the build result is masked by an infrastructure step, which makes it hard to tell at a glance whether a real build break has occurred.

(There is also a separate older failure on main in the Build & Publish to GH Pages workflow — likely the same class of missing-config/secret issue — worth a look while we're here, but tracked separately if needed.)

Options to resolve

1. Add the secrets (enables PR previews) — a repo/org admin sets NETLIFY_AUTH_TOKEN and NETLIFY_SITE_ID under Settings → Secrets and variables → Actions. The QuantEcon org already uses Netlify previews on the other lecture repos, so a token should exist.
2. Guard the step so CI is green when the token is absent (e.g. forks / before secrets land):

   - name: Preview Deploy to Netlify
     if: ${{ env.NETLIFY_AUTH_TOKEN != '' }}
     env:
       NETLIFY_AUTH_TOKEN: ${{ secrets.NETLIFY_AUTH_TOKEN }}
     # ...
   

   (Secrets can't be referenced directly in if:, so map to env first, then test env.)
3. Remove the Netlify preview step if previews aren't wanted for this repo.

Recommended: option 1 if we want previews here, with option 2 as a resilience improvement regardless so the build remains the real pass/fail signal.

Start with .github/workflows/ci.yml lines 79-85 and the failed run linked in the issue. Confirm how the Preview Deploy to Netlify step receives its secrets and how the preceding build steps report success. Done means the workflow’s intended preview or missing-secret behavior is explicit, while the Jupyter Book build remains the meaningful CI result.