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

[mmcky]

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. Fix spelling and grammar in lecture text #1 and Fix intro overview: drop dangling Extensions item and renumber #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.

[Smit-create]

Since this is a static repo with very few updates on the lectures, we can skip having Netlify deployments on each PR. I have removed them from the workflows file.