Railway ignores RAILPACK_NODE_VERSION and package.json engines field

Question

After pushing a change to my Svelte + Bun project today, Railway's build failed while the same build succeeds locally with Node 22.18.0.

**What happened:**
- Railway automatically installed Node 25.2.1 and the build failed
- Locally with Node 22.18.0: build succeeds
- Locally with Node 25.2.1: build fails (confirming it's a version issue)

**What I tried:**
1. Set `RAILPACK_NODE_VERSION=22.18.0` environment variable → build still failed
2. Added `"engines": { "node": "22.18.0" }` to package.json → build still failed
3. Added `mise.toml` file → build finally succeeded

**Expected behavior:**
Either the `RAILPACK_NODE_VERSION` environment variable or the `engines.node` field in package.json should have pinned the Node version to 22.18.0, but neither worked.

**Workaround:**
Using `mise.toml` works, but it seems like the other standard methods should have worked first.