Add OpenAPI spec drift check to CI

Runs the test suite with OPENAPI=1 and fails if docs/openapi.yml has
uncommitted changes, ensuring the checked-in spec stays in sync with
the actual API responses.

https://claude.ai/code/session_01F4qY2LA6JYqsvdLi4xkLVA

Author: tvdeyen

.github/workflows/ci.yml

@@ -45,6 +45,40 @@ jobs:
           DB_USER: user
           DB_PASSWORD: password
         run: bundle exec rake
+  OpenAPI:
+    runs-on: ubuntu-22.04
+    env:
+      ALCHEMY_BRANCH: main
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: "3.4"
+          bundler-cache: true
+      - name: Restore apt cache
+        id: apt-cache
+        uses: actions/cache@v4
+        with:
+          path: /home/runner/apt/cache
+          key: apt-sqlite-
+      - name: Install SQLite headers
+        run: |
+          sudo mkdir -p /home/runner/apt/cache
+          sudo apt-get update -qq
+          sudo apt-get install -qq --fix-missing libsqlite3-dev -o dir::cache::archives="/home/runner/apt/cache"
+          sudo chown -R runner /home/runner/apt/cache
+      - name: Regenerate OpenAPI spec
+        env:
+          RAILS_ENV: test
+          OPENAPI: "1"
+        run: bundle exec rake
+      - name: Check for OpenAPI spec drift
+        run: |
+          if ! git diff --exit-code docs/openapi.yml; then
+            echo "::error::docs/openapi.yml is out of date. Run 'OPENAPI=1 bundle exec rspec' locally and commit the result."
+            exit 1
+          fi
   Vitest:
     runs-on: ubuntu-24.04
     env: