DEV: Introduce Zeitwerk reloading check in CI (#22151)

This should help us to catch the most catastrophic cases where plugins fail to auto-reload in development mode.

.github/workflows/tests.yml

@@ -156,7 +156,7 @@ jobs:
           key: rspec-runtime-${{ matrix.build_type }}-${{ matrix.target }}-${{ github.run_id }}
           restore-keys: rspec-runtime-${{ matrix.build_type }}-${{ matrix.target }}-
 
-      - name: Run Zeitwerk check
+      - name: Check Zeitwerk eager_load
         if: matrix.build_type == 'backend'
         env:
           LOAD_PLUGINS: ${{ (matrix.target == 'plugins') && '1' || '0' }}
@@ -172,6 +172,21 @@ jobs:
             exit 1
           fi
 
+      - name: Check Zeitwerk reloading
+        if: matrix.build_type == 'backend'
+        env:
+          LOAD_PLUGINS: ${{ (matrix.target == 'plugins') && '1' || '0' }}
+        run: |
+          if ! bin/rails runner 'Rails.application.reloader.reload!'; then
+            echo
+            echo "---------------------------------------------"
+            echo
+            echo "::error::Zeitwerk reload failed - the app will not be able to reload properly in development."
+            echo "To reproduce locally, run \`bin/rails runner 'Rails.application.reloader.reload!'\`."
+            echo
+            exit 1
+          fi
+
       - name: Core RSpec
         if: matrix.build_type == 'backend' && matrix.target == 'core'
         run: bin/turbo_rspec --use-runtime-info --verbose