ci: Monitor client bundle size (#16327)

.github/workflows/ci-pull-requests.yml

@@ -12,11 +12,26 @@ jobs:
     runs-on: blacksmith-2vcpu-ubuntu-2204
     env:
       NODE_OPTIONS: '--max-old-space-size=4096'
+    outputs:
+      frontend_changed: ${{ steps.paths-filter.outputs.frontend == 'true' }}
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
         with:
           ref: refs/pull/${{ github.event.pull_request.number }}/merge
 
+      - name: Check for frontend changes
+        uses: dorny/paths-filter@v3
+        id: paths-filter
+        with:
+          filters: |
+            frontend:
+              - packages/frontend/**
+              - packages/@n8n/design-system/**
+              - packages/@n8n/chat/**
+              - packages/@n8n/codemirror-lang/**
+              - .bundlemonrc.json
+              - .github/workflows/ci-pull-requests.yml
+
       - name: Setup Environment and Build Project
         uses: ./.github/actions/setup-and-build
         with:
@@ -29,6 +44,45 @@ jobs:
       - name: Run typecheck
         run: pnpm typecheck
 
+      - name: Upload Frontend Build Artifacts
+        if: steps.paths-filter.outputs.frontend == 'true'
+        uses: actions/upload-artifact@v4
+        with:
+          name: editor-ui-dist
+          path: packages/frontend/editor-ui/dist/
+          retention-days: 1
+
+  bundle-size-check:
+    name: Bundle Size Check
+    needs: install-and-build
+    if: needs.install-and-build.outputs.frontend_changed == 'true'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+        with:
+          ref: refs/pull/${{ github.event.pull_request.number }}/merge
+
+      - name: Setup pnpm CLI
+        uses: pnpm/action-setup@a7487c7e89a18df4991f7f222e4898a00d66ddda # v4.1.0
+
+      - name: Setup Node.js
+        uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
+        with:
+          node-version: '22.x'
+          cache: pnpm
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Download Frontend Build Artifacts
+        uses: actions/download-artifact@v4
+        with:
+          name: editor-ui-dist
+          path: packages/frontend/editor-ui/dist/
+
+      - name: BundleMon
+        uses: lironer/bundlemon-action@v1.2.0
+
   unit-test:
     name: Unit tests
     uses: ./.github/workflows/units-tests-reusable.yml