Add info comment to preview build

.github/workflows/preview-build.yml

@@ -53,6 +53,11 @@ on:
         type: boolean
         default: false
         required: false
+      enable-cumulative-comment:
+        description: 'Enable info comment'
+        type: boolean
+        default: false
+        required: false
 
 permissions:
   contents: read
@@ -371,6 +376,7 @@ jobs:
           ALL_CHANGED_FILES: ${{ needs.check.outputs.all_changed_files }}
           PATH_PREFIX: ${{ needs.build.outputs.path_prefix }}
         with:
+          # language=javascript
           script: |
             const title = '## 🔍 Preview links for changed docs'
             const changedMdFiles = process.env.ALL_CHANGED_FILES
@@ -438,3 +444,58 @@ jobs:
                 body:body.join('\n'),
               });
             }
+      - name: Comment on docs changes about versioning requirements
+        if: inputs.enable-cumulative-comment == 'true'
+        uses: actions/github-script@v7
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          # language=javascript
+          script: |
+            const pr = context.payload.pull_request;
+            const prNum = pr.number;
+            const owner = context.repo.owner;
+            const repo = context.repo.repo;
+
+
+            const { data: comments } = await github.rest.issues.listComments({
+              owner, repo, issue_number: prNum
+            });
+
+            const title = '## ℹ️ Important: Docs version tagging';
+
+            const existingComment = comments.find(c =>
+              c.user.type === 'Bot' &&
+              c.body.startsWith(title)
+            );
+
+            if (existingComment) return;
+
+            const body = `${title}
+
+            👋 Thanks for updating the docs! Just a friendly reminder that our docs are now **cumulative**. This means all 9.x versions are documented on the same page and published off of the main branch, instead of creating separate pages for each minor version.
+
+            We use [applies_to tags](https://elastic.github.io/docs-builder/syntax/applies) to mark version-specific features and changes.
+
+            <details>
+            <summary>Expand for a quick overview</summary>
+
+            ### When to use applies_to tags:
+            ✅ At the page level to indicate which products/deployments the content applies to (mandatory)
+            ✅ When features change state (e.g. preview, ga) in a specific version
+            ✅ When availability differs across deployments and environments
+
+            ### What NOT to do:
+            ❌ Don't remove or replace information that applies to an older version
+            ❌ Don't add new information that applies to a specific version without an applies_to tag
+            ❌ Don't forget that applies_to tags can be used at the page, section, and inline level
+            </details>
+
+            ### 🤔 Need help?
+            - Check out the [cumulative docs guidelines](https://elastic.github.io/docs-builder/contribute/cumulative-docs/)
+            - Reach out in the [#docs](https://elastic.slack.com/archives/C0JF80CJZ) Slack channel`;
+
+            await github.rest.issues.createComment({
+              owner, repo,
+              issue_number: prNum,
+              body
+            });