TCLOUD-4780 Support atomic updates

Author: tiny-james

.github/workflows/preview_create.yml

@@ -59,7 +59,12 @@ jobs:
 
     - name: Upload website preview to S3 # put in the docs subfolder as we rely on that path in redirects
       run: |
-        aws s3 sync --delete ./build s3://tiny-cloud-antora-docs-preview/pr${PR_NUMBER}
+        aws s3 sync ./build s3://tiny-cloud-antora-docs-preview/pr${PR_NUMBER}/${GITHUB_RUN_ATTEMPT}
 
     - name: Create redirects on S3
-      run: node ./.github/workflows/scripts/generate_redirects.mjs tiny-cloud-antora-docs-preview pr${PR_NUMBER}
+      run: |
+        node .github/workflows/scripts/generate_redirects.mjs tiny-cloud-antora-docs-preview pr${PR_NUMBER}/${GITHUB_RUN_ATTEMPT}
+
+    - name: Update pointer to current run output # put in the docs subfolder as we rely on that path in redirects
+      run: |
+        aws s3api put-object --bucket tiny-cloud-antora-docs-preview --key pr${PR_NUMBER}/index.html --body .github/workflows/scripts/empty.html --content-type text/html --metadata pointer=${GITHUB_RUN_ATTEMPT}

.github/workflows/scripts/generate_redirects.mjs

@@ -339,7 +339,7 @@ const main = async () => {
     return Promise.reject(`Invalid bucket name, got ${bucket}`);
   }
 
-  if (!/^[a-z0-9\.-]+$/.test(prefix)) {
+  if (!/^[a-z0-9\.-]+(\/[a-z0-9\.-]+)*$/.test(prefix)) {
     return Promise.reject(`Invalid prefix, got ${prefix}`);
   }