feat: use --id flag with branch name for stable preview URLs (#4357)

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: kenny <kenny@buildwithfern.com>

Author: devin-ai-integration[bot]

.github/workflows/preview-docs.yml

@@ -30,8 +30,9 @@ jobs:
         id: generate-docs
         env:
           FERN_TOKEN: ${{ secrets.FERN_TOKEN }}
+          HEAD_REF: ${{ github.head_ref }}
         run: |
-          OUTPUT=$(fern generate --docs --preview --instance fern-api.docs.buildwithfern.com/learn 2>&1) || true
+          OUTPUT=$(fern generate --docs --preview --id "$HEAD_REF" --instance fern-api.docs.buildwithfern.com/learn 2>&1) || true
           echo "$OUTPUT"
           URL=$(echo "$OUTPUT" | grep -oP 'Published docs to \K.*(?= \()')
           echo "preview_url=$URL" >> $GITHUB_OUTPUT

fern/fern.config.json

@@ -1,4 +1,4 @@
 {
   "organization": "fern",
-  "version": "4.29.0"
+  "version": "4.35.0"
 }