- Keep `const partBodyHtml=_getCachedRender(partDisplayText,false);` line
intact (test_issue3397 asserts the exact source string), apply snapshot
stamping on the following line via partBodyHtmlStamped.
- Drop unused roots_before variable and unused import in
test_media_message_snapshots.py (ruff F841/F401 on new lines).
- Update the source-invariant assertion to the two-line stamp shape.