Fix: Remove duplicate separators in action menus

[daizutabi]

📝 Summary

This PR fixes an issue where duplicate separators could appear in the cell action dropdown and the cell context menu.

When action items within a group are filtered out (e.g., based on context), the group can become empty. The rendering logic did not account for this, causing separators to be rendered between these empty groups, resulting in visible duplicate separators. This was particularly noticeable in setup cells.

Closes #8492

🔍 Description of Changes

The solution is to filter the list of action groups before rendering. This change removes any groups that are empty after their items have been filtered. By ensuring we only iterate over visible, non-empty groups, we can guarantee that separators are only rendered between actual content.

For CellActionsDropdownInternal in frontend/src/components/editor/cell/cell-actions.tsx:

  const actions = useCellActionButtons({ cell: props, closePopover });

  const visibleActions = actions
    .map((group) => group.filter((action) => !action.redundant))
    .filter((group) => group.length > 0);

The similar approach was applied to CellActionsContextMenu in frontend/src/components/editor/cell/cell-context-menu.tsx.

AI-Assisted Investigation: An AI agent also performed a broad search for the keyword "Separator" across the frontend/src directory to identify any other components that might have a similar bug pattern. No other instances of this issue were found.

📋 Checklist

• I have read the contributor guidelines.
• For large changes, or changes that affect the public API: this change was discussed or approved through an issue, on Discord, or the community discussions (Please provide a link if applicable).
• Tests have been added for the changes made.
• Documentation has been updated where applicable, including docstrings for API changes.
• Pull request title is a good summary of the changes - it will be used in the release notes.

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Feb 27, 2026 10:35pm

[mscolnick]

clean fix, thank you!