Compatible list containers should share wrapper-unit transplant semantics not just local insert semantics

What happened

After widening the wrapper-unit seam so ordered-list could use the same list-item contract as bulleted-list, the next useful question was:

• does that only help local ordered-list inserts?
• or can an ordered-list fragment transplant into a bulleted-list target through the same seam?

What fixed it

The same seam should handle both.

Once the list container types are compatible, the fragment should be allowed to contribute its list-item children to the target wrapper-list seam even when the source and target container flavors differ.

Why this works

The important contract is not the source container label.

It is:

• compatible wrapper-list container
• same sibling unit type
• same post-insert selection/range semantics

If those hold, transplant should share the seam.

Reusable rule

When widening wrapper-unit support from one list container flavor to another:

• do not stop at “same-flavor inserts are green”
• also prove cross-container transplant between the compatible flavors

Related issues

• 2026-04-05-wrapper-unit-insert-seams-should-generalize-from-bulleted-list-to-compatible-list-containers-before-adding-new-geometry.md