Multiple complex list units still reduce to one wrapper-list fragment when each unit is already proved

What happened

After proving one list-item unit with:

• paragraph
• nested list
• quote

the next step was selection across multiple sibling units with that same complex shape.

What fixed it

It did not need a new seam.

The fragment simply lifts one level:

• each complex list-item remains one proved wrapper unit
• selection across sibling units becomes one bulleted-list fragment of those sibling units
• DOM and Chromium round-trip that wrapper-list fragment cleanly

Why this works

The wrapper-unit boundary is still doing the real work.

If each sibling unit is already a proved unit shape, then selecting across multiple siblings does not automatically create a new transform problem.

The fragment is just:

• one proved wrapper list
• containing already-proved wrapper units

Reusable rule

When widening from one proved wrapper unit to many sibling wrapper units:

• first ask whether the fragment simply becomes one wrapper list of those units
• if yes, prove the round-trip through DOM and browser before inventing a new transform abstraction

Related issues

• 2026-04-05-wrapper-units-can-expand-from-paragraph-plus-list-or-quote-to-paragraph-plus-list-plus-quote-without-a-new-insert-seam.md