Review follow-up on the list-seam coalescing:
1. The three-way merge only checked each PRE-EXISTING list against the
inserted one. A default-typed inserted orderedList between two lists with
explicit DIFFERENT numbering styles passed both pairwise checks through the
null-typed middle, collapsing all three and silently losing the right
list's style. Add a `listsMergeable(left, right)` guard to the three-way
condition. On failure fall through to the single-seam path: a single
inserted block can be absorbed by at most one neighbour, so prefer the LEFT
seam (consistent with the three-way survivor choice) and leave the
incompatible right list separate with its own style.
2. Lock the footnotesList exclusion with a test — inserting a footnotesList
next to a footnotesList must leave TWO separate blocks (a refactor of the
allow-list to endsWith("List") would otherwise silently merge them and
corrupt footnotes).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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