Selected Paragraph Undo

Restore specific paragraphs in-place to a client-provided snapshot.

Used by the reader's "Undo" affordance after selected-paragraph apply: the client snapshots the pre-apply paragraphs before applying, then if the user dislikes the result it sends them back here. Pure DB write - no LLM, no decompose. Costs 0 credits.

When the lengths match, restored_paragraphs is parallel to paragraph_indices; entry i replaces the chapter's paragraph at index paragraph_indices[i]. When the lengths differ, paragraph_indices must be one contiguous current range, and that whole range is spliced out and replaced with restored_paragraphs. This lets undo collapse a 1->3 expansion back to the original single paragraph without duplicating the following prose.

Map restore uses only trusted server ledger/event snapshots correlated by range/operation_id. Clients never supply an authoritative map snapshot.

Fallback for tools whose payload is still being tightened.