Duplicate a contiguous block of rows, N copies at a time

Cluster: tables

Scenario

A caller wants to duplicate not a single row but a contiguous run of rows as a group, say copying a 5-row template block and pasting it 10 times to build a repeating layout, in one operation rather than looping a single-row duplicate. Today the duplication affordance handles one row, with a repeat count for that one row; there is no first-class way to copy a multi-row block as a unit and stamp it several times at a chosen destination.

Spec note, not a corpus case: this is a feature-proposal generalization of an existing single-row operation, not a bug with a reproduction. The durable value is the operation's shape and the semantics it must preserve. When implemented it composes the existing row-op vocabulary and becomes assertable by reading back the pasted range's values, formulas, styles and heights.

Desired behavior

• A block-duplicate operation copies a contiguous run of rows as a group. Parameters (names illustrative): the first source row of the block, the block length (number of rows in the group), the destination row where the first copy is pasted, and the number of copies to generate. Copies are pasted contiguously in sequence starting at the destination.
• Single-row duplication remains a special case (length 1, one copy) and behaves exactly as the existing single-row duplicate does, so the block form generalizes it without breaking it.
• Each copy is faithful. Cell values, formulas, number formats, fonts, fills, borders, row heights, and outline levels of the source block are reproduced in every copy. Merged regions wholly inside the block are re-created per copy, and the merge and ref bookkeeping stays consistent, the same discipline the row-insert and duplicate cases already exercise for merges and table and image refs.
• Formula adjustment follows the existing rule. Relative references in copied formulas shift by the paste offset per copy, matching the single-row duplicate's relative-reference behavior; absolute references stay fixed. See duplicate-row-formula-relative-adjust.
• Interaction with structured content is defined. Duplicating a block that overlaps or extends a table, or that shifts anchored images or defined names below it, must keep the package valid and the refs consistent, or reject with a clear error if the operation would corrupt a table.

Open questions

• Insert-and-shift or overwrite: does pasting copies push existing rows down (insert semantics) or overwrite the destination rows? Insert semantics matches "duplicate rows" intent; make it explicit.
• Paste location relative to the source: is pasting a block onto a destination that overlaps the source range allowed, and if so what are the semantics?
• Does the copy include row-level data validations, conditional formatting ranges, and comments anchored in the block, or only cell content and style?

Related: duplicate-row-formula-relative-adjust, row-insert-and-duplicate-shift-merged-cells, duplicate-row-copies-faithfully-and-permits-merge, streaming-writer-worksheet-splice-rows-columns.