From ec678ed495e8e0f20d96b6af3206521626013263 Mon Sep 17 00:00:00 2001
From: Steffen Becker <stffn.becker@gmail.com>
Date: Sun, 28 Jun 2026 10:30:00 +0200
Subject: [PATCH] feat: table cell splitting/merging

---
 CHANGELOG.md                               |   4 +-
 src/lib/components/Editor.svelte           |  29 ++-
 src/lib/components/TableSplitDialog.svelte | 152 ++++++++++++++
 src/lib/components/TableToolbar.svelte     |  42 +++-
 src/lib/editor/extensions.ts               |   3 +
 src/lib/editor/extensions/tableSplit.ts    | 230 +++++++++++++++++++++
 src/lib/export/odt.ts                      |  12 +-
 tests/roundtrip.test.ts                    |  44 +++-
 tests/unit/table-split.test.ts             |  95 +++++++++
 9 files changed, 603 insertions(+), 8 deletions(-)
 create mode 100644 src/lib/components/TableSplitDialog.svelte
 create mode 100644 src/lib/editor/extensions/tableSplit.ts
 create mode 100644 tests/unit/table-split.test.ts

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0de7b1a..100e208 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -33,7 +33,7 @@
 - Tab stops (real tab character) and manual line breaks (Shift+Enter)
 
 **Insert**
-- Tables: insert via size picker, Word-style row/column drag-resize, add / delete rows & columns, delete table, cell borders; a table splits cleanly across page boundaries
+- Tables: insert via size picker, Word-style row/column drag-resize, add / delete rows & columns, delete table, cell borders, merge cells and split cells (N×M, Word/LibreOffice-style); a table splits cleanly across page boundaries
 - Images: inline or floating with text wrap (left / right / top-bottom), resize handles, rotation, live size badge; insert via toolbar, drag-and-drop, or paste
 - Special characters picker
 - Hyperlinks: create / edit / remove (toolbar + Ctrl+K), Ctrl/Cmd+click to open, hover hint showing the URL; ODF `text:a` round-trip
@@ -65,7 +65,7 @@
 ### Not yet implemented
 
 Planned word-processor features (to match Word/LibreOffice):
-- Table cells: merge / split, cell background/shading, header-row toggle
+- Table cells: cell background/shading, header-row toggle
 - Footnotes / endnotes (currently dropped on import)
 - Clear formatting (remove all marks)
 - Multi-column (newspaper) layout
diff --git a/src/lib/components/Editor.svelte b/src/lib/components/Editor.svelte
index 4cad4d3..877025a 100644
--- a/src/lib/components/Editor.svelte
+++ b/src/lib/components/Editor.svelte
@@ -8,6 +8,7 @@
   import { spellErrorAt } from '../editor/extensions/spellCheck';
   import { spellController } from '../spell/controller';
   import TableToolbar from './TableToolbar.svelte';
+  import TableSplitDialog from './TableSplitDialog.svelte';
   import ImageToolbar from './ImageToolbar.svelte';
   import type { WrapMode } from '../editor/extensions/image';
   import { NodeSelection } from '@tiptap/pm/state';
@@ -179,6 +180,12 @@
   // Shown when the selection is inside a table; positioned just above that table.
   let tableUi = $state<{ visible: boolean; top: number; left: number }>({ visible: false, top: 0, left: 0 });
   let tableUiRaf = 0;
+  // Word-style "Split Cells…" popover, opened from the table toolbar.
+  let splitDialogOpen = $state(false);
+  // Drop the dialog if the selection leaves the table (toolbar hidden).
+  $effect(() => {
+    if (!tableUi.visible && splitDialogOpen) splitDialogOpen = false;
+  });
 
   // The DOM element of the table containing the current selection, or null.
   // nodeDOM(before(table)) returns the wrapper div the table node view renders.
@@ -628,8 +635,26 @@
       />
     </div>
   </div>
-  {#if tableUi.visible}
-    <TableToolbar {editor} top={tableUi.top} left={tableUi.left} />
+  {#if tableUi.visible && !splitDialogOpen}
+    <TableToolbar
+      {editor}
+      {tick}
+      top={tableUi.top}
+      left={tableUi.left}
+      onSplit={() => (splitDialogOpen = true)}
+    />
+  {/if}
+  {#if splitDialogOpen && tableUi.visible}
+    <TableSplitDialog
+      open={splitDialogOpen}
+      top={tableUi.top}
+      left={tableUi.left}
+      onApply={(cols, rows) => {
+        editor?.chain().focus().splitCellInto(cols, rows).run();
+        splitDialogOpen = false;
+      }}
+      onClose={() => (splitDialogOpen = false)}
+    />
   {/if}
   {#if imageUi.visible}
     <ImageToolbar {editor} top={imageUi.top} left={imageUi.left} wrap={imageUi.wrap} />
diff --git a/src/lib/components/TableSplitDialog.svelte b/src/lib/components/TableSplitDialog.svelte
new file mode 100644
index 0000000..f5822e3
--- /dev/null
+++ b/src/lib/components/TableSplitDialog.svelte
@@ -0,0 +1,152 @@
+<script lang="ts">
+  // Word/LibreOffice "Split Cells…" popover: collects column + row counts. The parent
+  // owns `open` and runs the splitCellInto command against the saved cell selection
+  // (focus moves to the inputs, like LinkDialog/TablePicker).
+  let {
+    open,
+    top,
+    left,
+    onApply,
+    onClose,
+  }: {
+    open: boolean;
+    top: number;
+    left: number;
+    onApply: (cols: number, rows: number) => void;
+    onClose: () => void;
+  } = $props();
+
+  const MIN = 1;
+  const MAX = 20;
+
+  let colsInput = $state('2');
+  let rowsInput = $state('1');
+  let firstField = $state<HTMLInputElement | null>(null);
+
+  // Reset to the defaults each time the popover opens, then focus the columns field.
+  $effect(() => {
+    if (open) {
+      colsInput = '2';
+      rowsInput = '1';
+      queueMicrotask(() => firstField?.focus());
+      queueMicrotask(() => firstField?.select());
+    }
+  });
+
+  function clamp(v: string): number {
+    const n = Math.round(parseFloat(v));
+    if (!Number.isFinite(n)) return MIN;
+    return Math.max(MIN, Math.min(MAX, n));
+  }
+
+  function apply() {
+    onApply(clamp(colsInput), clamp(rowsInput));
+  }
+
+  function onKeydown(e: KeyboardEvent) {
+    if (e.key === 'Enter') { e.preventDefault(); apply(); }
+    else if (e.key === 'Escape') { e.preventDefault(); onClose(); }
+  }
+</script>
+
+{#if open}
+  <div
+    class="split-dialog"
+    style="top: {top}px; left: {left}px;"
+    role="dialog"
+    tabindex="-1"
+    aria-label="Split cells"
+  >
+    <div class="split-fields">
+      <label>
+        <span>Columns</span>
+        <input
+          bind:this={firstField}
+          bind:value={colsInput}
+          type="number"
+          min={MIN}
+          max={MAX}
+          onkeydown={onKeydown}
+        />
+      </label>
+      <label>
+        <span>Rows</span>
+        <input
+          bind:value={rowsInput}
+          type="number"
+          min={MIN}
+          max={MAX}
+          onkeydown={onKeydown}
+        />
+      </label>
+    </div>
+    <div class="split-actions">
+      <span class="split-spacer"></span>
+      <button class="split-cancel" onclick={onClose}>Cancel</button>
+      <button class="split-apply" onclick={apply}>Split</button>
+    </div>
+  </div>
+{/if}
+
+<style>
+  .split-dialog {
+    position: absolute;
+    /* Sit just above the table's top-left corner, like TableToolbar. */
+    transform: translateY(calc(-100% - 6px));
+    z-index: 300;
+    display: flex;
+    flex-direction: column;
+    gap: 0.5rem;
+    padding: 0.6rem;
+    background: var(--color-toolbar-bg, #fff);
+    border: 1px solid var(--color-border);
+    border-radius: var(--radius);
+    box-shadow: 0 4px 16px rgba(0, 0, 0, 0.18);
+  }
+
+  .split-fields {
+    display: flex;
+    gap: 0.6rem;
+  }
+
+  label {
+    display: flex;
+    flex-direction: column;
+    gap: 0.25rem;
+    font-size: 0.75rem;
+    color: var(--color-text);
+  }
+
+  input {
+    width: 4.5rem;
+    box-sizing: border-box;
+    padding: 0.35rem 0.45rem;
+    border: 1px solid var(--color-border);
+    border-radius: var(--radius);
+    background: var(--color-surface);
+    color: var(--color-text);
+    font-size: 0.85rem;
+  }
+
+  .split-actions {
+    display: flex;
+    align-items: center;
+    gap: 0.4rem;
+  }
+
+  .split-spacer { flex: 1; }
+
+  .split-actions button {
+    height: 1.8rem;
+    padding: 0 0.7rem;
+    border: 1px solid var(--color-border);
+    border-radius: var(--radius);
+    background: transparent;
+    color: var(--color-text);
+    font-size: 0.8rem;
+    cursor: pointer;
+  }
+
+  .split-actions button:hover { background: var(--color-hover, rgba(0, 0, 0, 0.06)); }
+  .split-apply { border-color: var(--color-accent, #1a56db) !important; color: var(--color-accent, #1a56db); }
+</style>
diff --git a/src/lib/components/TableToolbar.svelte b/src/lib/components/TableToolbar.svelte
index aa01c86..3eafb45 100644
--- a/src/lib/components/TableToolbar.svelte
+++ b/src/lib/components/TableToolbar.svelte
@@ -5,10 +5,14 @@
     editor,
     top,
     left,
+    tick,
+    onSplit,
   }: {
     editor: Editor | null;
     top: number;
     left: number;
+    tick: number;
+    onSplit: () => void;
   } = $props();
 
   // Run a table command without disturbing the cell selection: preventDefault on
@@ -18,6 +22,9 @@
     if (!editor) return;
     cmd(editor.chain().focus()).run();
   }
+
+  // Merge needs a multi-cell selection; re-evaluated per transaction via `tick`.
+  const canMerge = $derived(tick >= 0 && !!editor && editor.can().mergeCells());
 </script>
 
 <div
@@ -116,6 +123,34 @@
       <path d="M3.5 5h11M7 5V3.5h4V5M5 5l.7 9.5a1 1 0 0 0 1 .9h4.6a1 1 0 0 0 1-.9L13 5" stroke="currentColor" stroke-width="1.2" stroke-linecap="round" stroke-linejoin="round"/>
     </svg>
   </button>
+
+  <span class="tt-sep"></span>
+
+  <button
+    class="tt-btn"
+    title="Merge cells"
+    aria-label="Merge cells"
+    disabled={!canMerge}
+    onclick={() => run((c) => c.mergeCells())}
+  >
+    <svg width="16" height="16" viewBox="0 0 18 18" fill="none" aria-hidden="true">
+      <rect x="3" y="4" width="12" height="10" rx="1" stroke="currentColor" stroke-width="1.3"/>
+      <path d="M6 9h6M6 9l1.6-1.6M6 9l1.6 1.6M12 9l-1.6-1.6M12 9l-1.6 1.6" stroke="currentColor" stroke-width="1.2" stroke-linecap="round" stroke-linejoin="round"/>
+    </svg>
+  </button>
+
+  <button
+    class="tt-btn"
+    title="Split cells…"
+    aria-label="Split cells"
+    onclick={() => onSplit()}
+  >
+    <svg width="16" height="16" viewBox="0 0 18 18" fill="none" aria-hidden="true">
+      <rect x="3" y="4" width="12" height="10" rx="1" stroke="currentColor" stroke-width="1.3"/>
+      <line x1="9" y1="4" x2="9" y2="14" stroke="currentColor" stroke-width="1.3"/>
+      <path d="M9 7.4L7.4 9 9 10.6M9 7.4L10.6 9 9 10.6" stroke="currentColor" stroke-width="1.1" stroke-linecap="round" stroke-linejoin="round"/>
+    </svg>
+  </button>
 </div>
 
 <style>
@@ -152,10 +187,15 @@
     transition: background 0.12s, color 0.12s;
   }
 
-  .tt-btn:hover {
+  .tt-btn:hover:not(:disabled) {
     background: var(--color-btn-hover);
   }
 
+  .tt-btn:disabled {
+    opacity: 0.35;
+    cursor: default;
+  }
+
   .tt-danger:hover {
     background: #fdecea;
     color: #c0392b;
diff --git a/src/lib/editor/extensions.ts b/src/lib/editor/extensions.ts
index e9ff0ef..767ef6d 100644
--- a/src/lib/editor/extensions.ts
+++ b/src/lib/editor/extensions.ts
@@ -33,6 +33,7 @@ import { SearchReplace } from './extensions/searchReplace';
 import { TableView } from './extensions/tableView';
 import { TableColumnResize } from './extensions/tableColumnResize';
 import { TableRowResize } from './extensions/tableRowResize';
+import { TableSplit } from './extensions/tableSplit';
 import { TrailingNode } from './extensions/trailingNode';
 import { Image } from './extensions/image';
 
@@ -79,6 +80,8 @@ export const extensions = [
   TableCell,
   TableColumnResize,
   TableRowResize,
+  // Word-style "Split Cells…" (N×M); merge uses extension-table's built-in mergeCells.
+  TableSplit,
   // Guarantees a paragraph after a trailing table so the cursor isn't trapped
   // and the user can keep writing below a table at the document's end.
   TrailingNode,
diff --git a/src/lib/editor/extensions/tableSplit.ts b/src/lib/editor/extensions/tableSplit.ts
new file mode 100644
index 0000000..9add484
--- /dev/null
+++ b/src/lib/editor/extensions/tableSplit.ts
@@ -0,0 +1,230 @@
+import { Extension } from '@tiptap/core';
+import type { CommandProps } from '@tiptap/core';
+import { TextSelection } from '@tiptap/pm/state';
+import type { Node as PMNode } from '@tiptap/pm/model';
+import { TableMap, selectedRect, isInTable } from '@tiptap/pm/tables';
+import { columnWeightsFromRow } from './tableView';
+
+// Word/LibreOffice "Split Cells…": divide the current cell (or a clean rectangular
+// cell selection) into `cols` × `rows` sub-cells. prosemirror-tables only ships
+// splitCell (un-merge), so this is custom. The table is a strict rectangular grid,
+// so adding sub-columns/rows means inserting grid lines and letting every other
+// cell that crosses a new line grow its span (bridge) — exactly what Word does.
+// Implemented by reading the grid via TableMap, expanding it, partitioning the
+// cell's region, and rebuilding the table node in one step.
+
+declare module '@tiptap/core' {
+  interface Commands<ReturnType> {
+    tableSplit: {
+      splitCellInto: (cols: number, rows: number) => ReturnType;
+    };
+  }
+}
+
+const MAX_SPLIT = 50;
+
+function clampCount(n: number): number {
+  if (!Number.isFinite(n)) return 1;
+  return Math.max(1, Math.min(MAX_SPLIT, Math.round(n)));
+}
+
+// Contiguous group sizes splitting `total` into `parts` (first `rem` are one larger),
+// returned as prefix offsets of length parts+1.
+function groupOffsets(total: number, parts: number): number[] {
+  const base = Math.floor(total / parts);
+  const rem = total % parts;
+  const offsets = [0];
+  for (let i = 0; i < parts; i++) offsets.push(offsets[i] + base + (i < rem ? 1 : 0));
+  return offsets;
+}
+
+// Resolve the first row's proportional weights (nulls → average present, all-null → 1).
+function resolveColWeights(table: PMNode, width: number): number[] {
+  const raw = columnWeightsFromRow(table.firstChild);
+  const present = raw.filter((w): w is number => w != null && w > 0);
+  const avg = present.length ? present.reduce((a, b) => a + b, 0) / present.length : 1;
+  const out: number[] = [];
+  for (let c = 0; c < width; c++) {
+    const w = raw[c];
+    out.push(w != null && w > 0 ? w : avg);
+  }
+  return out;
+}
+
+export function splitCellInto(colsArg: number, rowsArg: number) {
+  return ({ state, tr, dispatch }: CommandProps): boolean => {
+    if (!isInTable(state)) return false;
+    const cols = clampCount(colsArg);
+    const rows = clampCount(rowsArg);
+
+    const rect = selectedRect(state);
+    const { map, table, tableStart } = rect;
+    const W = map.width;
+    const H = map.height;
+
+    // ── Build the owner grid: owner[r][c] = index into `cells` (distinct cells). ──
+    const cells: { node: PMNode }[] = [];
+    const posToIdx = new Map<number, number>();
+    const owner: number[][] = [];
+    for (let r = 0; r < H; r++) {
+      const rowArr: number[] = [];
+      for (let c = 0; c < W; c++) {
+        const pos = map.map[r * W + c];
+        let idx = posToIdx.get(pos);
+        if (idx === undefined) {
+          idx = cells.length;
+          posToIdx.set(pos, idx);
+          cells.push({ node: table.nodeAt(pos)! });
+        }
+        rowArr.push(idx);
+      }
+      owner.push(rowArr);
+    }
+
+    // Selection region (single cell for a cursor; bounding box for a CellSelection).
+    const rTop = rect.top, rLeft = rect.left, rBottom = rect.bottom, rRight = rect.right;
+
+    // Refuse a region whose border cuts a spanning cell (mergeCells does the same):
+    // every distinct cell touching the region must be fully contained in it.
+    const cellBounds = new Map<number, { top: number; left: number; bottom: number; right: number }>();
+    for (let r = 0; r < H; r++) {
+      for (let c = 0; c < W; c++) {
+        const idx = owner[r][c];
+        const b = cellBounds.get(idx);
+        if (!b) cellBounds.set(idx, { top: r, left: c, bottom: r + 1, right: c + 1 });
+        else { b.bottom = Math.max(b.bottom, r + 1); b.right = Math.max(b.right, c + 1); }
+      }
+    }
+    for (let r = rTop; r < rBottom; r++) {
+      for (let c = rLeft; c < rRight; c++) {
+        const b = cellBounds.get(owner[r][c])!;
+        if (b.top < rTop || b.left < rLeft || b.bottom > rBottom || b.right > rRight) return false;
+      }
+    }
+
+    if (!dispatch) return true;
+
+    // Content for the first sub-cell: all cells in the region, in row-major origin
+    // order (a single cell normally; a multi-cell selection concatenates — merge).
+    const targetNode = cells[owner[rTop][rLeft]].node;
+    const combined: PMNode[] = [];
+    const seen = new Set<number>();
+    for (let r = rTop; r < rBottom; r++) {
+      for (let c = rLeft; c < rRight; c++) {
+        const idx = owner[r][c];
+        if (seen.has(idx)) continue;
+        seen.add(idx);
+        cells[idx].node.content.forEach((n) => combined.push(n));
+      }
+    }
+
+    // ── Expand the grid so the region is regionCols × regionRows. ──
+    const regionCols = Math.max(cols, rRight - rLeft);
+    const regionRows = Math.max(rows, rBottom - rTop);
+    const addCols = regionCols - (rRight - rLeft);
+    const addRows = regionRows - (rBottom - rTop);
+
+    const colWeights = resolveColWeights(table, W);
+    const rowSource = Array.from({ length: H }, (_, r) => r); // expanded row → original row
+
+    // Duplicate the region's right-edge column: cells crossing it grow (bridge).
+    if (addCols > 0) {
+      for (let r = 0; r < H; r++) {
+        const fill = Array(addCols).fill(owner[r][rRight - 1]);
+        owner[r].splice(rRight, 0, ...fill);
+      }
+      colWeights.splice(rRight, 0, ...Array(addCols).fill(colWeights[rRight - 1]));
+    }
+    const W2 = W + addCols;
+
+    // Duplicate the region's bottom-edge row: cells crossing it grow (bridge).
+    if (addRows > 0) {
+      const tmpl = owner[rBottom - 1];
+      for (let k = 0; k < addRows; k++) {
+        owner.splice(rBottom, 0, tmpl.slice());
+        rowSource.splice(rBottom, 0, rowSource[rBottom - 1]);
+      }
+    }
+    const H2 = H + addRows;
+
+    // ── Overwrite the region with cols×rows new sub-cells. ──
+    const colOff = groupOffsets(regionCols, cols);
+    const rowOff = groupOffsets(regionRows, rows);
+    let first = true;
+    const subContent = new Map<number, PMNode[] | null>(); // idx → content (null = empty)
+    for (let gj = 0; gj < rows; gj++) {
+      for (let gi = 0; gi < cols; gi++) {
+        const idx = cells.length;
+        cells.push({ node: targetNode }); // node only used for type/attrs of the cell
+        subContent.set(idx, first ? combined : null);
+        first = false;
+        const cStart = rLeft + colOff[gi], cEnd = rLeft + colOff[gi + 1];
+        const rStart = rTop + rowOff[gj], rEnd = rTop + rowOff[gj + 1];
+        for (let r = rStart; r < rEnd; r++)
+          for (let c = cStart; c < cEnd; c++) owner[r][c] = idx;
+      }
+    }
+
+    // Redistribute the region columns so each column-group sums to regionTotal/cols
+    // (equal sub-cells, table width preserved).
+    let regionTotal = 0;
+    for (let c = rLeft; c < rLeft + regionCols; c++) regionTotal += colWeights[c];
+    const perGroup = regionTotal / cols;
+    for (let gi = 0; gi < cols; gi++) {
+      const sz = colOff[gi + 1] - colOff[gi];
+      for (let c = rLeft + colOff[gi]; c < rLeft + colOff[gi + 1]; c++) colWeights[c] = perGroup / sz;
+    }
+    // Normalize to integer basis points (ratios only; matches the colwidth contract).
+    const wTotal = colWeights.reduce((a, b) => a + b, 0) || 1;
+    const intWeights = colWeights.map((w) => Math.max(1, Math.round((w / wTotal) * 10000)));
+
+    // ── Serialize the grid back into a table node. ──
+    const schema = state.schema;
+    const rowType = table.child(0).type;
+    const newRows: PMNode[] = [];
+    for (let r = 0; r < H2; r++) {
+      const cellNodes: PMNode[] = [];
+      for (let c = 0; c < W2; c++) {
+        const idx = owner[r][c];
+        const isOrigin = (r === 0 || owner[r - 1][c] !== idx) && (c === 0 || owner[r][c - 1] !== idx);
+        if (!isOrigin) continue;
+        let colspan = 1;
+        while (c + colspan < W2 && owner[r][c + colspan] === idx) colspan++;
+        let rowspan = 1;
+        while (r + rowspan < H2 && owner[r + rowspan][c] === idx) rowspan++;
+        const colwidth = intWeights.slice(c, c + colspan);
+        const src = cells[idx].node;
+        const attrs = { ...src.attrs, colspan, rowspan, colwidth };
+        if (subContent.has(idx)) {
+          const content = subContent.get(idx);
+          cellNodes.push(content && content.length ? src.type.create(attrs, content) : src.type.createAndFill(attrs)!);
+        } else {
+          cellNodes.push(src.type.create(attrs, src.content));
+        }
+      }
+      newRows.push(rowType.create(table.child(rowSource[r]).attrs, cellNodes));
+    }
+    const newTable = table.type.create(table.attrs, newRows);
+
+    const tablePos = tableStart - 1;
+    const tableEnd = tablePos + table.nodeSize;
+    tr.replaceWith(tablePos, tableEnd, newTable);
+
+    // Caret into the first sub-cell.
+    const newMap = TableMap.get(newTable);
+    const cellPos = tablePos + 1 + newMap.positionAt(rTop, rLeft, newTable);
+    tr.setSelection(TextSelection.near(tr.doc.resolve(cellPos + 1)));
+    dispatch(tr);
+    return true;
+  };
+}
+
+export const TableSplit = Extension.create({
+  name: 'tableSplit',
+
+  addCommands() {
+    return {
+      splitCellInto: (cols: number, rows: number) => splitCellInto(cols, rows),
+    };
+  },
+});
diff --git a/src/lib/export/odt.ts b/src/lib/export/odt.ts
index c7bc244..89be944 100644
--- a/src/lib/export/odt.ts
+++ b/src/lib/export/odt.ts
@@ -1,4 +1,4 @@
-import { tiptapToOdt, type TiptapNode, type TextFormatting, type OdtDocument, type ParagraphBuilder, type TableBuilder, type RowBuilder, type CellBuilder, type HeaderFooterBuilder } from 'odf-kit';
+import { tiptapToOdt, type TiptapNode, type TextFormatting, type OdtDocument, type ParagraphBuilder, type TableBuilder, type RowBuilder, type CellBuilder, type CellOptions, type HeaderFooterBuilder } from 'odf-kit';
 import { unzipSync, zipSync, strFromU8, strToU8 } from 'fflate';
 import { DEFAULT_MARGINS, type PageMargins } from '../storage/pageMargins';
 import type { Orientation } from '../storage/pageOrientation';
@@ -1095,9 +1095,17 @@ function exportTable(node: TiptapNode, doc: OdtDocument, contentWidthCm: number,
           // Emit the cell's runs (SEG-separated) and record its block descriptor.
           // addCell runs synchronously, so the push is in document order — matching
           // how applyCellBlocks later walks cells in content.xml.
+          // colSpan/rowSpan make odf-kit emit number-columns/rows-spanned and the
+          // <table:covered-table-cell> placeholders; those never match the
+          // applyCellBlocks cell regex, so cellBlocks stays one-per-real-cell aligned.
+          const opts: CellOptions = { padding: CELL_PADDING };
+          const colspan = (cell.attrs?.colspan as number) ?? 1;
+          const rowspan = (cell.attrs?.rowspan as number) ?? 1;
+          if (colspan > 1) opts.colSpan = colspan;
+          if (rowspan > 1) opts.rowSpan = rowspan;
           r.addCell((c: CellBuilder) => {
             cellBlocks.push(buildCellContent(cell, c));
-          }, { padding: CELL_PADDING });
+          }, opts);
         }
       });
     }
diff --git a/tests/roundtrip.test.ts b/tests/roundtrip.test.ts
index cb87b13..f41da68 100644
--- a/tests/roundtrip.test.ts
+++ b/tests/roundtrip.test.ts
@@ -2,7 +2,7 @@
 // plus a hand-crafted LibreOffice/Word-style .odt exercising the style resolver.
 // jsdom (vitest `environment`) supplies the global DOMParser.
 import { describe, it, expect } from 'vitest';
-import { zipSync, strToU8 } from 'fflate';
+import { zipSync, strToU8, unzipSync, strFromU8 } from 'fflate';
 import { getSchema } from '@tiptap/core';
 import { Node as PMNode } from '@tiptap/pm/model';
 import { buildOdt } from '../src/lib/export/odt';
@@ -23,6 +23,9 @@ const H = (attrs: N, ...content: N[]): N => ({ type: 'heading', attrs, ...(conte
 const LI = (...content: N[]): N => ({ type: 'listItem', content });
 const CELL = (colwidth: number[] | null, ...content: N[]): N =>
   ({ type: 'tableCell', attrs: { colspan: 1, rowspan: 1, colwidth }, content });
+const CELLM = (colspan: number, rowspan: number, colwidth: number[] | null, text: string): N =>
+  ({ type: 'tableCell', attrs: { colspan, rowspan, colwidth }, content: [P(null, T(text))] });
+const ROW = (...cells: N[]): N => ({ type: 'tableRow', content: cells });
 
 // A tiny valid PNG; only its bytes matter for the round-trip (no image decoding).
 const PNG = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAC0lEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg==';
@@ -236,6 +239,45 @@ describe('Leg 1: editor → buildOdt → importOdt', () => {
   });
 });
 
+describe('Leg 1b: merged table cells (colspan/rowspan)', () => {
+  // 3×3 grid: A spans 2 cols (row 0); C spans 2 rows (col 0, rows 1–2).
+  //   row0: [A A][B]    row1: [C][D][E]    row2: [C][F][G]
+  const mergedDoc: N = {
+    type: 'doc',
+    content: [
+      P(null, T('Merged cells:')),
+      { type: 'table', content: [
+        ROW(CELLM(2, 1, [100, 100], 'A'), CELLM(1, 1, [100], 'B')),
+        ROW(CELLM(1, 2, [100], 'C'), CELLM(1, 1, [100], 'D'), CELLM(1, 1, [100], 'E')),
+        ROW(CELLM(1, 1, [100], 'F'), CELLM(1, 1, [100], 'G')),
+      ] },
+    ],
+  };
+
+  it('exports spans + covered cells and re-imports them', async () => {
+    const bytes = await buildOdt(mergedDoc, margins, 'portrait');
+    const content = strFromU8(unzipSync(bytes)['content.xml']);
+    check('content.xml emits number-columns-spanned=2', content.includes('table:number-columns-spanned="2"'));
+    check('content.xml emits number-rows-spanned=2', content.includes('table:number-rows-spanned="2"'));
+    check('content.xml emits a covered-table-cell', content.includes('<table:covered-table-cell'));
+
+    const res = importOdt(bytes);
+    check('no warnings on own export', res.warnings.length === 0, res.warnings);
+    const table = (res.content.content ?? []).find((n: N) => n.type === 'table');
+    const rows = table?.content ?? [];
+    check('row 0 has 2 cells', rows[0]?.content?.length === 2, rows[0]?.content?.length);
+    check('row 1 has 3 cells', rows[1]?.content?.length === 3, rows[1]?.content?.length);
+    check('row 2 has 2 cells (covered slot skipped)', rows[2]?.content?.length === 2, rows[2]?.content?.length);
+    check('A has colspan 2', rows[0]?.content?.[0]?.attrs?.colspan === 2, rows[0]?.content?.[0]?.attrs);
+    check('C has rowspan 2', rows[1]?.content?.[0]?.attrs?.rowspan === 2, rows[1]?.content?.[0]?.attrs);
+
+    const textOf = (cell: N) => cell?.content?.[0]?.content?.[0]?.text;
+    check('A text preserved', textOf(rows[0]?.content?.[0]) === 'A', textOf(rows[0]?.content?.[0]));
+    check('F at col 1 of row 2', textOf(rows[2]?.content?.[0]) === 'F', textOf(rows[2]?.content?.[0]));
+    check('G at col 2 of row 2', textOf(rows[2]?.content?.[1]) === 'G', textOf(rows[2]?.content?.[1]));
+  });
+});
+
 describe('Leg 2: foreign (LibreOffice/Word-style) .odt → importOdt', () => {
   it('resolves named/automatic styles, repeated cells, lists, and reports degradations', () => {
     const stylesXml = `<?xml version="1.0" encoding="UTF-8"?>
diff --git a/tests/unit/table-split.test.ts b/tests/unit/table-split.test.ts
new file mode 100644
index 0000000..ad4e4fc
--- /dev/null
+++ b/tests/unit/table-split.test.ts
@@ -0,0 +1,95 @@
+// Unit test for the custom splitCellInto command: drives it against a ProseMirror
+// EditorState (no DOM/Editor needed) and inspects the rebuilt table. Covers the
+// two Word/LibreOffice cases: splitting a plain cell (adds grid lines + bridges
+// neighbours) and splitting a merged cell (un-merge).
+import { describe, it, expect } from 'vitest';
+import { getSchema } from '@tiptap/core';
+import { EditorState, TextSelection } from '@tiptap/pm/state';
+import type { Node as PMNode } from '@tiptap/pm/model';
+import Document from '@tiptap/extension-document';
+import Paragraph from '@tiptap/extension-paragraph';
+import Text from '@tiptap/extension-text';
+import { Table, TableHeader, TableCell } from '@tiptap/extension-table';
+import { ResizableTableRow } from '../../src/lib/editor/extensions/tableRow';
+import { splitCellInto } from '../../src/lib/editor/extensions/tableSplit';
+
+type N = any;
+
+const schema = getSchema([Document, Paragraph, Text, Table, ResizableTableRow, TableCell, TableHeader]);
+
+const cell = (text: string, colspan = 1, rowspan = 1): N => ({
+  type: 'tableCell',
+  attrs: { colspan, rowspan, colwidth: null },
+  content: [{ type: 'paragraph', content: text ? [{ type: 'text', text }] : [] }],
+});
+const row = (...cells: N[]): N => ({ type: 'tableRow', content: cells });
+const docJSON = (...rows: N[]): N => ({ type: 'doc', content: [{ type: 'table', content: rows }] });
+
+// Run splitCellInto(cols,rows) with the cursor in the cell containing `targetText`.
+function runSplit(json: N, targetText: string, cols: number, rows: number): N {
+  const doc = schema.nodeFromJSON(json);
+  let textPos = -1;
+  doc.descendants((node: PMNode, pos: number) => {
+    if (node.isText && node.text === targetText) textPos = pos;
+  });
+  if (textPos < 0) throw new Error(`target text ${targetText} not found`);
+  const state = EditorState.create({ schema, doc, selection: TextSelection.create(doc, textPos) });
+  let next: EditorState | null = null;
+  const ok = splitCellInto(cols, rows)({
+    state,
+    tr: state.tr,
+    dispatch: (tr) => { next = state.apply(tr); },
+  } as any);
+  expect(ok).toBe(true);
+  return next!.doc.toJSON().content[0]; // the table node
+}
+
+const cellText = (c: N): string | undefined => c?.content?.[0]?.content?.[0]?.text;
+
+describe('splitCellInto', () => {
+  it('splits a plain cell into 2×2, bridging the neighbouring cells', () => {
+    // 2×2 grid; split the top-left cell ("A") into 2 cols × 2 rows.
+    const table = runSplit(
+      docJSON(row(cell('A'), cell('B')), row(cell('C'), cell('D'))),
+      'A', 2, 2,
+    );
+    const rows = table.content;
+    expect(rows.length).toBe(3);
+    // row0: [A][new][B rowspan2]
+    expect(rows[0].content.length).toBe(3);
+    expect(cellText(rows[0].content[0])).toBe('A');
+    expect(rows[0].content[2].attrs.rowspan).toBe(2); // top-right bridges down
+    expect(cellText(rows[0].content[2])).toBe('B');
+    // row1: the 2 new sub-cells (col2 covered by B's rowspan)
+    expect(rows[1].content.length).toBe(2);
+    // row2: [C colspan2][D]
+    expect(rows[2].content.length).toBe(2);
+    expect(rows[2].content[0].attrs.colspan).toBe(2); // bottom-left bridges right
+    expect(cellText(rows[2].content[0])).toBe('C');
+    expect(cellText(rows[2].content[1])).toBe('D');
+  });
+
+  it('un-merges a merged cell (colspan 2 → two cells)', () => {
+    // Row0 is one merged cell spanning 2 cols; row1 has two cells.
+    const table = runSplit(
+      docJSON(row(cell('M', 2, 1)), row(cell('X'), cell('Y'))),
+      'M', 2, 1,
+    );
+    const rows = table.content;
+    expect(rows.length).toBe(2);
+    expect(rows[0].content.length).toBe(2); // M split back into two
+    expect(rows[0].content[0].attrs.colspan).toBe(1);
+    expect(rows[0].content[1].attrs.colspan).toBe(1);
+    expect(cellText(rows[0].content[0])).toBe('M'); // content kept in the first
+  });
+
+  it('splits a single cell into 3 columns', () => {
+    const table = runSplit(docJSON(row(cell('A'), cell('B'))), 'A', 3, 1);
+    const rows = table.content;
+    expect(rows.length).toBe(1);
+    // A → 3 sub-cells, plus B (now bridged): 4 cells across a 4-col grid.
+    expect(rows[0].content.length).toBe(4);
+    expect(cellText(rows[0].content[0])).toBe('A');
+    expect(cellText(rows[0].content[3])).toBe('B');
+  });
+});