fix: a vertically merged cell keeps the edges of the rows it covers

A cell's grid box claimed one row, so a w:vMerge reaching the table's last
row sat inside the banded region instead of on its bottom edge — and a band
declaring insideH nil then dropped the line. The merge extent is counted
before the covered rows are read.

Measured against LibreOffice: the bottom rule runs the full width under a
merged first column, which the editor now draws too.

src/lib/import/CLAUDE.md

@@ -59,7 +59,10 @@ which is where an assigned style's regions otherwise come from. An area covers a
 its `top`/`bottom`/`left`/`right` apply where the cell sits on that box's edge, its
 `insideH`/`insideV` anywhere within. A **band's box is the whole banded region**, not the
 one row it shades — that is what makes `insideH` the line *between* two band rows, which
-is how a style with no inner rules (Word's Medium Shading) comes out borderless. Areas
+is how a style with no inner rules (Word's Medium Shading) comes out borderless. A cell's
+own box spans the rows its `w:vMerge` covers — counted ahead of the covered rows
+(`vMergeRows`) — or a merge reaching the last row loses its bottom edge to that same rule.
+Areas
 layer in Word's ascending precedence, over the table's borders and under the cell's own
 `w:tcPr`; banding counts from the first *body* row, so the row under a header row is band 1.
 `w:tblLook` decides which areas apply at all — named flags where the file has them, the

src/lib/import/docx.ts

@@ -1704,6 +1704,28 @@ function condAreasFor(
   return out;
 }
 
+// How many rows a vertically merged cell covers. Its box has to say so before the covered
+// rows are read, or a merge reaching the table's last row reads as an inside line there —
+// which a style whose band declares insideH nil then drops.
+function vMergeRows(trs: Element[], from: number, col: number): number {
+  let n = 1;
+  for (let ri = from + 1; ri < trs.length; ri++) {
+    let c = 0;
+    let covered = false;
+    for (const tc of fcAll(trs[ri], 'tc')) {
+      if (c >= col) {
+        const el = fc(fc(tc, 'tcPr'), 'vMerge');
+        covered = c === col && !!el && (wVal(el) ?? 'continue') !== 'restart';
+        break;
+      }
+      c += intAttr(fc(fc(tc, 'tcPr'), 'gridSpan'), W, 'val') ?? 1;
+    }
+    if (!covered) break;
+    n++;
+  }
+  return n;
+}
+
 // Which side of an area a cell's edge is: its own outer side where the cell sits on the
 // area's edge, the area's inside line otherwise.
 function areaSide(area: GridBox, cell: GridBox, side: 'top' | 'bottom' | 'left' | 'right'): string {
@@ -1825,7 +1847,8 @@ function buildTable(tbl: Element, ctx: Ctx): Node | null {
         col += colspan;
         continue; // covered cell — dropped, span folded into its origin
       }
-      const box: GridBox = { row: ri, col, rowEnd: ri + 1, colEnd: col + colspan };
+      const rowEnd = ri + (vMerge === 'restart' ? vMergeRows(trs, ri, col) : 1);
+      const box: GridBox = { row: ri, col, rowEnd, colEnd: col + colspan };
       const areas = conds.size ? condAreasFor(conds, flags, band, box, trs.length, gridCols) : [];
       const paint = condPaint(areas);
       const fill = fc(tcPr, 'shd')?.getAttributeNS(W, 'fill');

tests/unit/docx-table-style.test.ts

@@ -40,6 +40,17 @@ const table = (look = '<w:tblLook w:firstRow="1" w:firstColumn="1" w:noHBand="0"
     `<w:tr>${[0, 1].map((c) => `<w:tc><w:p><w:r><w:t>r${r}c${c}</w:t></w:r></w:p></w:tc>`).join('')}</w:tr>`,
   ).join('') + '</w:tbl>';
 
+// The same grid with its first column merged from the first body row down to the last.
+const mergedTable = () =>
+  `<w:tbl><w:tblPr><w:tblStyle w:val="Banded"/><w:tblLook w:firstRow="1" w:firstColumn="1" w:noHBand="0" w:noVBand="1"/></w:tblPr>
+   <w:tblGrid><w:gridCol w:w="4000"/><w:gridCol w:w="4000"/></w:tblGrid>` +
+  [0, 1, 2, 3].map((r) => {
+    const merge = r === 1 ? '<w:vMerge w:val="restart"/>' : '<w:vMerge/>';
+    const first = r === 0 ? '<w:tc><w:p><w:r><w:t>h</w:t></w:r></w:p></w:tc>'
+      : `<w:tc><w:tcPr>${merge}</w:tcPr><w:p><w:r><w:t>m</w:t></w:r></w:p></w:tc>`;
+    return `<w:tr>${first}<w:tc><w:p><w:r><w:t>r${r}</w:t></w:r></w:p></w:tc></w:tr>`;
+  }).join('') + '</w:tbl>';
+
 const docxWith = (body: string) =>
   zipSync({
     'word/document.xml': strToU8(`<?xml version="1.0"?><w:document xmlns:w="${W}"><w:body>${body}</w:body></w:document>`),
@@ -77,6 +88,12 @@ describe('a Word table style paints its conditional areas', () => {
     expect(rows[3][0].attrs.borderBottom).toBe('1pt solid #4F81BD'); // the table's own edge
   });
 
+  it('gives a merged cell the edges of every row it covers', () => {
+    const merged = cellsOf(docxWith(mergedTable()));
+    expect(merged[1][0].attrs.rowspan).toBe(3);
+    expect(merged[1][0].attrs.borderBottom).toBe('1pt solid #4F81BD'); // the table's own edge
+  });
+
   it('paints nothing the table’s look switches off', () => {
     const off = cellsOf(docxWith(table('<w:tblLook w:firstRow="0" w:firstColumn="0" w:noHBand="1" w:noVBand="1"/>')));
     expect(off[0][0].attrs.backgroundColor).toBeUndefined();