fix: markdown tables drop empty cells and misalign columns (#1164)

* refactor: extract splitTableRow helper for markdown tables

* fix: keep empty interior cells in markdown tables to preserve columns

* test: splitTableRow keeps empty interior cells

static/js/markdown.js

@@ -5,6 +5,7 @@
  */
 
 import uiModule from './ui.js';
+import { splitTableRow } from './markdown/tableRow.js';
 
 var escapeHtml = uiModule.esc;
 
@@ -535,7 +536,7 @@ export function mdToHtml(src) {
     let html = '<table style="border-collapse: collapse; width: 100%; margin: 10px 0;">';
 
     rows.forEach((row, idx) => {
-      const cells = row.split('|').filter(cell => cell.trim() !== '');
+      const cells = splitTableRow(row);
       if (cells.length === 0) return;
 
       html += idx === 1 ? '<tbody>' : '';

static/js/markdown/tableRow.js

@@ -0,0 +1,18 @@
+// static/js/markdown/tableRow.js
+//
+// Pure helper for splitting a markdown table row into cells. No DOM —
+// safe to import anywhere and to unit-test under node.
+
+// Split a "| a | b | c |" row into trimmed cell strings.
+//
+// Strip only the optional leading/trailing pipe, then split — filtering out
+// every empty cell (the old behaviour) dropped intentionally-empty interior
+// cells too, so "| a |  | c |" collapsed to 2 columns and misaligned with the
+// header.
+export function splitTableRow(row) {
+  return (row || '')
+    .replace(/^\s*\|/, '')
+    .replace(/\|\s*$/, '')
+    .split('|')
+    .map((cell) => cell.trim());
+}