fix(equations): preserve LaTeX row-break dimensions in sub-equation tagging

- Update the sub-equation row split logic in live-preview-equations to use a capturing regex `/(\\\\(?:\s*\[[^\]]*\])?)/`.
- Reconstruct the equation parts by only tagging the math content and preserving the separators (e.g. `\\[0.6em]`) exactly as-is.
- Add unit tests verifying both standard and dimensioned row breaks.

esbuild.config.mjs

@@ -5,7 +5,6 @@ import fs from 'fs';
 import path from 'path';
 import inlineWorkerPlugin from 'esbuild-plugin-inline-worker';
 
-
 const builtins = [
   ...new Set([...builtinModules, ...builtinModules.map(moduleName => `node:${moduleName}`)])
 ];

src/core/equations/live-preview-equations.ts

@@ -264,27 +264,33 @@ function createTagManagerPlugin(
           // --- Mode 1: Sub-equation ---
           if (info.subIndices && info.subIndices.size > 0 && info.printName) {
             const baseName = info.printName.slice(1, -1);
-            const rows = mathPart.trim().split(/\\\\/);
+            const parts = mathPart.trim().split(/(\\\\(?:\s*\[[^\]]*\])?)/);
             let hasContent = false;
+            const newParts = [...parts];
 
-            const taggedRows = rows.map((row, index) => {
+            for (let i = 0; i < parts.length; i += 2) {
+              const row = parts[i];
               const cleanedRow = row.replace(/^[ \t]+/, '');
-              if (cleanedRow.trim() === '') return cleanedRow;
+              if (cleanedRow.trim() === '') {
+                newParts[i] = cleanedRow;
+                continue;
+              }
               hasContent = true;
-              const subIndex = index + 1;
+              const subIndex = i / 2 + 1;
               const newTag = ` \\tag{${baseName}.${subIndex}}`;
               const endEnvMatch = cleanedRow.match(/(\\end\{[a-zA-Z*]+\})/);
               if (endEnvMatch && endEnvMatch.index !== undefined) {
                 const before = cleanedRow.substring(0, endEnvMatch.index).trimEnd();
                 const environment = endEnvMatch[0];
                 const after = cleanedRow.substring(endEnvMatch.index + environment.length);
-                return `${before + newTag} ${environment}${after}`;
+                newParts[i] = `${before + newTag} ${environment}${after}`;
+              } else {
+                newParts[i] = cleanedRow.trimEnd() + newTag;
               }
-              return cleanedRow.trimEnd() + newTag;
-            });
+            }
 
             if (hasContent) {
-              newInnerContent = taggedRows.join(' \\\\ ');
+              newInnerContent = newParts.join('');
             }
           }
           // --- Mode 2: Normal Equation ---

test_helpers/utils.test.ts

@@ -113,3 +113,22 @@ describe('general.ts tests', () => {
     expect(arr).toEqual([1, 99, 2, 3]);
   });
 });
+
+describe('Sub-equation splitting regex tests', () => {
+  it('should split rows while keeping \\[dimen] intact', () => {
+    const regex = /(\\\\(?:\s*\[[^\]]*\])?)/;
+    const input = `\\beta \\frac{\\partial P}{\\partial \\rho} & = \\frac{\\partial}{\\partial \\eta} \\left[ \\eta \\frac{1 + \\eta + \\eta^2}{(1 - \\eta)^3} \\right]  \\\\[0.6em]\n\\implies q(\\eta)  & = \\frac{(1 + 2\\eta)^2}{(1 - \\eta)^4}  \\end{align}`;
+    const parts = input.split(regex);
+    expect(parts.length).toBe(3);
+    expect(parts[0]).toContain('\\beta');
+    expect(parts[1]).toBe('\\\\[0.6em]');
+    expect(parts[2]).toContain('\\implies');
+  });
+
+  it('should split rows when there is no dimension parameter', () => {
+    const regex = /(\\\\(?:\s*\[[^\]]*\])?)/;
+    const input = `row1 \\\\ row2`;
+    const parts = input.split(regex);
+    expect(parts).toEqual(['row1 ', '\\\\', ' row2']);
+  });
+});