fix(compare-rendering): scope JSON_END search and resolve REPO_ROOT via fileURLToPath

Two small fixes from PR review:

- parseExtractionOutput searched for JSON_END from offset 0, so a
  document whose paragraph text contained the literal string
  "JSON_END" could truncate the payload before JSON.parse. Search
  from past JSON_BEGIN instead.
- REPO_ROOT in superdoc.ts was using URL.pathname, which yields
  /C:/… on Windows and keeps URL-encoded special chars. Use
  fileURLToPath like we already do in cache.ts / word.ts.

Author: caio-pizzol

devtools/compare-rendering/src/superdoc.ts

@@ -2,6 +2,7 @@ import { spawn } from 'node:child_process';
 import { mkdtemp, readFile, rm } from 'node:fs/promises';
 import { tmpdir } from 'node:os';
 import { join } from 'node:path';
+import { fileURLToPath } from 'node:url';
 
 type SuperDocSnapshot = {
   layoutSnapshot: {
@@ -29,7 +30,7 @@ export type SuperDocExtraction = {
   pageCount: number;
 };
 
-const REPO_ROOT = new URL('../../../', import.meta.url).pathname;
+const REPO_ROOT = fileURLToPath(new URL('../../../', import.meta.url));
 
 export async function extractSuperDoc(
   docxPath: string,

devtools/compare-rendering/src/word.ts

@@ -61,11 +61,15 @@ async function runPowerShell(script: string, timeoutSeconds: number): Promise<st
 
 function parseExtractionOutput(output: string): WordExtraction {
   const begin = output.indexOf('JSON_BEGIN');
-  const end = output.indexOf('JSON_END');
-  if (begin === -1 || end === -1) {
-    throw new Error(`extract-layout.ps1: missing JSON markers\n${output.slice(0, 800)}`);
+  if (begin === -1) {
+    throw new Error(`extract-layout.ps1: missing JSON_BEGIN marker\n${output.slice(0, 800)}`);
   }
-  const json = output.slice(begin + 'JSON_BEGIN'.length, end).trim();
+  const payloadStart = begin + 'JSON_BEGIN'.length;
+  const end = output.indexOf('JSON_END', payloadStart);
+  if (end === -1) {
+    throw new Error(`extract-layout.ps1: missing JSON_END marker\n${output.slice(0, 800)}`);
+  }
+  const json = output.slice(payloadStart, end).trim();
   return JSON.parse(json) as WordExtraction;
 }