refactor(app): migrate to ESM; preload emitted as CJS for sandbox (Phase 5d-3b)

App source (main/preload/worker/renderer) -> ESM; app is now type: module;
__dirname via import.meta.url; worker spawned with type module. Preload is built
as CJS (electron-vite output format) because the sandboxed renderer does not
support ESM preload; main loads ../preload/index.js. Removed dead imports
(nativeImage, readline) and the obsolete scripts/dev.js.

Tests: 4 app tests require->import; app-main-settings rewritten with node:test
mock.module + dynamic import (replacing CJS Module._load mocking); test script
adds --experimental-test-module-mocks. electron-vite build clean, 119/119, and
npm run dev verified: app launches, preload bridges IPC, data loads.

app/src/main/index.js

@@ -1,12 +1,16 @@
-const { app, BrowserWindow, ipcMain, clipboard, dialog, nativeImage } = require('electron');
-const path = require('path');
-const os = require('os');
-const fs = require('fs');
-const Database = require('better-sqlite3');
-const { writeHeartbeat } = require('./indexer');
-const { createIndexerService } = require('./indexer-service');
-const { createWorkerBuildIndex } = require('./indexer-worker-client');
-const { buildRecapExportQuery } = require('./recap-capture-query');
+import { app, BrowserWindow, ipcMain, clipboard, dialog, shell } from 'electron';
+import path from 'node:path';
+import os from 'node:os';
+import fs from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import Database from 'better-sqlite3';
+import chokidar from 'chokidar';
+import { writeHeartbeat } from './indexer.js';
+import { createIndexerService } from './indexer-service.js';
+import { createWorkerBuildIndex } from './indexer-worker-client.js';
+import { buildRecapExportQuery } from './recap-capture-query.js';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
 
 function detectClaudeDir() {
   // macOS / Linux: ~/.claude
@@ -283,7 +287,6 @@ let obeliskWatcher = null;
 
 function startObeliskWatcher() {
   if (obeliskWatcher) return obeliskWatcher;
-  const chokidar = require('chokidar');
   if (!fs.existsSync(OBELISK_DIR)) {
     fs.mkdirSync(OBELISK_DIR, { recursive: true });
   }
@@ -488,7 +491,6 @@ ipcMain.handle('db:getMessageFullText', (_, uuid) => {
   if (!jsonlPath || !fs.existsSync(jsonlPath)) return null;
 
   // Scan JSONL for the message UUID and extract full text
-  const readline = require('readline');
   const data = fs.readFileSync(jsonlPath, 'utf-8');
   const lines = data.split('\n');
   for (const line of lines) {
@@ -809,7 +811,6 @@ ipcMain.handle('settings:browseFolder', async (event) => {
 });
 
 ipcMain.handle('settings:revealPath', (_, p) => {
-  const { shell } = require('electron');
   if (fs.existsSync(p)) shell.showItemInFolder(p);
 });
 

app/src/main/indexer-service.js

@@ -1,6 +1,7 @@
-const fs = require('fs');
-const os = require('os');
-const path = require('path');
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import chokidarModule from 'chokidar';
 
 const DEFAULT_PROJECTS_DIR = path.join(os.homedir(), '.claude', 'projects');
 const DEFAULT_DEBOUNCE_MS = 2000;
@@ -38,7 +39,7 @@ function createIndexerService({
       if (!name || name.endsWith('.jsonl') || name.endsWith('.json')) onChange(name);
     };
     for (const root of existingRoots) {
-      const watcher = (chokidar || require('chokidar')).watch(root, {
+      const watcher = (chokidar || chokidarModule).watch(root, {
         cwd: root,
         ignoreInitial: true,
         awaitWriteFinish: {
@@ -192,4 +193,4 @@ function createIndexerService({
   };
 }
 
-module.exports = { createIndexerService };
+export { createIndexerService };

app/src/main/indexer-worker-client.js

@@ -1,5 +1,8 @@
-const path = require('path');
-const { Worker } = require('worker_threads');
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { Worker } from 'node:worker_threads';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
 
 function createWorkerBuildIndex({
   workerPath = path.join(__dirname, 'indexer-worker.js'),
@@ -16,7 +19,7 @@ function createWorkerBuildIndex({
 
   const ensureWorker = () => {
     if (worker) return worker;
-    worker = new WorkerImpl(workerPath);
+    worker = new WorkerImpl(workerPath, { type: 'module' });
     worker.on('message', (message) => {
       const current = pending.get(message.id);
       if (!current) return;
@@ -57,4 +60,4 @@ function createWorkerBuildIndex({
   return { buildIndex, stop };
 }
 
-module.exports = { createWorkerBuildIndex };
+export { createWorkerBuildIndex };

app/src/main/indexer-worker.js

@@ -1,5 +1,5 @@
-const { parentPort } = require('worker_threads');
-const { buildIndex } = require('./indexer');
+import { parentPort } from 'node:worker_threads';
+import { buildIndex } from './indexer.js';
 
 parentPort.on('message', ({ id, args }) => {
   try {

app/src/main/indexer.js

@@ -1,7 +1,10 @@
-const fs = require('fs');
-const os = require('os');
-const path = require('path');
-const Database = require('better-sqlite3');
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import Database from 'better-sqlite3';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
 
 const TEXT_LIMIT = 10000;
 const DEFAULT_CLAUDE_DIR = path.join(os.homedir(), '.claude');
@@ -1161,7 +1164,7 @@ function buildIndex({
   }
 }
 
-module.exports = {
+export {
   buildIndex,
   writeHeartbeat,
   openIndexDb,

app/src/main/recap-capture-query.js

@@ -1,4 +1,4 @@
-const path = require('path');
+import path from 'node:path';
 
 function cleanRecapFilename(filename) {
   if (!filename) return '';
@@ -15,4 +15,4 @@ function buildRecapExportQuery({ cardIdx = 0, archetype = '', filename = '' } =
   return params.toString();
 }
 
-module.exports = { buildRecapExportQuery, cleanRecapFilename };
+export { buildRecapExportQuery, cleanRecapFilename };