diff --git a/app/electron.vite.config.ts b/app/electron.vite.config.ts
index 59c8e42..83f6faa 100644
--- a/app/electron.vite.config.ts
+++ b/app/electron.vite.config.ts
@@ -2,22 +2,22 @@ import { resolve } from 'node:path';
 import { defineConfig, externalizeDepsPlugin } from 'electron-vite';
 import vue from '@vitejs/plugin-vue';
 
-// Kept CommonJS for the first electron-vite boot (no "type":"module" yet); the
-// TS + ESM migration is a later stage. Each main-process module is its own input
-// so it is emitted to out/main/<name>.js and the CommonJS require("./x") calls
-// between them (and `new Worker(__dirname/indexer-worker.js)`) resolve at runtime.
+// The app main/preload/renderer are TypeScript + ESM. Each main-process module
+// is its own rollup input so it is emitted to out/main/<name>.js and the
+// relative imports between them (and `new Worker(__dirname/indexer-worker.js)`)
+// resolve to the built .js at runtime.
 export default defineConfig({
   main: {
     plugins: [externalizeDepsPlugin()],
     build: {
       rollupOptions: {
         input: {
-          index: resolve('src/main/index.js'),
-          indexer: resolve('src/main/indexer.js'),
-          'indexer-service': resolve('src/main/indexer-service.js'),
-          'indexer-worker': resolve('src/main/indexer-worker.js'),
-          'indexer-worker-client': resolve('src/main/indexer-worker-client.js'),
-          'recap-capture-query': resolve('src/main/recap-capture-query.js'),
+          index: resolve('src/main/index.ts'),
+          indexer: resolve('src/main/indexer.ts'),
+          'indexer-service': resolve('src/main/indexer-service.ts'),
+          'indexer-worker': resolve('src/main/indexer-worker.ts'),
+          'indexer-worker-client': resolve('src/main/indexer-worker-client.ts'),
+          'recap-capture-query': resolve('src/main/recap-capture-query.ts'),
         },
       },
     },
diff --git a/app/package-lock.json b/app/package-lock.json
index c297a04..a17f096 100644
--- a/app/package-lock.json
+++ b/app/package-lock.json
@@ -12,6 +12,7 @@
         "chokidar": "^4.0.3"
       },
       "devDependencies": {
+        "@types/better-sqlite3": "^7.6.13",
         "@vitejs/plugin-vue": "^5.0.0",
         "electron": "^33.0.0",
         "electron-builder": "^25.0.0",
@@ -1848,6 +1849,16 @@
         "node": ">= 10"
       }
     },
+    "node_modules/@types/better-sqlite3": {
+      "version": "7.6.13",
+      "resolved": "https://registry.npmjs.org/@types/better-sqlite3/-/better-sqlite3-7.6.13.tgz",
+      "integrity": "sha512-NMv9ASNARoKksWtsq/SHakpYAYnhBrQgGD8zkLYk/jaK8jUGn08CfEdTRgYhMypUQAfzSP8W6gNLe0q19/t4VA==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/node": "*"
+      }
+    },
     "node_modules/@types/cacheable-request": {
       "version": "6.0.3",
       "resolved": "https://registry.npmjs.org/@types/cacheable-request/-/cacheable-request-6.0.3.tgz",
diff --git a/app/package.json b/app/package.json
index 790c354..49e9a16 100644
--- a/app/package.json
+++ b/app/package.json
@@ -60,6 +60,7 @@
     "chokidar": "^4.0.3"
   },
   "devDependencies": {
+    "@types/better-sqlite3": "^7.6.13",
     "@vitejs/plugin-vue": "^5.0.0",
     "electron": "^33.0.0",
     "electron-builder": "^25.0.0",
diff --git a/app/src/main/index.js b/app/src/main/index.ts
similarity index 97%
rename from app/src/main/index.js
rename to app/src/main/index.ts
index 88f1700..ebdb5fb 100644
--- a/app/src/main/index.js
+++ b/app/src/main/index.ts
@@ -5,10 +5,10 @@ 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';
+import { writeHeartbeat } from './indexer.ts';
+import { createIndexerService } from './indexer-service.ts';
+import { createWorkerBuildIndex } from './indexer-worker-client.ts';
+import { buildRecapExportQuery } from './recap-capture-query.ts';
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
 
@@ -68,7 +68,7 @@ function migrateLegacyDbIfNeeded(paths = getPathsForClaudeDir()) {
     fs.mkdirSync(path.dirname(paths.dbPath), { recursive: true });
     fs.copyFileSync(legacyDbPath, paths.dbPath);
   } catch (error) {
-    console.warn?.(`Obelisk legacy DB migration skipped: ${error.message}`);
+    console.warn?.(`Obelisk legacy DB migration skipped: ${(error as Error).message}`);
   }
 }
 
@@ -111,7 +111,7 @@ function resolveSchemaPath() {
     path.join(__dirname, 'schema.sql'),
     path.join(__dirname, '..', 'scripts', 'schema.sql'),
     process.resourcesPath ? path.join(process.resourcesPath, 'scripts', 'schema.sql') : null,
-  ].filter(Boolean);
+  ].filter((c): c is string => Boolean(c));
   return candidates.find(p => fs.existsSync(p));
 }
 
@@ -160,7 +160,7 @@ function openDb(dbPath = getPathsForClaudeDir().dbPath) {
   return db;
 }
 
-function notifyIndexUpdated(result = {}) {
+function notifyIndexUpdated(result: { affectedSessionIds?: unknown } = {}) {
   const affectedSessionIds = Array.isArray(result.affectedSessionIds)
     ? [...new Set(result.affectedSessionIds.filter(Boolean))]
     : [];
@@ -173,7 +173,7 @@ function notifyIndexUpdated(result = {}) {
   }
 }
 
-function sourceWhereClause(opts = {}, column = 'source') {
+function sourceWhereClause(opts: { includeCodex?: boolean; source?: string } = {}, column = "source"): { sql: string; params: unknown[] } {
   if (opts.includeCodex || opts.source === 'all') return { sql: '', params: [] };
   if (opts.source) return { sql: `COALESCE(${column}, 'claude') = ?`, params: [opts.source] };
   return { sql: `COALESCE(${column}, 'claude') = 'claude'`, params: [] };
@@ -283,7 +283,7 @@ function createWindow() {
 
 const OBELISK_DIR = path.join(os.homedir(), '.obelisk');
 const RECAP_DIR = path.join(OBELISK_DIR, 'recap');
-let obeliskWatcher = null;
+let obeliskWatcher: import("chokidar").FSWatcher | null = null;
 
 function startObeliskWatcher() {
   if (obeliskWatcher) return obeliskWatcher;
@@ -340,7 +340,7 @@ ipcMain.handle('db:getSessions', (_, opts = {}) => {
   if (!db) return [];
   const { project, limit = 200 } = opts;
   let sql = `SELECT id, title, project, project_path, started_at, ended_at, git_branch, version, message_count, jsonl_path, source FROM sessions`;
-  const params = [];
+  const params: unknown[] = [];
   const sourceFilter = sourceWhereClause(opts);
   if (sourceFilter.sql) {
     sql = appendWhere(sql, params, sourceFilter.sql);
@@ -437,7 +437,7 @@ ipcMain.handle('db:getMessageFullText', (_, uuid) => {
     if (!match) return null;
     const rawThreadId = match[1];
     const targetLine = Number(match[2]);
-    let jsonlPath = null;
+    let jsonlPath: string | null = null;
     if (!msg.agent_id) {
       jsonlPath = db.prepare('SELECT jsonl_path FROM sessions WHERE id=?').get(msg.session_id)?.jsonl_path || null;
     }
@@ -469,7 +469,7 @@ ipcMain.handle('db:getMessageFullText', (_, uuid) => {
   }
 
   // Resolve JSONL path
-  let jsonlPath = null;
+  let jsonlPath: string | null = null;
   if (msg.agent_id) {
     const wa = db.prepare('SELECT agent_id, run_id, session_id FROM workflow_agents WHERE agent_id=?').get(msg.agent_id);
     if (wa) {
@@ -501,7 +501,7 @@ ipcMain.handle('db:getMessageFullText', (_, uuid) => {
       const content = obj.message?.content;
       if (typeof content === 'string') return content;
       if (!Array.isArray(content)) return null;
-      const parts = [];
+      const parts: string[] = [];
       for (const b of content) {
         if (b.type === 'text' && b.text) parts.push(b.text);
         else if (b.type === 'thinking' && b.thinking) parts.push(b.thinking);
@@ -614,7 +614,7 @@ async function createExportCapture(parentWin, query) {
       nodeIntegration: false,
       offscreen: true,
       deviceScaleFactor: 2,
-    },
+    } as Electron.WebPreferences,
   });
 
   const isDev = process.argv.includes('--dev') || !!process.env.ELECTRON_RENDERER_URL;
@@ -802,6 +802,7 @@ ipcMain.handle('settings:set', async (_, key, value) => {
 
 ipcMain.handle('settings:browseFolder', async (event) => {
   const win = BrowserWindow.fromWebContents(event.sender);
+  if (!win) return null;
   const { filePaths } = await dialog.showOpenDialog(win, {
     properties: ['openDirectory'],
     title: 'Select Claude Code data folder',
@@ -851,7 +852,7 @@ ipcMain.handle('settings:rebuildIndex', async () => {
       try {
         openDb(paths.dbPath);
       } catch (error) {
-        console.warn?.(`Obelisk DB reopen after rebuild failed: ${error.message}`);
+        console.warn?.(`Obelisk DB reopen after rebuild failed: ${(error as Error).message}`);
       }
     }
     if (shouldRestartWatcher) startIndexerService({ buildOnStart: false });
diff --git a/app/src/main/indexer-service.js b/app/src/main/indexer-service.ts
similarity index 76%
rename from app/src/main/indexer-service.js
rename to app/src/main/indexer-service.ts
index 0b63fe3..407b310 100644
--- a/app/src/main/indexer-service.js
+++ b/app/src/main/indexer-service.ts
@@ -9,6 +9,34 @@ const DEFAULT_STABILITY_MS = 500;
 const DEFAULT_HEARTBEAT_MS = 30000;
 const DEFAULT_WATCH_RETRY_MS = 5000;
 
+type TimerHandle = ReturnType<typeof setTimeout>;
+
+interface Timers {
+  setTimeout: (fn: () => void, ms?: number) => TimerHandle;
+  clearTimeout: (handle: TimerHandle) => void;
+  setInterval?: (fn: () => void, ms?: number) => TimerHandle;
+  clearInterval?: (handle: TimerHandle) => void;
+}
+
+interface Watcher {
+  close(): unknown;
+}
+
+interface IndexerServiceOptions {
+  projectsDir?: string;
+  watchDirs?: string | string[];
+  debounceMs?: number;
+  stabilityMs?: number;
+  heartbeatMs?: number;
+  watchRetryMs?: number;
+  buildIndex?: (args: { reason?: string; changedPaths?: string[] }) => unknown;
+  writeHeartbeat?: () => void;
+  watchProjects?: (onChange: (changedPath: string) => void) => Watcher | null;
+  chokidar?: any;
+  timers?: Timers;
+  logger?: { warn?: (msg: string) => void };
+}
+
 function createIndexerService({
   projectsDir = DEFAULT_PROJECTS_DIR,
   watchDirs = [projectsDir],
@@ -27,13 +55,13 @@ function createIndexerService({
     clearInterval,
   },
   logger = console,
-} = {}) {
+}: IndexerServiceOptions = {}) {
   if (typeof buildIndex !== 'function') throw new Error('createIndexerService() requires buildIndex');
   const watch = watchProjects || ((onChange) => {
     const roots = [...new Set((Array.isArray(watchDirs) ? watchDirs : [watchDirs]).filter(Boolean))];
     const existingRoots = roots.filter(root => fs.existsSync(root));
     if (!existingRoots.length) return null;
-    const watchers = [];
+    const watchers: any[] = [];
     const onFileChange = (filename) => {
       const name = filename ? String(filename) : '';
       if (!name || name.endsWith('.jsonl') || name.endsWith('.json')) onChange(name);
@@ -57,7 +85,7 @@ function createIndexerService({
         .on('change', onFileChange)
         .on('unlink', onFileChange)
         .on('error', (error) => {
-          logger.warn?.(`Obelisk watcher failed: ${error.message}`);
+          logger.warn?.(`Obelisk watcher failed: ${(error as Error).message}`);
         });
       watchers.push(watcher);
     }
@@ -68,19 +96,19 @@ function createIndexerService({
     };
   });
 
-  let buildTimer = null;
-  let stabilityTimer = null;
-  let heartbeatTimer = null;
-  let watchRetryTimer = null;
-  let watcher = null;
+  let buildTimer: TimerHandle | null = null;
+  let stabilityTimer: TimerHandle | null = null;
+  let heartbeatTimer: TimerHandle | null = null;
+  let watchRetryTimer: TimerHandle | null = null;
+  let watcher: Watcher | null = null;
   let stopped = false;
   let running = false;
   let pending = false;
-  let lastReason = null;
-  let changedPaths = new Set();
+  let lastReason: string | null = null;
+  let changedPaths = new Set<string>();
   let idlePromise = Promise.resolve();
 
-  const addChangedPath = (changedPath) => {
+  const addChangedPath = (changedPath?: string | string[]) => {
     if (Array.isArray(changedPath)) {
       for (const p of changedPath) addChangedPath(p);
       return;
@@ -96,7 +124,7 @@ function createIndexerService({
     return paths;
   };
 
-  const runBuildNow = (reason = 'manual', paths = undefined) => {
+  const runBuildNow = (reason = "manual", paths: string[] | undefined = undefined) => {
     addChangedPath(paths);
     if (stopped) return idlePromise;
     if (running) {
@@ -113,7 +141,7 @@ function createIndexerService({
       .catch((error) => {
         // A build in flight when the service is stopped (e.g. a manual rebuild
         // tears down the worker) is a deliberate cancellation, not a failure.
-        if (!stopped) logger.warn?.(`Obelisk index build failed: ${error.message}`);
+        if (!stopped) logger.warn?.(`Obelisk index build failed: ${(error as Error).message}`);
       })
       .finally(() => {
         running = false;
@@ -125,7 +153,7 @@ function createIndexerService({
     return idlePromise;
   };
 
-  const scheduleBuild = (reason = 'change', changedPath = undefined) => {
+  const scheduleBuild = (reason = "change", changedPath: string | undefined = undefined) => {
     if (stopped) return;
     addChangedPath(changedPath);
     lastReason = reason;
@@ -165,7 +193,7 @@ function createIndexerService({
         try {
           writeHeartbeat();
         } catch (error) {
-          logger.warn?.(`Obelisk heartbeat failed: ${error.message}`);
+          logger.warn?.(`Obelisk heartbeat failed: ${(error as Error).message}`);
         }
       }, heartbeatMs);
     }
diff --git a/app/src/main/indexer-worker-client.js b/app/src/main/indexer-worker-client.ts
similarity index 59%
rename from app/src/main/indexer-worker-client.js
rename to app/src/main/indexer-worker-client.ts
index 989312f..5653558 100644
--- a/app/src/main/indexer-worker-client.js
+++ b/app/src/main/indexer-worker-client.ts
@@ -4,23 +4,41 @@ import { Worker } from 'node:worker_threads';
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
 
+interface WorkerMessage {
+  id: number;
+  result?: unknown;
+  error?: { message: string; stack?: string };
+}
+
+interface PendingBuild {
+  resolve: (value: unknown) => void;
+  reject: (error: Error) => void;
+}
+
+interface WorkerBuildIndexOptions {
+  workerPath?: string;
+  WorkerImpl?: typeof Worker;
+}
+
 function createWorkerBuildIndex({
+  // indexer-worker.js is the built worker output emitted next to this module.
   workerPath = path.join(__dirname, 'indexer-worker.js'),
   WorkerImpl = Worker,
-} = {}) {
-  let worker = null;
+}: WorkerBuildIndexOptions = {}) {
+  let worker: Worker | null = null;
   let nextId = 1;
-  const pending = new Map();
+  const pending = new Map<number, PendingBuild>();
 
-  const rejectPending = (error) => {
+  const rejectPending = (error: Error) => {
     for (const { reject } of pending.values()) reject(error);
     pending.clear();
   };
 
-  const ensureWorker = () => {
+  const ensureWorker = (): Worker => {
     if (worker) return worker;
-    worker = new WorkerImpl(workerPath, { type: 'module' });
-    worker.on('message', (message) => {
+    const active = new WorkerImpl(workerPath, { type: 'module' } as ConstructorParameters<typeof Worker>[1]);
+    worker = active;
+    active.on('message', (message: WorkerMessage) => {
       const current = pending.get(message.id);
       if (!current) return;
       pending.delete(message.id);
@@ -32,18 +50,18 @@ function createWorkerBuildIndex({
         current.resolve(message.result);
       }
     });
-    worker.on('error', (error) => {
+    active.on('error', (error: Error) => {
       rejectPending(error);
       worker = null;
     });
-    worker.on('exit', (code) => {
+    active.on('exit', (code: number) => {
       if (pending.size) rejectPending(new Error(`Indexer worker exited with code ${code}`));
       worker = null;
     });
-    return worker;
+    return active;
   };
 
-  const buildIndex = (args = {}) => new Promise((resolve, reject) => {
+  const buildIndex = (args: Record<string, unknown> = {}) => new Promise((resolve, reject) => {
     const id = nextId++;
     pending.set(id, { resolve, reject });
     ensureWorker().postMessage({ id, args });
diff --git a/app/src/main/indexer-worker.js b/app/src/main/indexer-worker.js
deleted file mode 100644
index 2650dc0..0000000
--- a/app/src/main/indexer-worker.js
+++ /dev/null
@@ -1,17 +0,0 @@
-import { parentPort } from 'node:worker_threads';
-import { buildIndex } from './indexer.js';
-
-parentPort.on('message', ({ id, args }) => {
-  try {
-    const result = buildIndex(args || {});
-    parentPort.postMessage({ id, result });
-  } catch (error) {
-    parentPort.postMessage({
-      id,
-      error: {
-        message: error.message,
-        stack: error.stack,
-      },
-    });
-  }
-});
diff --git a/app/src/main/indexer-worker.ts b/app/src/main/indexer-worker.ts
new file mode 100644
index 0000000..7055afa
--- /dev/null
+++ b/app/src/main/indexer-worker.ts
@@ -0,0 +1,20 @@
+import { parentPort } from 'node:worker_threads';
+import { buildIndex } from './indexer.ts';
+
+if (!parentPort) throw new Error('indexer-worker must run as a worker thread');
+const port = parentPort;
+
+port.on('message', ({ id, args }: { id: number; args?: Record<string, unknown> }) => {
+  try {
+    const result = buildIndex(args || {});
+    port.postMessage({ id, result });
+  } catch (error) {
+    port.postMessage({
+      id,
+      error: {
+        message: error instanceof Error ? error.message : String(error),
+        stack: error instanceof Error ? error.stack : undefined,
+      },
+    });
+  }
+});
diff --git a/app/src/main/indexer.js b/app/src/main/indexer.ts
similarity index 91%
rename from app/src/main/indexer.js
rename to app/src/main/indexer.ts
index 8c92e77..fed07f1 100644
--- a/app/src/main/indexer.js
+++ b/app/src/main/indexer.ts
@@ -25,12 +25,22 @@ const DEFAULT_DB_PATH = path.join(DEFAULT_OBELISK_DIR, 'obelisk.sqlite');
 const DEFAULT_PROJECTS_DIR = path.join(DEFAULT_CLAUDE_DIR, 'projects');
 const DEFAULT_HISTORY_PATH = path.join(DEFAULT_CLAUDE_DIR, 'history.jsonl');
 
+interface FileInfo {
+  path: string;
+  sessionId?: string;
+  project?: string;
+  isSubagent?: boolean;
+  agentId?: string;
+  workflowRunId?: string;
+  source?: string;
+}
+
 function resolveSchemaPath() {
   const candidates = [
     path.join(__dirname, 'schema.sql'),
     path.join(__dirname, '..', '..', '..', 'scripts', 'schema.sql'),
     process.resourcesPath ? path.join(process.resourcesPath, 'scripts', 'schema.sql') : null,
-  ].filter(Boolean);
+  ].filter((c): c is string => Boolean(c));
   const found = candidates.find(p => fs.existsSync(p));
   if (!found) throw new Error('Obelisk schema.sql not found');
   return found;
@@ -41,7 +51,7 @@ function installSchema(db, schemaPath = resolveSchemaPath()) {
   migrateDb(db);
 }
 
-function openIndexDb({ dbPath = DEFAULT_DB_PATH, schemaPath = resolveSchemaPath(), DatabaseImpl = Database } = {}) {
+function openIndexDb({ dbPath = DEFAULT_DB_PATH, schemaPath = resolveSchemaPath(), DatabaseImpl = Database }: { dbPath?: string; schemaPath?: string; DatabaseImpl?: new (dbPath: string) => any } = {}) {
   fs.mkdirSync(path.dirname(dbPath), { recursive: true });
   const db = new DatabaseImpl(dbPath);
   db.pragma('journal_mode = WAL');
@@ -104,7 +114,7 @@ function copyMemoriesFromDb(db, sourceDbPath) {
   }
 }
 
-function discoverJsonlFiles({ projectsDir = DEFAULT_PROJECTS_DIR, changedPaths = undefined } = {}) {
+function discoverJsonlFiles({ projectsDir = DEFAULT_PROJECTS_DIR, changedPaths = undefined }: { projectsDir?: string; changedPaths?: string[] } = {}) {
   if (Array.isArray(changedPaths) && changedPaths.length) {
     const changedFiles = discoverJsonlFilesForChanges({ projectsDir, changedPaths });
     if (changedFiles.length) return changedFiles;
@@ -168,8 +178,8 @@ function dedupeFileInfos(files) {
   return [...byPath.values()];
 }
 
-function discoverJsonlFilesForChanges({ projectsDir = DEFAULT_PROJECTS_DIR, changedPaths = [] } = {}) {
-  const files = [];
+function discoverJsonlFilesForChanges({ projectsDir = DEFAULT_PROJECTS_DIR, changedPaths = [] }: { projectsDir?: string; changedPaths?: string[] } = {}) {
+  const files: FileInfo[] = [];
   for (const changedPath of changedPaths) {
     const info = jsonlFileInfoFromPath(projectsDir, changedPath);
     if (info) files.push(info);
@@ -178,7 +188,7 @@ function discoverJsonlFilesForChanges({ projectsDir = DEFAULT_PROJECTS_DIR, chan
 }
 
 function discoverJsonlFilesFull({ projectsDir = DEFAULT_PROJECTS_DIR } = {}) {
-  const files = [];
+  const files: FileInfo[] = [];
   if (!fs.existsSync(projectsDir)) return files;
   let projects;
   try { projects = fs.readdirSync(projectsDir); } catch { return files; }
@@ -219,7 +229,7 @@ function discoverJsonlFilesFull({ projectsDir = DEFAULT_PROJECTS_DIR } = {}) {
   return files;
 }
 
-function discoverCodexJsonlFiles({ codexDir = DEFAULT_CODEX_DIR, changedPaths = undefined } = {}) {
+function discoverCodexJsonlFiles({ codexDir = DEFAULT_CODEX_DIR, changedPaths = undefined }: { codexDir?: string; changedPaths?: string[] } = {}) {
   if (Array.isArray(changedPaths) && changedPaths.length) {
     const changedFiles = discoverCodexJsonlFilesForChanges({ codexDir, changedPaths });
     if (changedFiles.length) return changedFiles;
@@ -244,8 +254,8 @@ function isPathInside(rootDir, candidate) {
   return !!rel && !rel.startsWith('..') && !path.isAbsolute(rel);
 }
 
-function discoverCodexJsonlFilesForChanges({ codexDir = DEFAULT_CODEX_DIR, changedPaths = [] } = {}) {
-  const files = [];
+function discoverCodexJsonlFilesForChanges({ codexDir = DEFAULT_CODEX_DIR, changedPaths = [] }: { codexDir?: string; changedPaths?: string[] } = {}) {
+  const files: FileInfo[] = [];
   const sessionsDir = codexSessionsDir(codexDir);
   for (const changedPath of changedPaths) {
     const rootRelativePath = normalizeChangedPathForRoot(codexDir, changedPath);
@@ -255,7 +265,7 @@ function discoverCodexJsonlFilesForChanges({ codexDir = DEFAULT_CODEX_DIR, chang
     }
     const sessionRelativePath = normalizeChangedPathForRoot(sessionsDir, changedPath);
     const fp = isPathInside(sessionsDir, rootRelativePath) ? rootRelativePath : sessionRelativePath;
-    if (!fp.endsWith('.jsonl') || !isPathInside(sessionsDir, fp)) continue;
+    if (!fp || !fp.endsWith(".jsonl") || !isPathInside(sessionsDir, fp)) continue;
     if (!fs.existsSync(fp)) continue;
     files.push({ path: fp, source: 'codex' });
   }
@@ -264,11 +274,11 @@ function discoverCodexJsonlFilesForChanges({ codexDir = DEFAULT_CODEX_DIR, chang
 
 function discoverCodexJsonlFilesFull({ codexDir = DEFAULT_CODEX_DIR } = {}) {
   const root = codexSessionsDir(codexDir);
-  const files = [];
+  const files: FileInfo[] = [];
   if (!fs.existsSync(root)) return files;
   const stack = [root];
   while (stack.length) {
-    const current = stack.pop();
+    const current = stack.pop()!;
     let entries;
     try { entries = fs.readdirSync(current, { withFileTypes: true }); } catch { continue; }
     for (const entry of entries) {
@@ -308,7 +318,7 @@ function indexClaudeFile(db, file) {
 }
 
 function codexSessionMeta(filePath) {
-  let meta = null;
+  let meta: any = null;
   readLines(filePath, (line) => {
     let obj;
     try { obj = JSON.parse(line); } catch { return; }
@@ -328,7 +338,7 @@ function indexCodexFile(db, file) {
   if (!needed) {
     if (guardian) {
       persist(db, { key: file.path, sessionId: '' }, (function* () {
-        yield { kind: 'delete-session', sessionId: codexDbId(guardian.threadRawId) };
+        yield { kind: "delete-session", sessionId: codexDbId(guardian.threadRawId) as string };
         return null;
       })());
     }
@@ -352,7 +362,7 @@ function indexCodexSessionIndex(db, { codexDir = DEFAULT_CODEX_DIR } = {}) {
       db.prepare('UPDATE sessions SET title=COALESCE(title, ?), ended_at=COALESCE(ended_at, ?) WHERE id=? AND source=?')
         .run(item.thread_name, item.updated_at || null, codexDbId(item.id), 'codex');
     } catch (error) {
-      console.warn(`Warning: malformed Codex session index line: ${error.message}`);
+      console.warn(`Warning: malformed Codex session index line: ${(error as Error).message}`);
     }
   });
 }
@@ -387,7 +397,7 @@ function indexSubagentMeta(db, fi) {
       db.prepare('INSERT OR REPLACE INTO subagents VALUES(?,?,?,?,?,?,?)').run(fi.agentId, fi.sessionId, meta.toolUseId||null, meta.agentType||null, meta.description||null, dur, tok?.t||0);
     }
   } catch (error) {
-    console.warn(`Warning: failed to read subagent meta ${mp}: ${error.message}`);
+    console.warn(`Warning: failed to read subagent meta ${mp}: ${(error as Error).message}`);
   }
 }
 
@@ -423,7 +433,7 @@ function indexWorkflows(db, { projectsDir = DEFAULT_PROJECTS_DIR } = {}) {
               item.durationMs||null, item.tokens||null, item.toolCalls||null, 'agent-' + item.agentId);
           }
         } catch (error) {
-          console.warn(`Warning: failed to index workflow ${f}: ${error.message}`);
+          console.warn(`Warning: failed to index workflow ${f}: ${(error as Error).message}`);
         }
       }
     }
@@ -437,7 +447,7 @@ function indexHistory(db, { historyPath = DEFAULT_HISTORY_PATH } = {}) {
       const o = JSON.parse(line);
       if (o.sessionId && o.title) db.prepare('UPDATE sessions SET title=? WHERE id=? AND title IS NULL').run(o.title, o.sessionId);
     } catch (error) {
-      console.warn(`Warning: malformed history line: ${error.message}`);
+      console.warn(`Warning: malformed history line: ${(error as Error).message}`);
     }
   });
 }
@@ -488,6 +498,26 @@ function writeHeartbeat({ dbPath = DEFAULT_DB_PATH, DatabaseImpl = Database } =
   }
 }
 
+interface BuildIndexOptions {
+  claudeDir?: string;
+  codexDir?: string;
+  projectsDir?: string;
+  historyPath?: string;
+  dbPath?: string;
+  schemaPath?: string;
+  DatabaseImpl?: new (dbPath: string) => any;
+  force?: boolean;
+  changedPaths?: string[];
+  preserveDbPath?: string | null;
+}
+
+interface BuildIndexResult {
+  files: number;
+  latestSourceMtime: number;
+  affectedSessionIds: string[];
+  ftsRebuilt: boolean;
+}
+
 function buildIndex({
   claudeDir = DEFAULT_CLAUDE_DIR,
   codexDir = path.join(path.dirname(claudeDir), '.codex'),
@@ -499,7 +529,7 @@ function buildIndex({
   force = false,
   changedPaths = undefined,
   preserveDbPath = null,
-} = {}) {
+}: BuildIndexOptions = {}): BuildIndexResult {
   const db = openIndexDb({ dbPath, schemaPath, DatabaseImpl });
   let messageFtsTriggersDropped = false;
   if (preserveDbPath && path.resolve(preserveDbPath) !== path.resolve(dbPath)) {
@@ -531,7 +561,7 @@ function buildIndex({
       db.prepare("DELETE FROM workflows").run();
       db.prepare("DELETE FROM workflow_agents").run();
     }
-    const affectedSessionIds = new Set();
+    const affectedSessionIds = new Set<string>();
     if (Array.isArray(changedPaths)) {
       for (const changedPath of changedPaths) {
         const sessionId = sessionIdFromChangedPath(projectsDir, changedPath);
@@ -547,7 +577,7 @@ function buildIndex({
         db.exec('COMMIT');
       } catch (error) {
         db.exec('ROLLBACK');
-        console.warn(`Warning: failed to index ${file.path}: ${error.message}`);
+        console.warn(`Warning: failed to index ${file.path}: ${(error as Error).message}`);
       }
     }
     db.exec('BEGIN');
@@ -575,7 +605,7 @@ function buildIndex({
       try {
         installSchema(db, schemaPath);
       } catch (error) {
-        console.warn(`Warning: failed to restore message FTS triggers: ${error.message}`);
+        console.warn(`Warning: failed to restore message FTS triggers: ${(error as Error).message}`);
       }
     }
     checkpointDb(db);
diff --git a/app/src/main/recap-capture-query.js b/app/src/main/recap-capture-query.ts
similarity index 71%
rename from app/src/main/recap-capture-query.js
rename to app/src/main/recap-capture-query.ts
index 4e037c4..70a4d3c 100644
--- a/app/src/main/recap-capture-query.js
+++ b/app/src/main/recap-capture-query.ts
@@ -1,11 +1,17 @@
 import path from 'node:path';
 
-function cleanRecapFilename(filename) {
+function cleanRecapFilename(filename?: string | null): string {
   if (!filename) return '';
   return path.basename(String(filename));
 }
 
-function buildRecapExportQuery({ cardIdx = 0, archetype = '', filename = '' } = {}) {
+interface RecapExportQueryOptions {
+  cardIdx?: number | string;
+  archetype?: string;
+  filename?: string;
+}
+
+function buildRecapExportQuery({ cardIdx = 0, archetype = '', filename = '' }: RecapExportQueryOptions = {}): string {
   const params = new URLSearchParams();
   const cardNumber = Number(cardIdx);
   params.set('card', Number.isFinite(cardNumber) ? String(cardNumber) : '0');
diff --git a/app/src/preload/index.js b/app/src/preload/index.js
deleted file mode 100644
index c03fcd5..0000000
--- a/app/src/preload/index.js
+++ /dev/null
@@ -1,46 +0,0 @@
-import { contextBridge, ipcRenderer } from 'electron';
-
-contextBridge.exposeInMainWorld('obelisk', {
-  getSessions: (opts) => ipcRenderer.invoke('db:getSessions', opts),
-  getSessionMessages: (id) => ipcRenderer.invoke('db:getSessionMessages', id),
-  getSessionToolCalls: (id) => ipcRenderer.invoke('db:getSessionToolCalls', id),
-  getSessionToolResults: (id) => ipcRenderer.invoke('db:getSessionToolResults', id),
-  getSessionSubagents: (id) => ipcRenderer.invoke('db:getSessionSubagents', id),
-  getSessionWorkflows: (id) => ipcRenderer.invoke('db:getSessionWorkflows', id),
-  getSubagentMessages: (agentId) => ipcRenderer.invoke('db:getSubagentMessages', agentId),
-  getSubagentToolCalls: (agentId) => ipcRenderer.invoke('db:getSubagentToolCalls', agentId),
-  getSubagentToolResults: (agentId) => ipcRenderer.invoke('db:getSubagentToolResults', agentId),
-  getSessionSummaries: (id) => ipcRenderer.invoke('db:getSessionSummaries', id),
-  getMessageFullText: (uuid) => ipcRenderer.invoke('db:getMessageFullText', uuid),
-  getMemories: () => ipcRenderer.invoke('db:getMemories'),
-  readMemoryFile: (path) => ipcRenderer.invoke('db:readMemoryFile', path),
-  archiveMemory: (id, reason) => ipcRenderer.invoke('db:archiveMemory', id, reason),
-  restoreMemory: (id) => ipcRenderer.invoke('db:restoreMemory', id),
-  getProjects: () => ipcRenderer.invoke('db:getProjects'),
-  getStats: () => ipcRenderer.invoke('db:getStats'),
-  getUsageStats: () => ipcRenderer.invoke('db:getUsageStats'),
-  onIndexUpdated: (callback) => {
-    const listener = (_, payload) => callback(payload);
-    ipcRenderer.on('obelisk:index-updated', listener);
-    return () => ipcRenderer.removeListener('obelisk:index-updated', listener);
-  },
-  onSessionUpdated: (callback) => {
-    const listener = (_, payload) => callback(payload);
-    ipcRenderer.on('obelisk:session-updated', listener);
-    return () => ipcRenderer.removeListener('obelisk:session-updated', listener);
-  },
-  captureExport: (opts) => ipcRenderer.invoke('capture:export', opts),
-  copyImage: (opts) => ipcRenderer.invoke('capture:copy', opts),
-  recapList: () => ipcRenderer.invoke('recap:list'),
-  recapRead: (filename) => ipcRenderer.invoke('recap:read', filename),
-  onRecapUpdated: (callback) => {
-    const listener = (_, filePath) => callback(filePath);
-    ipcRenderer.on('obelisk:recap-updated', listener);
-    return () => ipcRenderer.removeListener('obelisk:recap-updated', listener);
-  },
-  getSettings: () => ipcRenderer.invoke('settings:get'),
-  browseFolder: () => ipcRenderer.invoke('settings:browseFolder'),
-  setSetting: (key, value) => ipcRenderer.invoke('settings:set', key, value),
-  revealPath: (p) => ipcRenderer.invoke('settings:revealPath', p),
-  rebuildIndex: () => ipcRenderer.invoke('settings:rebuildIndex'),
-});
diff --git a/app/src/preload/index.ts b/app/src/preload/index.ts
new file mode 100644
index 0000000..5308f25
--- /dev/null
+++ b/app/src/preload/index.ts
@@ -0,0 +1,46 @@
+import { contextBridge, ipcRenderer, type IpcRendererEvent } from 'electron';
+
+contextBridge.exposeInMainWorld('obelisk', {
+  getSessions: (opts?: unknown) => ipcRenderer.invoke('db:getSessions', opts),
+  getSessionMessages: (id: string) => ipcRenderer.invoke('db:getSessionMessages', id),
+  getSessionToolCalls: (id: string) => ipcRenderer.invoke('db:getSessionToolCalls', id),
+  getSessionToolResults: (id: string) => ipcRenderer.invoke('db:getSessionToolResults', id),
+  getSessionSubagents: (id: string) => ipcRenderer.invoke('db:getSessionSubagents', id),
+  getSessionWorkflows: (id: string) => ipcRenderer.invoke('db:getSessionWorkflows', id),
+  getSubagentMessages: (agentId: string) => ipcRenderer.invoke('db:getSubagentMessages', agentId),
+  getSubagentToolCalls: (agentId: string) => ipcRenderer.invoke('db:getSubagentToolCalls', agentId),
+  getSubagentToolResults: (agentId: string) => ipcRenderer.invoke('db:getSubagentToolResults', agentId),
+  getSessionSummaries: (id: string) => ipcRenderer.invoke('db:getSessionSummaries', id),
+  getMessageFullText: (uuid: string) => ipcRenderer.invoke('db:getMessageFullText', uuid),
+  getMemories: () => ipcRenderer.invoke('db:getMemories'),
+  readMemoryFile: (path: string) => ipcRenderer.invoke('db:readMemoryFile', path),
+  archiveMemory: (id: string, reason?: string) => ipcRenderer.invoke('db:archiveMemory', id, reason),
+  restoreMemory: (id: string) => ipcRenderer.invoke('db:restoreMemory', id),
+  getProjects: () => ipcRenderer.invoke('db:getProjects'),
+  getStats: () => ipcRenderer.invoke('db:getStats'),
+  getUsageStats: () => ipcRenderer.invoke('db:getUsageStats'),
+  onIndexUpdated: (callback: (payload: unknown) => void) => {
+    const listener = (_: IpcRendererEvent, payload: unknown) => callback(payload);
+    ipcRenderer.on('obelisk:index-updated', listener);
+    return () => ipcRenderer.removeListener('obelisk:index-updated', listener);
+  },
+  onSessionUpdated: (callback: (payload: unknown) => void) => {
+    const listener = (_: IpcRendererEvent, payload: unknown) => callback(payload);
+    ipcRenderer.on('obelisk:session-updated', listener);
+    return () => ipcRenderer.removeListener('obelisk:session-updated', listener);
+  },
+  captureExport: (opts?: unknown) => ipcRenderer.invoke('capture:export', opts),
+  copyImage: (opts?: unknown) => ipcRenderer.invoke('capture:copy', opts),
+  recapList: () => ipcRenderer.invoke('recap:list'),
+  recapRead: (filename: string) => ipcRenderer.invoke('recap:read', filename),
+  onRecapUpdated: (callback: (filePath: unknown) => void) => {
+    const listener = (_: IpcRendererEvent, filePath: unknown) => callback(filePath);
+    ipcRenderer.on('obelisk:recap-updated', listener);
+    return () => ipcRenderer.removeListener('obelisk:recap-updated', listener);
+  },
+  getSettings: () => ipcRenderer.invoke('settings:get'),
+  browseFolder: () => ipcRenderer.invoke('settings:browseFolder'),
+  setSetting: (key: string, value: unknown) => ipcRenderer.invoke('settings:set', key, value),
+  revealPath: (p: string) => ipcRenderer.invoke('settings:revealPath', p),
+  rebuildIndex: () => ipcRenderer.invoke('settings:rebuildIndex'),
+});
diff --git a/app/tsconfig.json b/app/tsconfig.json
new file mode 100644
index 0000000..5d183db
--- /dev/null
+++ b/app/tsconfig.json
@@ -0,0 +1,22 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "lib": ["ES2023"],
+    "types": ["node"],
+    "strict": true,
+    "noImplicitAny": false,
+    "noEmit": true,
+    "allowImportingTsExtensions": true,
+    "allowJs": true,
+    "checkJs": false,
+    "erasableSyntaxOnly": true,
+    "skipLibCheck": true,
+    "esModuleInterop": true,
+    "resolveJsonModule": true,
+    "forceConsistentCasingInFileNames": true
+  },
+  "include": ["src/main/**/*", "src/preload/**/*"],
+  "exclude": ["node_modules", "out", "dist", "release", "src/renderer"]
+}
diff --git a/docs/adr/0005-app-electron-vite-ts-esm.md b/docs/adr/0005-app-electron-vite-ts-esm.md
index 5484d15..8a6bfcb 100644
--- a/docs/adr/0005-app-electron-vite-ts-esm.md
+++ b/docs/adr/0005-app-electron-vite-ts-esm.md
@@ -27,11 +27,32 @@ decisions within this:
   (ADR-0003) remains for the skill artifact; the app does not need it.
 - **better-sqlite3 stays the app's binding**, externalized (not bundled) and
   unpacked from the asar.
+- **The app main + preload source is TypeScript with types at its seams**, but
+  under a *deliberately more lenient* project than the runtime core. `app/tsconfig.json`
+  keeps `strict` on yet sets `noImplicitAny: false`, because the app mostly
+  orchestrates the already-strictly-typed core (`scripts/`), and annotating every
+  internal SQLite-handle helper would be high-cost, low-value churn. Types are
+  added where they matter: the core-consumption seam (`BuildIndexOptions`/
+  `BuildIndexResult`, `FileInfo`), the service/worker factories, and the IPC
+  bridge. Module-to-module specifiers use the real `.ts` extension (mirroring
+  `scripts/`, since Node's type-stripping does not rewrite `.js`→`.ts`), which
+  needs `allowImportingTsExtensions` (safe under the project's `noEmit`); the
+  worker's *runtime* path stays `indexer-worker.js` because that is the built
+  output. `@types/better-sqlite3` is a devDependency for the injected binding.
+
+**Two-tier typechecking.** `npm run typecheck` runs the root project (`scripts/` +
+`tests/`, fully strict including `noImplicitAny`) and then the app project. The
+root project **excludes the app-importing tests** (`tests/app-*.test.mjs`,
+`tests/recap-capture-query.test.mjs`): those tests import app source, which would
+otherwise drag the lenient app files into the strict root program and fail on
+implicit `any`. The app source is instead covered by `app/tsconfig.json`, so
+nothing loses type coverage — the strict core and the lenient app are checked by
+the project that owns each, and never mixed.
 
 **Consequences.** The app is restructured into `src/{main,preload,renderer}` with
-`electron.vite.config.ts`; each main module is a build input so CommonJS-style
-require resolution and the indexer worker (`{ type: 'module' }`) resolve at
-runtime. `npm run dev` is `electron-vite dev`. Tests that loaded app modules moved
+`electron.vite.config.ts`; each main module is a build input so relative imports
+between them and the indexer worker (`{ type: 'module' }`) resolve at runtime.
+`npm run dev` is `electron-vite dev`. Tests that loaded app modules moved
 to ESM imports, and `app-main-settings` was rewritten from CJS `Module._load`
 mocking to `node:test` `mock.module` (needs `--experimental-test-module-mocks`).
 A future contributor may be tempted to make the preload ESM or disable the
diff --git a/package.json b/package.json
index 21af195..0285b46 100644
--- a/package.json
+++ b/package.json
@@ -7,7 +7,7 @@
   "license": "AGPL-3.0",
   "scripts": {
     "test": "node --experimental-test-module-mocks --test tests/*.test.mjs",
-    "typecheck": "tsc --noEmit",
+    "typecheck": "tsc --noEmit && tsc --noEmit -p app/tsconfig.json",
     "lint": "eslint .",
     "build:core": "rm -rf dist && tsc -p tsconfig.build.json"
   },
diff --git a/tests/app-indexer-service.test.mjs b/tests/app-indexer-service.test.mjs
index 7e23903..52b92ac 100644
--- a/tests/app-indexer-service.test.mjs
+++ b/tests/app-indexer-service.test.mjs
@@ -6,7 +6,7 @@ import { tmpdir } from 'node:os';
 import { join } from 'node:path';
 
 const require = createRequire(import.meta.url);
-import { createIndexerService } from '../app/src/main/indexer-service.js';
+import { createIndexerService } from '../app/src/main/indexer-service.ts';
 
 function manualTimers() {
   const timers = new Set();
diff --git a/tests/app-indexer-worker-client.test.mjs b/tests/app-indexer-worker-client.test.mjs
index 83233e1..2d074be 100644
--- a/tests/app-indexer-worker-client.test.mjs
+++ b/tests/app-indexer-worker-client.test.mjs
@@ -3,7 +3,7 @@ import assert from 'node:assert/strict';
 import { createRequire } from 'node:module';
 
 const require = createRequire(import.meta.url);
-import { createWorkerBuildIndex } from '../app/src/main/indexer-worker-client.js';
+import { createWorkerBuildIndex } from '../app/src/main/indexer-worker-client.ts';
 
 test('worker build client resolves build results from a worker thread', async () => {
   const instances = [];
diff --git a/tests/app-indexer.test.mjs b/tests/app-indexer.test.mjs
index 1095c85..9599986 100644
--- a/tests/app-indexer.test.mjs
+++ b/tests/app-indexer.test.mjs
@@ -6,7 +6,7 @@ import { tmpdir } from 'node:os';
 import { join } from 'node:path';
 
 const require = createRequire(import.meta.url);
-import { buildIndex } from '../app/src/main/indexer.js';
+import { buildIndex } from '../app/src/main/indexer.ts';
 const { DatabaseSync } = require('node:sqlite');
 
 class TestDatabase {
diff --git a/tests/app-main-settings.test.mjs b/tests/app-main-settings.test.mjs
index fb99aa0..2010e2e 100644
--- a/tests/app-main-settings.test.mjs
+++ b/tests/app-main-settings.test.mjs
@@ -22,7 +22,7 @@ const require = createRequire(import.meta.url);
 // resolve each bare specifier exactly as the main module sees it (ESM resolution
 // relative to the main module's directory) and mock that URL. Relative deps are
 // resolved against the main module URL directly.
-const mainUrl = new URL('../app/src/main/index.js', import.meta.url);
+const mainUrl = new URL('../app/src/main/index.ts', import.meta.url);
 const mainPath = fileURLToPath(mainUrl);
 const mainDir = fileURLToPath(new URL('.', mainUrl));
 
@@ -37,9 +37,9 @@ function esmResolve(specifier) {
 const ELECTRON_URL = esmResolve('electron');
 const DATABASE_URL = esmResolve('better-sqlite3');
 const CHOKIDAR_URL = esmResolve('chokidar');
-const INDEXER_URL = new URL('./indexer.js', mainUrl).href;
-const INDEXER_SERVICE_URL = new URL('./indexer-service.js', mainUrl).href;
-const INDEXER_WORKER_URL = new URL('./indexer-worker-client.js', mainUrl).href;
+const INDEXER_URL = new URL('./indexer.ts', mainUrl).href;
+const INDEXER_SERVICE_URL = new URL('./indexer-service.ts', mainUrl).href;
+const INDEXER_WORKER_URL = new URL('./indexer-worker-client.ts', mainUrl).href;
 
 let importCounter = 0;
 
diff --git a/tests/recap-capture-query.test.mjs b/tests/recap-capture-query.test.mjs
index 1d7d4dd..0186f7b 100644
--- a/tests/recap-capture-query.test.mjs
+++ b/tests/recap-capture-query.test.mjs
@@ -3,7 +3,7 @@ import assert from 'node:assert/strict';
 import { createRequire } from 'node:module';
 
 const require = createRequire(import.meta.url);
-import { buildRecapExportQuery, cleanRecapFilename } from '../app/src/main/recap-capture-query.js';
+import { buildRecapExportQuery, cleanRecapFilename } from '../app/src/main/recap-capture-query.ts';
 
 test('recap export query includes the selected recap filename', () => {
   const query = buildRecapExportQuery({
diff --git a/tsconfig.json b/tsconfig.json
index e28485c..95cd83d 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -16,5 +16,12 @@
     "forceConsistentCasingInFileNames": true
   },
   "include": ["scripts/**/*", "tests/**/*"],
-  "exclude": ["node_modules", "app", "dist", "release"]
+  "exclude": [
+    "node_modules",
+    "app",
+    "dist",
+    "release",
+    "tests/app-*.test.mjs",
+    "tests/recap-capture-query.test.mjs"
+  ]
 }