fix: open sqlite lazily so parallel build workers stop locking the file

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/db.ts

@@ -5,9 +5,15 @@ import { randomUUID } from "node:crypto";
 const dir = process.env.DATA_DIR ?? "data";
 mkdirSync(dir, { recursive: true });
 
-const g = globalThis as { __qaiDb?: DatabaseSync };
-export const db = (g.__qaiDb ??= (() => {
+// Open on first query, not at import: `next build` imports every page through lib/auth -> lib/db in ~6 parallel
+// workers, and six processes running DDL against one file at once fails with "database is locked".
+let _db: DatabaseSync | null = null;
+function openDb(): DatabaseSync {
+  if (_db) return _db;
   const d = new DatabaseSync(`${dir}/qai.db`);
+  d.exec(`
+    PRAGMA journal_mode = WAL;
+    PRAGMA busy_timeout = 5000;`);
   d.exec(`
     PRAGMA journal_mode = WAL;
     CREATE TABLE IF NOT EXISTS users (
@@ -25,8 +31,17 @@ export const db = (g.__qaiDb ??= (() => {
       status TEXT NOT NULL DEFAULT 'running', error TEXT,
       created_at INTEGER NOT NULL, updated_at INTEGER NOT NULL);
     CREATE INDEX IF NOT EXISTS ix_analyses_user ON analyses(user_id, created_at DESC);`);
+  _db = d;
   return d;
-})());
+}
+// Proxy keeps the terse call sites (db.prepare) while deferring the open; methods must be bound to the real
+// instance or node:sqlite rejects the receiver ("Illegal invocation").
+export const db: DatabaseSync = new Proxy({} as DatabaseSync, {
+  get: (_t, k) => {
+    const v = (openDb() as any)[k];
+    return typeof v === "function" ? v.bind(openDb()) : v;
+  },
+});
 
 const now = () => Date.now();
 type Row = string | number | null;