How to avoid singleton database when setting up better auth

import { betterAuth } from "better-auth";
import { drizzleAdapter } from "better-auth/adapters/drizzle";
import { db } from "@/db"; // your drizzle instance

export const auth = betterAuth({
    database: drizzleAdapter(db, {
        provider: "pg", // or "mysql", "sqlite"
    }),
});

// lib/auth.ts
export function initAuth(db: DB) {
  return betterAuth({
    database: drizzleAdapter(db, { provider: 'pg' })
  });
}

// index.ts
async function main() {
  ...

  const db = await openDB({ config: config.value });
  if (db.isErr()) {
    ...
  }

  const { runMigrations } = await getMigrations(initAuth(db.value) as BetterAuthOptions);
  await runMigrations();
  
  ...
}

await main();

2025-09-24T02:44:44.487Z WARN [Better Auth]: Could not determine database type, defaulting to sqlite. Please provide a type in the database options to avoid this.
2025-09-24T02:44:44.488Z ERROR [Better Auth]: Only kysely adapter is supported for migrations. You can use `generate` command to generate the schema, if you're using a different adapter.