export async function register() {
  console.log('[instrumentation] register() called, NEXT_RUNTIME =', process.env.NEXT_RUNTIME)
  if (process.env.NEXT_RUNTIME === 'nodejs') {
    const fs = await import('fs')
    const path = await import('path')
    const journal = path.join(process.cwd(), 'lib/db/migrations/meta/_journal.json')

    if (!fs.existsSync(journal)) {
      console.warn('[migrations] No journal found at', journal, '— skipping')
      return
    }

    console.log('[migrations] Applying migrations...')
    try {
      const postgres = (await import('postgres')).default
      const { drizzle } = await import('drizzle-orm/postgres-js')
      const { migrate } = await import('drizzle-orm/postgres-js/migrator')

      // Dedicated single connection for migrations — never share with the app pool
      const client = postgres(process.env.DATABASE_URL!, { max: 1, connect_timeout: 10 })
      const db = drizzle(client)
      await migrate(db, { migrationsFolder: './lib/db/migrations' })
      await client.end()
      console.log('[migrations] Done')
    } catch (err) {
      console.error('[migrations] Failed:', err)
    }
  }
}