❌ Incorrect (did-update):

// app/components/user-greeting.gjs
import Component from '@glimmer/component';
import { tracked } from '@glimmer/tracking';
import { action } from '@ember/object';

class UserGreeting extends Component {
  @tracked displayName = '';

  @action
  updateDisplayName() {
    // Runs on every render - inefficient and error-prone
    this.displayName = `${this.args.user.firstName} ${this.args.user.lastName}`;
  }

  <template>
    <div {{did-update this.updateDisplayName @user}}>
      Hello,
      {{this.displayName}}
    </div>
  </template>
}