PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/main/contributing-docs/commit-message-guidelines.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.dev application / infrastructure changes
• Other... Please describe:

What is the current behavior?

Issue Number: #4059

Motivation

Angular currently allows an ambiguous case for event binding on a component host: if an event name matches an @Output, but the same DOM event also bubbles from inside the component template, the parent handler may be attached as a fallback DOM listener even when the expected behavior is to subscribe only to the component output.

This makes the behavior non-obvious and harder to debug.

<custom-change (change)="onChange()"></custom-change>

@Component({
  selector: 'custom-change',
  template: '<input>', // bubbling native `change`
})
export class CustomChange {}

In this case, (change) on the component host may work through the fallback DOM mechanism because the native change event bubbles, even though the component does not declare an explicit change output.

The behavior feels "magical" and does not clearly signal an API issue in the component.

What is the new behavior?

<custom-change (change)="onChange()"></custom-change>

@Component({
  selector: 'custom-change',
  template: '<input (change.prevent)="...">'
})
export class CustomChange {}

Does this PR introduce a breaking change?

• Yes
• No