Which @angular/* package(s) are relevant/related to the feature request?

No response

Description

With @defer (prefetch on viewport(header)), the prefetch setting usually has no effect. It is overridden by the default setting from the actual defer, which is idle.

Users might be confused because they expect a different behaviour.

There are similar settings where the prefetch would start after the defer.

Proposed solution

Those types of configuration settings could be auto-detected by Angular and communicated via an error message or warning.

Alternatives considered

@yjaaidi suggested that a defer setting could be mandatory once a prefetch has been set.