How do you troubleshoot a Micronaut bean that fails to inject due to ambiguous qualifiers?

An ambiguous injection error, where Micronaut reports multiple candidate beans for a single injection point, happens when more than one bean implements the same injected type and none is marked as the one to prefer.

public interface NotificationSender {}

@Singleton
public class EmailSender implements NotificationSender {}

@Singleton
public class SmsSender implements NotificationSender {}

Injecting NotificationSender directly at this point fails to resolve. The fix is to disambiguate explicitly, using one of a few approaches:

1. Named qualifiers: annotate each implementation with @Named("email") and @Named("sms"), then inject with a matching @Named qualifier at the call site.
2. Custom qualifier annotations for stronger typing than string-based @Named.
3. @Primary on one implementation, marking it the default when no explicit qualifier is given.
4. Injecting a collection such as List<NotificationSender> instead of a single instance, when you actually want all implementations.

Reading the actual error message matters here; Micronaut's compile-time and startup validation typically names the exact injection point and the competing bean classes, which is usually enough to identify which of these four fixes applies without guesswork.