Packer PACKER_LOG alert threshold without losing step completion signals

Goal is to surface only actionable build problems to notification channels while keeping normal build progress in logs. Packer controls verbosity via PACKER_LOG with levels debug, info, warn, error, and the -debug flag forces full trace output regardless of the environment variable.

With PACKER_LOG at warn or error, informational step messages are suppressed, which reduces noise but also removes step-completion signals some CI systems use for alerting and progress tracking. The -debug flag overrides PACKER_LOG and can flood downstream notifications if not filtered.

Packer does not document a dedicated alert-only mode that emits warnings and errors on a separate stream from the main build log. This leaves an unresolved decision about how to keep useful alerts without losing progress context.

Does Packer provide a documented way to emit warnings and errors independently of the main log verbosity? How does the interaction between PACKER_LOG and -debug affect external alert thresholds? Is there a supported pattern for alert-only output without suppressing step completion information?