Shared infrastructure packages reused across services. These are internal building blocks — not domain entities, not pluggable extensions, but foundational components that services depend on directly.

• consumer/ — Queue message consumption framework. Manages subscription lifecycle, message routing to controllers, automatic ack/nack, error classification (retryable vs. poison pill), and graceful shutdown. Services register Controller implementations and the consumer handles the rest.
• errs/ — Error classification framework. Classifies errors by origin (user vs. infra) and retryability. Extensions return plain errors; service controllers classify them.
• metrics/ — Metrics utility helpers for tally.Scope. Provides standardized counters, timers, and histograms with error-aware tagging via core/errs integration.