Cross-domain infrastructure packages reused across services and domains (SubmitQueue, Stovepipe, and other repo-local services). These are foundational building blocks — not domain entities, not pluggable extensions — and they carry no domain dependencies.

For infrastructure shared only within a single domain (across that domain's own gateway and orchestrator), see the domain-scoped core/ package, e.g. submitqueue/core/ (which holds the queue consumer framework and the request lifecycle).

• errs/ — Error classification framework. Classifies errors by origin (user vs. infra) and retryability. Extensions return plain errors; service controllers classify them.
• httpclient/ — Shared HTTP transport helpers (timeouts, instrumentation) for extensions that talk to external services over HTTP.
• metrics/ — Metrics utility helpers for tally.Scope. Provides standardized counters, timers, and histograms with error-aware tagging via core/errs integration.