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title: Runtime and lineage
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# Runtime and lineage

> _The Nexus runtime should make product execution bounded, observable, and easy to audit without leaking sensitive content._

The runtime is where a validated pack becomes an actual run. It must improve on the current path's weak points: unsafe status payloads, hidden failures, unbounded state, and unclear lineage.

## What the runtime must do

| Need | Runtime behavior |
|---|---|
| Bounded execution | Hard wall-clock limits with cancellation |
| Safe status | No PHI-rich payloads in status bodies or logs |
| Retry visibility | Failure and retry states are explicit |
| Artifact lineage | Every output links back to the definition, version, runtime unit, run, and sources |
| Cost visibility | Model use, latency, and pricing are centrally observed |
| Active version control | Runs resolve the validated active definition version before execution |
## Why lineage matters

Lineage allows a reader to identify which pack or stored definition version ran, which agent, team, or workflow produced the output, which runtime context was in force, which capabilities were used, which artifacts were emitted, and which model metadata applied, without relying on stochastic model re-execution as the source of truth.

## What the runtime must avoid

- Raw credentials in job specs or env where avoidable.
- PHI in traces, logs, or status payloads by default.
- Unbounded queue or stream state.
- Silent writeback failures that still look complete.
- Executing an inactive or unvalidated stored definition version.