# Aggregation-Only Contract (AOC) Guardrails

The Aggregation-Only Contract keeps ingestion services deterministic and policy-neutral. Use these checkpoints whenever you add or modify backlog items:

1. **Ingestion writes raw facts only.** Concelier and Excititor append immutable observations/linksets. No precedence, severity, suppression, or "safe fix" hints may be computed at ingest time.
2. **Derived semantics live elsewhere.** Policy Engine overlays, Vuln Explorer composition, and downstream reporting layers attach severity, precedence, policy verdicts, and UI hints.
3. **Provenance is mandatory.** Every ingestion write must include original source metadata, digests, and signing/provenance evidence when available. Reject writes lacking provenance.
4. **Deterministic outputs.** Given the same inputs, ingestion must produce identical documents, hashes, and event payloads across reruns.
5. **Guardrails everywhere.** Roslyn analyzers, schema validators, and CI smoke tests should fail builds that attempt forbidden writes.

For detailed roles and ownership boundaries, see `AGENTS.md` at the repo root and the module-specific `ARCHITECTURE_*.md` dossiers.

Need the full contract? Read the [Aggregation-Only Contract reference](../ingestion/aggregation-only-contract.md) for schemas, error codes, and migration guidance.