# Knowledge cache tiers

- **L0 — immutable session prefix:** trust boundaries, security policy, and stable protocol framing. Changes require explicit versioning and complete parity checks.
- **L1 — stable workflow contract:** agent definitions, query profiles, and output contracts. Changes invalidate the affected workflow cache.
- **L2 — reviewed reference knowledge:** design guidance and component specifications. Entries may evolve independently through catalog hashes.
- **L3 — volatile project evidence:** project context and connector evidence. It is scoped, short-lived, and never shares a cache key across projects.

Moving material into a more stable tier requires evidence that its authority, audience, and update cadence match that tier. Cache stability never overrides project isolation or freshness checks.