EPIC: Authority and security

Programme: #1

Own the threat model, capability authorization, credential/data protection, process/egress confinement, privacy governance and incident response. Security rules are product semantics: model/provider output can propose work but cannot authorize itself.

## Child issues
- [ ] #6 SEC-01 — Threat model and conformance policy
- [ ] #7 SEC-02 — Capability broker and scoped grants
- [ ] #8 SEC-03 — Vault, encryption and information-flow controls
- [ ] #9 SEC-04 — Sandbox and egress broker
- [ ] #10 SEC-05 — Privacy governance and incident process

## Cross-cutting gates
No ambient authority, scoped credentials, trusted approval surfaces, hostile content never grants privilege, explicit egress, revocation, reconciliation and auditable decisions.

Start with child issues #6–#10 and review the cross-cutting gates in this epic. Map how each child addresses threat modeling, scoped authority, protection, confinement, privacy, or incident response; the epic is done when those child issues are resolved and the stated security gates are satisfied.

Written by the indexing model from the issue text.