stack/docs/architecture/lease-broker-security.md

WI-1 lease broker security notes

• Trusted identity comes only from Linux SO_PEERCRED plus /proc starttime, never request identity fields.
• Descendant authorization is anchored to (pid,starttime) and uses a complete second starttime pass to fail closed on disappearance or PID-reuse races.
• Runtime generations are monotonic per anchor; a bump revokes prior-incarnation tokens before persistence commits.
• Session IDs and cycle tokens use the OS cryptographic RNG. Math.random and model output are not token sources.
• Framing and persistence failures fail closed. Sensitive tokens are not logged.
• Built-in 0700/0600 filesystem modes provide same-principal hardening only, not socket authenticity against the same UID. WI-1 provides no distinct-principal isolation. That stronger deployment requires an external protected proxy, ACL, or service boundary, and the boundary must preserve authenticated client identity for the broker's SO_PEERCRED and ancestry authorization rather than substituting a shared proxy identity.
• WI-2+ security surfaces—receipts, promotion transactions, mutator gates, hooks, payload construction, and recovery—are explicitly out of scope.

Coordinator security review must rerun the real socket/peercred acceptance suite on an unrestricted Linux runner and obtain the mandated independent Opus-SECREV review before integration.