# Architecture

> **Status:** Partially migrated. The lease-broker security-contract pages below are current references; the remaining architecture pages are still being classified.

This chapter is the canonical home for Mosaic Stack's system model, component boundaries, data and control flow, security model, architecture decisions, and RFCs. It explains why the system has its shape; it does not replace [`PRD.md`](../../PRD.md), [`TASKS.md`](../../TASKS.md), or the API contract.

## Promoted pages

- [`lease-broker-protocol.md`](lease-broker-protocol.md) — authenticated Unix-socket protocol, identity binding, framing, persistence, and lease transitions.
- [`lease-broker-security.md`](lease-broker-security.md) — identity, ancestry, filesystem, whole-class, observer, and named residual security boundaries.
- [`mutator-class-gate.md`](mutator-class-gate.md) — default-deny tool authorization, runtime adapters, launch choke point, and parser assurance boundary.
- [`compaction-revocation.md`](compaction-revocation.md) — Claude/Pi observer lifecycle, runtime generations, revocation, and the bounded residual stale window.

These pages are current security-contract references and are consumed by the lease-broker acceptance suites. Their live deployment gaps remain explicitly labeled in the pages; this migration does not change runtime behavior.

## Planned pages

| Path                 | Purpose                                                               | Status         |
| -------------------- | --------------------------------------------------------------------- | -------------- |
| `system-overview.md` | Platform boundary and major request, event, and agent-runtime flows.  | Planned.       |
| `component-map.md`   | Apps, packages, plugins, and dependency ownership.                    | Planned.       |
| `data-flow.md`       | Data, event, and control-plane movement.                              | Planned.       |
| `security-model.md`  | Trust boundaries, authority, authentication, and authorization model. | Planned.       |
| `decisions/`         | Approved architecture decision records.                               | Scaffold only. |
| `rfcs/`              | Proposals and protocol RFCs.                                          | Scaffold only. |

Promoted pages must be linked here, from [`DEVELOPER-GUIDE/README.md`](../README.md), and from [`SITEMAP.md`](../../SITEMAP.md). Do not create duplicate architecture pages in `docs/mosaic-stack/` or the docs root.

## Migration backlog — not current architecture

- [`docs/README.md`](../../README.md) — current documentation contract and placement rules.
- [`Documentation information architecture design`](../../plans/2026-08-10-docs-information-architecture-design.md) — approved documentation structure decision, not product architecture.
- [`Documentation catalog audit`](../../reports/documentation/2026-08-10-docs-catalog-audit.md) — evidence and migration recommendations, not normative architecture.
- [`_old_structure/architecture/`](../../_old_structure/architecture/) — remaining historical sources; each page requires classification and claim verification before promotion.

## Source-of-truth boundary

Architecture pages explain approved design and current system boundaries. Requirements remain in [`PRD.md`](../../PRD.md); active work remains in [`TASKS.md`](../../TASKS.md); executable behavior remains authoritative in source and tests. Draft proposals belong in `rfcs/` or [`docs/plans/`](../../plans/), with status clearly labeled.

## Related

- [[README|Documentation contract]]
- [[DEVELOPER-GUIDE/README|Developer guide]]
- [[PRD|Product requirements]]
- [[API/README|API index]]
