docs: add SCOPE.md for rapid orientation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SCOPE.md

@@ -0,0 +1,101 @@
+# SCOPE
+
+> This file helps you quickly understand what this repository is about,
+> when it is relevant, and when it is not.
+> It is intentionally lightweight and may be incomplete.
+
+---
+
+## One-liner
+
+S1 Infrastructure Substrate of the Railiance OAS Stack — Git-driven OS provisioning, security hardening, and server baseline using Terraform, cloud-init, and Ansible.
+
+---
+
+## Core Idea
+
+Railiance is structured as five independent repos per OAS Stack layer. This repo is S1 — the foundation. It provisions bare-metal/cloud servers (Hetzner, HostEurope), hardens the OS, manages secrets (SOPS/age), and validates the resulting baseline with Goss tests. S1 must be converged and verified before any higher layer (Kubernetes, platform, etc.) can run.
+
+---
+
+## In Scope
+
+- OS provisioning via Terraform (Hetzner, HostEurope providers)
+- First-boot configuration via cloud-init
+- OS convergence via Ansible (base, security, sops_agent roles)
+- Security hardening and firewall rules
+- Secret management: SOPS/age encryption at rest in Git
+- Goss specification and test suite for OS baseline validation
+- Server inventory management (`inventory/servers.yaml` — source of truth)
+- SSH access management
+
+---
+
+## Out of Scope (per ADR-003)
+
+- Kubernetes runtime → railiance-cluster (S2)
+- Platform services → railiance-platform (S3)
+- Developer tooling → railiance-enablement (S4)
+- Application deployments → railiance-apps (S5)
+- No cross-layer re-configuration from higher layers
+
+---
+
+## Relevant When
+
+- Provisioning new servers for the Railiance stack
+- OS hardening, Ansible convergence, or Goss verification
+- Managing server inventory or SSH access
+- Rotating SOPS/age keys or updating secrets
+
+---
+
+## Not Relevant When
+
+- Kubernetes, platform services, or application work (wrong layer)
+- Server is already provisioned and converged (use cluster/platform repos)
+
+---
+
+## Current State
+
+- Status: active / productive
+- Implementation: single-server HostEurope baseline complete (RAIL-HO-WP-0001); server spec + test suite active (WP-0002); 5-repo stack restructure active (WP-0003)
+- Stability: high for single-server bootstrap; proven in production (92.205.62.239)
+- Usage: foundation for all Railiance deployments; used daily for convergence and verification
+
+---
+
+## How It Fits
+
+- Upstream dependencies: Terraform, Ansible, SOPS/age (external tools); cloud provider APIs
+- Downstream consumers: railiance-cluster (S2) depends on a converged, verified OS from this layer; all higher layers transitively depend on S1
+- Often used with: railiance-cluster (next layer), ops-bridge (SSH tunnel for remote State Hub access)
+
+---
+
+## Terminology
+
+- Preferred terms: OAS Stack Level S1, convergence, verification, SOPS/age, Goss specification, boundary rule
+- Potentially confusing terms: "convergence" = applying Ansible to reach desired state; "verification" = running Goss tests to validate it
+
+---
+
+## Related / Overlapping Repositories
+
+- `railiance-cluster` (S2) — consumes the OS baseline provided by S1
+- `ops-bridge` — used to reach local State Hub from remote HostEurope server
+
+---
+
+## Getting Oriented
+
+- Start with: `CLAUDE.md` (session protocol, remote execution), `README.md` (provisioning workflow)
+- Key files / directories: `inventory/servers.yaml` (authoritative server list), `ansible/` (playbooks/roles), `terraform/` (provider configs), `goss/` (spec + tests), `docs/adr/ADR-003-railiance-5repo-stack-architecture.md`
+- Entry points: `make tf-plan`, `make tf-apply`, `make converge`, `make verify`
+
+---
+
+## Notes
+
+Designed for remote execution from HostEurope (92.205.130.254). SSH reverse tunnel required for State Hub access: `ssh -R 8000:127.0.0.1:8000 tegwick@92.205.130.254`.