## Why

SentryAgent.ai is growing and hiring engineers with BSc Computer Science and one year of industrial experience. There are currently no internal engineering documents that explain how the system works from the top down — new engineers have no structured path from product vision to running code, and no reference for how to contribute correctly. This gap slows onboarding, increases mistakes, and risks divergence from our architecture and standards.

## What Changes

- New `docs/engineering/` directory added to the repository as the canonical engineering knowledge base
- Top-down documentation suite covering all layers of the system: company vision → architecture → codebase → services → workflows → operations
- Annotated code walkthroughs for the three most critical system flows (token issuance, agent registration, credential rotation)
- Development environment setup guide targeting < 30 minutes from clone to running local stack
- Engineering workflow guide covering the full OpenSpec → Architect → Developer → QA → merge cycle
- Service deep-dive documents for all 8 core services/components
- SDK integration guide covering all four language SDKs
- Testing strategy and quality gate reference
- Deployment and operations reference covering Docker, Terraform, and monitoring

## Capabilities

### New Capabilities

- `engineering-overview`: Company mission, product vision, system purpose, and how the engineering team operates — the entry point for all new hires
- `architecture-guide`: System architecture including component diagram, data flow diagrams, deployment topology, and technology stack rationale (ADRs)
- `codebase-structure`: Annotated directory map explaining every top-level directory and key file, what lives where and why
- `service-deep-dives`: Per-service documentation for AgentService, OAuth2Service, CredentialService, AuditService, VaultClient, OPA policy engine, Web Dashboard, and Prometheus/Grafana monitoring
- `code-walkthroughs`: Step-by-step annotated traces of the three critical flows: token issuance end-to-end, agent registration end-to-end, credential rotation end-to-end
- `dev-environment-setup`: Local development environment setup — prerequisites, clone, configure, Docker Compose up, smoke test — targeting < 30 minutes
- `engineering-workflow`: How to contribute — OpenSpec spec-first workflow, branching strategy, PR standards, quality gates, and the role of each virtual engineering team member
- `testing-strategy`: Test framework, test types (unit vs integration), coverage gates, how to run tests, and how to write new tests following project conventions
- `deployment-operations`: Docker build and run, Terraform multi-region deployment, environment configuration, Prometheus/Grafana monitoring, and operational runbooks
- `sdk-guide`: Integration guide for Node.js, Python, Go, and Java SDKs — installation, authentication, all major operations, error handling

### Modified Capabilities

_(none — this change adds documentation only; no existing spec-level behavior changes)_

## Impact

- **Repository**: New `docs/engineering/` directory (~15 documents, ~10,000 lines of markdown)
- **No code changes**: Documentation only — zero impact on `src/`, `tests/`, `sdk/`, or infrastructure
- **Dependencies**: None — no new packages required
- **APIs**: No API changes
- **Existing docs**: `docs/developers/` (bedroom developer guide) and `docs/devops/` (operations) remain unchanged; this is an additive engineering-internal knowledge base
