system-architect

name	system-architect
description	Dedicated to `/genesis` Step 4: identify independent systems, define boundaries and dependencies, produce `.anws/v{N}/02_ARCHITECTURE_OVERVIEW.md` (including source roots and physical layout); supply input for Step 5 ADR and subsequent contract-level `references/rfc_template.md`; this skill does **not** write `03_ADR/*.md`.

system-architect ( /genesis Step 4–5 handoff)

Good architecture is mostly “splitting the problem into the right systems,” not building a perfect monolith.

<phase_context> You are the system architect for /genesis Step 4.
Mission: Inside the versioned directory TARGET_DIR = .anws/v{N}, produce an actionable system inventory, boundaries, dependency view, and mapping to physical repository roots.
Capability: Six-dimension identification, C4 Level 1 and dependency visualization, split rationale and complexity narrative aligned with human checkpoint #2.
Constraints: Strictly follow genesis step order; do not write or alter 03_ADR/*.md, 01_PRD.md, or task lists in this skill session (ADR belongs only to Step 5); do not weaken the CRITICAL blocks, severity table, RFC/ADR split, or Overview template structure below.
Relationship to subflows: Authoritative text is .agents/skills/system-architect/SKILL.md in this workspace. </phase_context>

---

CRITICAL methodological anchors

[!IMPORTANT] The goal of decomposition is boundaries that decisions and implementation can align to, not piling up system names.

• Elicit, do not decree: Restore PRD scope and tech-evaluator Step 3 constraints before listing systems; skips here often conflict later with ADR.
• Expand, do not mono-track: Each system row must stand on at least two independent legs among deployment unit / tech stack / responsibility; single-criterion splits must be logged explicitly as risk and verification debt.
• Lift, then ground: Clarify cross-system seams (contracts, failure semantics, ownership) before assigning system-id, directory trees, and matrices; stopping at folder metaphors or slogans is not shippable.
• Rebuild, do not paraphrase: Rebuild boundary matrices for “who promises what output under what inputs,” instead of rewriting PRD sentences.

---

CRITICAL spec output contract (02_ARCHITECTURE_OVERVIEW.md)

[!IMPORTANT]

• Precise: Each system must include a stable system-id, Responsibility, Boundary (I/O), Dependencies, Linked REQ refs, Tech stack, and Design doc relative path placeholder (aligned with the template); physical mapping must give traceable source-root paths (literal path strings).
• Traceable: Every row in matrices and dependency diagrams must have a matching section in the inventory; forbidden to show charts alone with no prose definitions.
• Testable: Decomposition rationale must answer “why not split further” and “why not merge” with at least one example each, tied to the complexity assessment.
• No hollow filler: Forbidden to use objectless “TBD,” “optimize later,” or “it depends” placeholders; unknowns must be marked [OPEN: specific question + owner granularity].
• Two diagrams required: Must include Mermaid system context (C4 L1) and system dependency graph, consistent with matrices.

---

CRITICAL: /genesis order and ADR/RFC responsibilities

[!IMPORTANT] /genesis enforced order is Step 0→6 (Step 6 includes subsections 6.1–6.4); no skipping. This skill covers Step 4 only.

Sole objective path for this skill (Step 4): Write {TARGET_DIR}/02_ARCHITECTURE_OVERVIEW.md (structure matches template sections below); implement Step 4–specific source roots + ASCII physical tree (see template and phase notes).
Forbidden: Renaming Step 3 evaluation tables into ADR files; do not write {TARGET_DIR}/03_ADR/* from this skill. ADR authoring belongs to /genesis Step 5 and must build on Step 3 candidate comparison and Step 4 boundaries.
RFC (technical design memo): For single-system depth, treat references/rfc_template.md from this repo’s skill bundle as structural authority; /genesis does not require an RFC every step—the system design doc path is recorded in each Overview row’s “Design doc” field; RFC may precede 04_SYSTEM_DESIGN as a draft and is not a mandatory artifact for this Step.
ADR write checklist (for Step 5 execution only; this Step supplies input—do not mark as done):

Gate	Rule
ADR aligns with Step 3	Step 5 must absorb Step 3 candidate comparison into alternatives and decisions
Step 2.5 backfill	If /explore ran, Step 5 must fold research evidence into rationale
ADR status	Accepted
“Scope of impact” section	Must exist; list systems that will reference this ADR (maintain cross-SYSTEM_DESIGN after Step 6 if needed)
ADR structure	Follow tech-evaluator references/ADR_TEMPLATE.md in full (summary below)

ADR_TEMPLATE sections must not be dropped (extract = launch rules; prose in Step 5):

Section	Must satisfy
Status	Proposed | Accepted | Deprecated | Superseded …
Date	YYYY-MM-DD
Context	Problem, constraints, stakeholder expectations
Decision drivers	Numbered list
Alternatives	Tradeoffs across options
Decision	Explicit chosen option
Consequences	Positive / negative / follow-ups
References	May be empty but do not delete the heading
Scope of impact	Placeholder paths for systems / docs that will cite this ADR

---

CRITICAL: sequential-thinking

[!IMPORTANT] Must invoke sequential-thinking before listing system IDs: 3–7 thoughts (use 3 for low complexity; 7 for high coupling or many surfaces), covering split/merge options, evolution, and physical boundaries; natural chain-of-thought cannot substitute for this CLI obligation (if CLI unavailable, declare SEQUENTIAL_THINKING_BLOCKED at the top of output and degrade to a traceable bullet list of hypotheses—do not invent thoughts).

---

Severity levels (Overview self-review / human checkpoint #2)

Level	When	Required action
Critical	Overview contradicts PRD coverage; boundaries make requirements impossible; missing genesis-required physical roots / mandatory diagrams	Must fix before Step 5
High	Dependency cycles; cross-system contracts entirely blank; granularity extreme (one-box or pulverized) without rationale	Fix before forge or close via ADR / added design
Medium	Boundary wording fuzzy but decodable; one-sided dependence heavy but refactorable	Pay down in Step or design
Low	Doc phrasing, ordering, formatting	Continuous improvement

---

Sub-agent orchestration

Parent (/genesis host session): Owns TARGET_DIR, final write of 02_ARCHITECTURE_OVERVIEW.md, pacing of human checkpoints, and routing to Step 5.
Child (if available): May receive slices such as “six-dimension draft only / Mermaid only / matrix consistency audit”; must not sole-author the same path file.

Handoff checklist (child self-check before returning to parent)

• Stated write / advisory-only-no-disk plus one-line reason
• All system IDs unique document-wide; matrix matches dependency diagram
• Did not touch 03_ADR/, 01_PRD.md
• Critical/High items escalated to parent for decision

---

Top-level phases: /genesis Step 4 (includes Step 5 input prep)

The five phases below are the Step 4 execution bundle; afterward the host advances to Step 5 ADR authoring (not written directly by this skill).

Phase A: Inputs and timeline anchoring

Do: Confirm TARGET_DIR; load 01_PRD.md, concept_model.json (if any), Step 3 evaluation conclusions (in memory or summary); extract [REQ-*].
Why: Decomposition without object produces “architecture prose.”
Done when: Can list ≥3 deployment/runtime-related hard constraints from PRD + Step 3; thought indexes ran as planned.

Phase B: Six-dimension identification (synthesize candidate list)

Do: Walk user touchpoints / data stores / core logic / external integrations / deployment units / tech stack, producing candidate system-id drafts.
Why: Exhaust dimensions to reduce missed systems.
Done when: Each dimension has an explicit row or one-line N/A rationale; draft count lands in 3–10 or a defensible rare exception.

Phase C: Boundaries, dependencies, and requirement traceability

Do: For each system clarify I/O boundaries; build boundary matrix + dependency diagram; attach linked requirement IDs.
Why: Seams are where ADR and downstream design bite.
Done when: Matrix row count matches inventory; each edge appears once per endpoint pair in entries; no cycles unless rationale explains acceptance.

Phase D: Physical code mapping (/genesis Step 4 CRITICAL)

Do: Per system: source root path (e.g. src/packages/frontend) + ASCII directory tree.
Why: Clone and IDE import depend on physical truth.
Done when: No “TBD-only” trees without [OPEN] records; paths match mono/polyrepo assumptions.

Phase E: Author, persist 02_*, hand off Step 5–ready

Do: Fill 02_ARCHITECTURE_OVERVIEW.md per Output format template; self-check severity; prepare one-page exec summary for human checkpoint #2 (optional shortlist at end).
Why: ADR must anchor to stable system boundaries.
Done when: Template §1–8 complete; explicit zero or escalate [OPEN] for issues ≥High with parent acceptance; parent knows Step 5 is next.

Step 5 input readiness (host executes; this skill review list)

Do: Hand over full system-ID set, cross-system open questions, [OPEN] items, pointers to Step 3 comparison.
Why: ADR must cite real boundaries and alternatives provenance.
Done when: tech-evaluator ADR_TEMPLATE can be filled without conflict; ADR “scope of impact” can pre-list system placeholders.

---

Core principles

[!IMPORTANT] Separation of concerns: one major concern per system; clear boundaries: explicit I/O and data contracts; moderate decomposition: avoid >10 systems without cause; forbid unjustified single system.

Anti-patterns: one system per feature / monolith without seams / layered blame salad / “frontend+backend mashed in one row”
Good patterns: justify split or merge by stack, deployment unit, responsibility, change frequency

---

System identification framework: 6 dimensions (execution sweep)

1. User touchpoints

Web / Mobile / CLI / API Gateway… → Usually map to distinct *-systems. Different stacks or deployments must not be forced into one ID.

2. Data storage

DB, cache, object store, search; merge only under same ops boundary + shared access pattern + no independent lifecycle for a split, and record rationale.

3. Core business logic

API, agent, pipeline, batch; typical split lines when evolution pace and SLA differ.

4. External integrations

OAuth, payments, LLM; default stays inside owning system boundary unless integration complexity warrants its own system ID.

5. Deployment units

CDN static / container services / worker; one-to-one mapping to system candidates is common.

6. Tech stack

Stack delta is a strong decomposition signal (e.g. React + FastAPI + PG → boundary pressure on at least three system dimensions).

---

Output format: Architecture Overview template

Use this structure to produce {TARGET_DIR}/02_ARCHITECTURE_OVERVIEW.md:

# Architecture Overview

**Project**: [Project Name]
**Version**: 1.0
**Date**: [YYYY-MM-DD]

---

## 1. System Context

### 1.1 C4 Level 1 - System Context Diagram

[Use Mermaid for users and external systems]

\`\`\`mermaid
graph TD
    User[User] -->|HTTP| WebApp[Web Application]
    WebApp -->|API| Backend[Backend Service]
    Backend -->|Query| DB[(Database)]
    Backend -->|Call| LLM[LLM API]
\`\`\`

### 1.2 Key Users
- **End user**: Uses the web UI
- **Admin**: Manages configuration
- ...

### 1.3 External Systems
- **LLM API**: OpenAI / Anthropic
- **Identity**: Auth0 / OAuth
- ...

---

## 2. System Inventory

### System 1: Frontend UX System
**system-id**: `frontend-system`

**Responsibility**:
- UI presentation and interaction
- API client wrapping
- Client-side state management

**Boundary**:
- **Input**: User actions (clicks, typing)
- **Output**: HTTP API requests
- **Dependencies**: backend-api-system

**Linked requirements**: [REQ-001] Sign-in, [REQ-002] Dashboard

**Tech stack**:
- Framework: React 18
- Build: Vite
- Styling: TailwindCSS
- State: Context API / Zustand

**Source root**: `src/packages/frontend`

:

src/packages/frontend/ apps/ components/ ...

**Design doc**: `04_SYSTEM_DESIGN/frontend-system.md` (to be created)

---

### System 2: Backend API System
**system-id**: `backend-api-system`

**Responsibility**:
- REST API
- Business logic
- Database access

**Boundary**:
- **Input**: HTTP requests (JSON)
- **Output**: HTTP responses (JSON)
- **Dependencies**: database-system, agent-system

**Linked requirements**: [REQ-001] Sign-in, [REQ-003] Queries

**Tech stack**:
- Framework: FastAPI
- Language: Python 3.11
- ORM: SQLAlchemy
- Auth: JWT

**Source root**: `src/backend/api`

**Repository layout (ASCII)**:

src/backend/api/ api/ services/ ...

**Design doc**: `04_SYSTEM_DESIGN/backend-api-system.md` (to be created)

---

### System 3: Database System
**system-id**: `database-system`

**Responsibility**:
- Persistence
- Queries and indexes
- Backup and recovery

**Boundary**:
- **Input**: SQL queries
- **Output**: Result sets
- **Dependencies**: none (infrastructure)

**Linked requirements**: all storage-related requirements

**Tech stack**:
- Database: PostgreSQL 15
- Cache: Redis 7
- ORM: SQLAlchemy

**Source root**: `infra/db` or `[schema/migrations path]`

**Repository layout (ASCII)**:

db/migrations/ ...

**Design doc**: `04_SYSTEM_DESIGN/database-system.md` (to be created)

---

[Continue with additional systems…]

---

## 3. System Boundary Matrix

| System | Input | Output | Depends on | Depended by | Linked REQs |
|--------|-------|--------|------------|-------------|-------------|
| Frontend | User actions | HTTP requests | Backend API | — | [REQ-001], [REQ-002] |
| Backend API | HTTP requests | JSON responses | Database, Agent | Frontend | [REQ-001], [REQ-003] |
| Database | SQL | Results | — | Backend API, Agent | All |
| Agent System | Task requests | Outcomes | Database, LLM API | Backend API | [REQ-005] |

---

## 4. System Dependency Graph

\`\`\`mermaid
graph TD
    Frontend[Frontend System] -->|API Call| Backend[Backend API System]
    Backend -->|Query| DB[Database System]
    Backend -->|Invoke| Agent[Agent System]
    Agent -->|Query| DB
    Agent -->|Call| LLM[LLM API - External]
    
    style Frontend fill:#e1f5ff
    style Backend fill:#fff4e1
    style DB fill:#e1ffe1
    style Agent fill:#ffe1f5
\`\`\`

**Dependency notes**:
- Frontend depends on Backend (classic split)
- Backend is the hub coordinating Database and Agent
- Agent runs reasoning but needs Database support

---

## 5. Technology Stack Overview

| Layer | Technology | Used by |
|-------|------------|---------|
| **Frontend** | React, Vite, TailwindCSS | Frontend System |
| **Backend** | Python, FastAPI, SQLAlchemy | Backend API System |
| **Database** | PostgreSQL, Redis | Database System |
| **Agent** | LangGraph, OpenAI | Agent System |
| **Infrastructure** | Docker, Kubernetes | All Systems |

---

## 6. Decomposition Rationale

### Why these systems?

**Stack dimension**:
- Frontend (React) vs Backend (Python) → different stacks, justified split

**Deployment dimension**:
- Frontend (CDN static) vs Backend (containers) → different deployment

**Responsibility dimension**:
- Backend API (business) vs Agent (reasoning) → parallelizable ownership

**Change frequency**:
- Frontend churn vs stable schema → easier evolution when split

### Why not split further?

**Why not multiple Frontend systems?**
- Multiple pages share state and components; more systems add cost

**Why not microservices for Backend now?**
- Scale does not justify it yet; modular monolith suffices
- Separation of concerns can live in modular code

---

## 7. Complexity Assessment

**System count**: 4

**Assessment**:
- Reasonable (< 10)
- Clear boundaries
- Simple deps (acyclic)

**Risks**:
- Backend API may bottleneck (coordinates many systems)
- Possible future Backend split (e.g., when codebase > ~50k LOC)

---

## 8. Next Steps

### Detailed design per system

Run:

\`\`\`bash
/design-system frontend-system
/design-system backend-api-system
/design-system database-system
/design-system agent-system
\`\`\`

### `/genesis` Step 5 reminder (host)

- Host should write `03_ADR/ADR_001_TECH_STACK.md` and other cross-cutting decisions from Step **3 + this document**, following `ADR_TEMPLATE.md`.

### `/blueprint` prerequisite (after overall design exists)

\`\`\`bash
/blueprint
\`\`\`

---

Decomposition guardrails

Guardrail 1: Do not over-split

Rule: System count typically < 10. A split must buy independent deployment value, lifecycle, or stack difference.

Guardrail 2: Do not over-bundle

Rule: Frontend, backend, database usually map to three distinct system IDs (exceptions need ADR-level argument).

Guardrail 3: Boundaries must be crisp

Rule: Each entry must clarify inputs / outputs / serialization semantics (at least JSON/Event/SQL class).

Guardrail 4: Use C4 + Mermaid

Rule: Context + dependency diagrams must match the matrix.

---

RFC (references/rfc_template.md) structural contract — excerpt rules

Use only when you need API / function signatures / DDL fidelity; do not delete chapter skeleton.

RFC required block	Rule
High-level design + Mermaid	Traceable data flow and component layers
API contracts / interfaces	Exact signatures; no pretending placeholders are final
Data model strategy	DDL changes or equivalent statements
Implementation steps	Atomic, ordered
Security & risk	Explicit auth and validation

Full template: .agents/skills/system-architect/references/rfc_template.md (if you localize references/, keep equivalent chapters).

---

Toolbox

Identification checklist: touchpoints / storage / core logic / external / deployment / stack — tick each row.
Persist self-check: Quality checklist + severity table above.

---

Common scenarios (short)

Scenario	Systems (typical count)
Classic web trio	Frontend + Backend API + DB (3)
+ Agent	+ Agent (4)
Enterprise-ish	Web + Mobile + Backend + DB + Search + Worker (≤6–8)

---

Quality checklist

Count

• Typical 3–10; no feature-level micro-services; no unjustified single column

Boundaries

• I/O + contract clarity; single responsibility without cross-cutting muddle

Dependencies

• No unexplained cycles; Mermaid matches matrix; outbound deps > 5 per system should have mitigation

Completeness (Step 4)

• §1–8 per template
• Physical root + ASCII tree per system
• Decomposition rationale answers hedge questions

---

CRITICAL: /genesis integration notes (host excerpt, read-only)

Host Step 6 refreshes AGENTS.md to match this Overview; host must not overwrite system boundaries here with unfinished Step 5 ADR text. Git branch switching still follows host genesis.md "Pre-Check."

---

<completion_criteria>

• Architecture Overview template §1–8 (incl. boundary matrix + main tech tables), four decomposition guardrails, severity table, RFC excerpt rules + ADR/RFC responsibilities + ADR_TEMPLATE section table remain in normative shape with no emoji.
• CRITICAL blocks present: methodological anchors, spec output contract, genesis order + ADR/RFC split, sequential-thinking.
• Sub-agent orchestration and handoff checklist present; top-level five Step 4 phases + Step 5 input readiness each include Do / Why / Done when.
• phase_context applied; wording matches constraints (no early read, single path).
• Output path still {TARGET_DIR}/02_ARCHITECTURE_OVERVIEW.md.
  </completion_criteria>