Position in workflow: Terminal activity of Define Architecture (DTA) — order 20 of 20. Run only after all prior DTA domain activities are complete (DTA-02 through DTA-17, and when applicable Activity 200 Define AI Agent Architecture and Activity 201 Define MCP Architecture).

Write SAO.md (System Architecture Overview)

Objective

Compile all architectural decisions from DTA-02 through DTA-17 (and optionally Activities 200 and 201, if applicable) into a single, authoritative document: docs/architecture/SAO.md.

Since Activity 42 now dispatches the domain decision workers in parallel (see that activity's Step 6), this activity is the first point at which all 16-18 domain decisions are seen together. Serial execution used to give an agent incidental cross-domain awareness just by having read every earlier decision in order before reaching this activity; parallel dispatch does not provide that awareness, so Step 0 below makes the check explicit instead of assuming it happened.

Process

0. Cross-Domain Consistency Check (run before compiling)

Before writing anything into SAO.md, check each collected domain decision against the others for contradictions. At minimum, check these known collision points:

For each pair above (and any other conflict a reviewer notices while compiling): if the two decisions are compatible, note nothing extra. If they conflict, do not silently pick one — surface it to the user as a named contradiction between the two domains and get an explicit resolution before writing either section into SAO.md.

Record the outcome of this check (clean, or list of resolved contradictions) as a short note at the top of SAO.md's changelog/history, so a future reader can see the check happened.

1. Gather All Decisions

Collect recorded decisions from each domain activity:
- DTA-02: Application Blocks
- DTA-03: Integration & API Design
- DTA-04: Code Organization
- DTA-05: Data Architecture
- DTA-06: Test Strategy
- DTA-07: Performance & Scalability
- DTA-08: Error Handling & Resilience
- DTA-09: Infrastructure
- DTA-10: CI/CD Pipeline
- DTA-11: Release & Rollback
- DTA-12: Observability
- DTA-13: Config & Secrets
- DTA-14: Security
- DTA-15: Backup & Recovery
- DTA-16: Developer Experience
- DTA-17: Documentation Strategy
- Activity 200: AI Agent Architecture (if applicable)
- Activity 201: MCP Architecture (if applicable)

2. Write SAO.md

Structure — add sections 17 and 18 after section 16:

## 16. Documentation Strategy
[Decision from DTA-17]

## 17. AI Agent Architecture
[Decision from Activity 200 — skip section if no in-app agent]

## 18. MCP Architecture
[Decision from Activity 201 — skip section if no MCP interface]

3. Skill Gap Analysis

Compile coverage reports from all domain activities into a single matrix:

Domain                   | Covered Skills     | Gaps
Application Blocks       | [list]             | [list]
...
AI Agent Architecture    | [list]             | [list]
MCP Architecture         | [list]             | [list]

4. Review with User

Present SAO.md for review, including the Step 0 consistency-check outcome. Get explicit approval before proceeding to Bootstrap Project.

5. Post-Implementation Updates

The SAO is a living document. During and after implementation, update it with critical discoveries, retrospective corrections, and recurring patterns. Each update should reference the original DTA decision.

Deliverables

• Cross-domain consistency check performed and recorded (Step 0), any contradictions resolved with the user before compilation
• SAO.md written at docs/architecture/SAO.md
• All domain decisions (16 core + up to 2 optional: AI Agent, MCP) compiled
• Skill coverage report included
• Key decisions summary with rationale
• User approval obtained
• Ready to proceed to Define Software Process (DSP). DSP requires SAO.md to generate the AI IDE configuration — run DSP before BSP.

When ESM, DTA, DSP, and BSP are all complete, proceed to BSP-08 for the Construction Handoff and mode selection.