nw-design

name	nw-design
description	Designs system architecture with C4 diagrams and technology selection. Routes to the right architect based on design scope (system, domain, application, or full stack). Two interaction modes: guide (collaborative Q&A) or propose (architect presents options with trade-offs).
user-invocable	true
argument-hint	[component-name] - Optional: --residuality --paradigm=[auto|oop|fp]

NW-DESIGN: Architecture Design

Wave: DESIGN (wave 3 of 6) | Agents: Morgan (nw-solution-architect), nw-system-designer, nw-ddd-architect | Command: *design-architecture

Overview

Execute DESIGN wave through discovery-driven architecture design. The command starts with two interactive decisions:

1. Design Scope — routes to the right architect: system-level (@nw-system-designer), domain-level (@nw-ddd-architect), application-level (@nw-solution-architect), or full stack (all three in sequence).
2. Interaction Mode — guide (architect asks questions, you decide together) or propose (architect reads requirements, presents 2-3 options with trade-offs).

All architects write to docs/product/architecture/brief.md (SSOT), each in its own section. Analyzes existing codebase, evaluates open-source alternatives, produces C4 diagrams (Mermaid) as mandatory output.

Output Tiers (per D2)

Provenance: feature lean-wave-documentation — D2 (schema-typed sections), D10 (one-line expansion descriptions). Tier-1 [REF] sections (always emitted) + Tier-2 EXPANSION CATALOG items (lazy, on-demand) are the two output bands. Full contract: nWave/skills/nw-density-resolution-contract/SKILL.md.

Tier-1 [REF] — always emitted

Under ## Wave: DESIGN / [REF] <Section> headings:

• DDD list — D-numbered design decisions with verdicts and one-line rationale
• Component decomposition — table of components with paths and change types
• Driving ports — inbound surfaces (CLI, skill, HTTP) named per the C4 contract
• Driven ports + adapters — outbound side-effects with adapter mapping
• Technology choices — pinned languages/frameworks/runtime versions
• Decisions table — DDD-N row per locked decision (no rationale prose)
• Reuse Analysis table — every overlapping component classified EXTEND or CREATE NEW
• Open questions — items deliberately deferred to DISTILL/DELIVER

Tier-2 EXPANSION CATALOG — lazy, on-demand (per D10)

Rendered under ## Wave: DESIGN / [WHY|HOW] <Section> only when requested via --expand <id> (DDD-2), the wave-end menu (expansion_prompt = "ask"), mode = "full" auto-expansion, or an ad-hoc user request mid-session.

Expansion ID	Tier label	One-line description
trade-off-analysis	[WHY]	Quality-attribute trade-off matrix with prioritization rationale
rejected-alternatives	[WHY]	Architectures weighed and rejected with one-paragraph reason per option
c4-narrative	[HOW]	Long-form C4 walkthrough: System Context → Container → Component prose
evolution-scenarios	[WHY]	Hypothetical future stress vectors and how the design absorbs them
paradigm-rationale	[WHY]	Why FP/OOP was selected; comparison vs the alternative for this domain
reuse-analysis-deep-dive	[WHY]	Per-row justification for every EXTEND vs CREATE NEW decision in the Reuse table
c4-component-diagrams	[HOW]	Component-level C4 diagrams for complex subsystems (Mermaid)
expansion-catalog-rationale	[WHY]	Why this set of expansions, why these defaults, why D10 enforces one-line descriptions

Density resolution (per D12)

Call resolve_density(global_config) from scripts/shared/density_config.py after reading ~/.nwave/global-config.json (missing/malformed = empty dict). Returns mode ("lean" | "full") + expansion_prompt ("ask" | "always-skip" | "always-expand" | "smart") per the D12 cascade (resolver-internal, DDD-5 — do NOT replicate locally). Branch on density.mode for what to emit; branch on density.expansion_prompt at wave end for menu behaviour. Full cascade detail, branch semantics, ad-hoc override workflow: nWave/skills/nw-density-resolution-contract/SKILL.md.

Telemetry (per D4 + DDD-6)

Every expansion choice emits a DocumentationDensityEvent (dataclass at src/des/domain/telemetry/documentation_density_event.py) via event.to_audit_event() → JsonlAuditLogWriter().log_event(...). Schema fields per D4: feature_id, wave, expansion_id, choice, timestamp. For this wave the schema declares "wave": "DESIGN". Use helper scripts/shared/telemetry.py:write_density_event(...) — do NOT write JSONL directly.

Wave-specific signal: DEVOPS/DISTILL consuming a lean DESIGN feature-delta — downstream --expand requests for trade-off or evolution scenarios indicate the [REF] baseline was insufficient. Full emission rules: nWave/skills/nw-density-resolution-contract/SKILL.md.

Prior Wave Consultation

Before beginning DESIGN work, read SSOT and prior wave artifacts in this order:

1. Read SSOT architecture (if docs/product/ exists) — read docs/product/architecture/brief.md (extend, not recreate), docs/product/architecture/adr-*.md (existing decisions), docs/product/journeys/{name}.yaml (journey schema for port identification). Gate: all existing files read or confirmed missing.
2. Read DISCUSS artifacts (primary input) — read from docs/feature/{feature-id}/discuss/: wave-decisions.md (decision summary), user-stories.md (scope, requirements, acceptance criteria), story-map.md (walking skeleton and release slicing), outcome-kpis.md (quality attributes). Gate: all four files read or confirmed missing.
3. Read SPIKE findings (if spike was run) — read from docs/feature/{feature-id}/spike/: findings.md (validated assumptions, performance measurements, what didn't work). This informs your architecture constraints. Gate: file read if present, marked as not found if absent.
4. Output confirmation checklist — after reading, output ✓ {file} for each read, ⊘ {file} (not found) for each missing. Gate: checklist produced before any architecture work begins.
5. Check for contradictions — identify any DESIGN decisions that would contradict DISCUSS requirements or SPIKE findings. Flag contradictions and resolve with user before proceeding. Example: DISCUSS requires "real-time updates" but DESIGN chooses batch processing; or SPIKE found performance budget can't be met. Gate: zero unresolved contradictions.
6. Migration gate check — if docs/product/ does not exist but docs/feature/ has existing features, STOP. Guide the user to docs/guides/migrating-to-ssot-model/README.md. If greenfield, proceed — DESIGN will bootstrap docs/product/architecture/. Gate: migration status confirmed.

Note: DISCOVER evidence is already synthesized into DISCUSS — read DISCOVER only if wave-decisions.md flags something architecturally significant.

Document Update (Back-Propagation)

When DESIGN decisions change assumptions from prior waves:

1. Document the change — add a ## Changed Assumptions section at the end of the affected DESIGN artifact. Gate: section present in artifact.
2. Reference the original — quote the original assumption from the prior-wave document, with file path. Gate: original quoted verbatim with source.
3. State the new assumption — write the replacement assumption and its rationale. Gate: new assumption and rationale present.
4. Propagate upstream if needed — if architecture constraints require changes to user stories or acceptance criteria, write them to docs/feature/{feature-id}/design/upstream-changes.md for the product owner to review. Gate: upstream-changes.md created if any story/criteria changes needed.

Discovery Flow

Architecture decisions are driven by quality attributes, not pattern shopping. Execute these steps in order:

1. Understand the Problem — review JTBD artifacts from DISCUSS. Ask: What are we building? For whom? Which quality attributes matter most? (scalability|maintainability|testability|time-to-market|fault tolerance|auditability). Gate: quality attribute priorities ranked.

2. Understand Constraints — ask: Team size/experience? Timeline? Existing systems to integrate? Regulatory requirements? Operational maturity (CI/CD, monitoring)? Gate: constraints list documented.

3. Map Team Structure (Conway's Law) — ask: How many teams? Communication patterns? Does proposed architecture match org chart? Gate: team-architecture alignment confirmed.

4. Select Development Paradigm — identify primary language(s) from constraints, then: FP-native (Haskell|F#|Scala|Clojure|Elixir) → recommend Functional; OOP-native (Java|C#|Go) → recommend OOP; Multi-paradigm (TypeScript|Kotlin|Python|Rust|Swift) → present both, let user choose. After confirmation, ask user permission to write paradigm to project CLAUDE.md: FP: This project follows the **functional programming** paradigm. Use @nw-functional-software-crafter for implementation. OOP: This project follows the **object-oriented** paradigm. Use @nw-software-crafter for implementation. Default if user declines/unsure: OOP. Gate: paradigm selected and optionally written to CLAUDE.md.

5. Reuse Analysis (MANDATORY — RCA F-1 fix) — before designing ANY new component, search the existing codebase for components with overlapping responsibilities. For each overlap, decide "extend existing" or "justify new". Output a table:

   | Existing Component | File | Overlap | Decision | Justification |
   |-------------------|------|---------|----------|---------------|
   | WorkflowExecutor | src/des/application/zero_trust/workflow_executor.py | Phase iteration, gate eval | EXTEND | Adding dispatch branch is ~15 LOC vs 200 LOC new class |
   

   Rules:

   • If the design creates a new class that does something an existing class already does (iterate phases, evaluate gates, dispatch agents, handle retry), the default is EXTEND, not CREATE NEW.
   • CREATE NEW requires evidence that extending is impossible or creates unacceptable coupling (not just "it's complex").
   • "The existing class has too many dependencies" is NOT a valid justification — simplify the existing class instead (see F-4: strategy pattern extraction).
   • The reviewer MUST verify this table exists and challenge every "CREATE NEW" decision.
   • Gate: Reuse Analysis table present with zero unjustified CREATE NEW decisions.

6. Recommend Architecture Based on Drivers — recommend based on quality attribute priorities|constraints|paradigm from steps 1-5. Default: modular monolith with dependency inversion (ports-and-adapters). Overrides require evidence. If functional paradigm: apply types-first design, composition pipelines, pure core / effect shell, effect boundaries as ports, immutable state — in architecture document only, no code snippets. Gate: architecture pattern selected with written rationale.

Outcome Collision Check (per DISCUSS#D-5 grain)

Provenance: feature outcomes-registry — DISCUSS#D-2 (lean Tier-1 + Tier-2 default), D-5 (per-typed-contract grain), D-6 (gate-scoping: code-feature pipelines only).

Trigger: a new feature-delta has been emitted in DESIGN with a Reuse Analysis table. Run this check AFTER step 5 (Reuse Analysis) in the Discovery Flow and BEFORE producing the final architecture deliverables in step 7.

Skip when: the feature is methodology-only (skill propagation, prose changes, no new typed contract surface). Per D-6 gate-scoping, the outcomes registry tracks code-feature pipelines only.

Procedure:

1. Run the collision-check CLI against the freshly-emitted feature-delta:

   nwave-ai outcomes check-delta docs/feature/{feature-id}/feature-delta.md
   

2. Handle exit codes:
   • Exit 0 — no collisions detected. Proceed to step 7 (Produce Deliverables).
   • Exit 1 — one or more candidate outcomes overlap with existing OUT-N rows in docs/product/outcomes/registry.yaml. Review the reported OUT-ids. For each:
     • Genuine duplication: link the new candidate to the existing OUT-N via related: [OUT-N] in the registry, OR mark the existing OUT-N superseded_by: OUT-M if the new contract replaces it. Re-run check-delta to confirm.
     • False positive (Tier-1 keyword/shape match fired but Tier-2 disambiguation reveals the contracts are distinct): annotate the candidate's keywords in the registry to be more distinctive, then re-run.

The registry at docs/product/outcomes/registry.yaml is the SSOT for "what we promise the system does." Reuse Analysis (step 5) deduplicates within the codebase; the Outcome Collision Check deduplicates across the contract registry — they are complementary gates.

Gate: check-delta exits 0, OR every reported collision has been resolved (linked, superseded, or disambiguated) and the re-run exits 0, OR the feature is documented as methodology-only and the check is correctly skipped.

Rigor Profile Integration

Before dispatching the architect agent, read rigor config from .nwave/des-config.json (key: rigor). If absent, use standard defaults.

• agent_model: Pass as model parameter to Task tool. If "inherit", omit model (inherits from session).
• reviewer_model: If design review is performed, use this model for the reviewer agent. If "skip", skip design review.
• review_enabled: If false, skip post-design review step.

Structural-correctness reviewer never skips: rigor.reviewer_model: "skip" applies to scale-sensitive cost-driven reviewers (Eclipse / Architect / Forge here, plus their per-wave equivalents). The structural-correctness reviewer at the end of DISTILL (Sentinel / @nw-acceptance-designer-reviewer) ALWAYS dispatches — silent skip masks Gherkin antipatterns / boundary violations / contract drift, which is the bug class issue #52 fixed.

Interactive Decision Points

Decision 0: Design Scope (MANDATORY — do NOT skip)

Question: What are you designing?

You MUST ask this question before invoking any architect. Do NOT default to application scope. The answer determines WHICH agent to invoke.

Options:

1. System / infrastructure → invokes @nw-system-designer
2. Domain / bounded contexts → invokes @nw-ddd-architect
3. Application / components → invokes @nw-solution-architect
4. Full stack → invokes all three agents sequentially

Decision 1: Interaction Mode

Question: How do you want to work?

Options:

1. Guide me — the architect asks questions, you make decisions together
2. Propose — the architect reads your requirements and proposes 2-3 options with trade-offs

Agent Invocation

Architect Routing (based on Decision 0)

Decision 0	Agent	Focus
System / infrastructure	@nw-system-designer	Distributed architecture, scalability, caching, load balancing, message queues
Domain / bounded contexts	@nw-ddd-architect	DDD, aggregates, Event Modeling, event sourcing, context mapping
Application / components	@nw-solution-architect	Component boundaries, hexagonal architecture, tech stack, ADRs
Full stack	@nw-system-designer then @nw-ddd-architect then @nw-solution-architect	All three in sequence

Pass Decision 1 (guide/propose) to the invoked agent as the interaction mode.

All agents write to docs/product/architecture/ (SSOT). Each architect owns its section:

• @nw-system-designer writes ## System Architecture in brief.md
• @nw-ddd-architect writes ## Domain Model in brief.md
• @nw-solution-architect writes ## Application Architecture in brief.md

For Full stack mode, each agent reads the prior architect's output before starting its own work.

Agent Dispatch (after Decision 0 — no default)

Based on Decision 0 answer, invoke the corresponding agent. Do NOT default to application scope without asking.

System scope → @nw-system-designer Domain scope → @nw-ddd-architect Application scope → @nw-solution-architect Full stack → @nw-system-designer then @nw-ddd-architect then @nw-solution-architect

Execute *design-architecture for {feature-id}.

Context files: see Prior Wave Consultation above.

Configuration:

• model: rigor.agent_model (omit if "inherit")
• interaction_mode: {Decision 1: "guide" or "propose"}
• interactive: moderate
• output_format: markdown
• diagram_format: mermaid (C4)
• stress_analysis: {true if --residuality flag, false otherwise}

SKILL_LOADING: Read your skill files at ~/.claude/skills/nw-{skill-name}/SKILL.md. At Phase 4, always load: nw-architecture-patterns, nw-architectural-styles-tradeoffs. Do NOT load nw-roadmap-design during DESIGN wave -- roadmap creation belongs to the DELIVER wave (/nw-roadmap or /nw-deliver). Then follow your Skill Loading Strategy table for phase-specific skills.

Success Criteria

• Business drivers and constraints gathered before architecture selection
• Existing system analyzed before design (codebase search performed)
• Integration points with existing components documented
• Reuse Analysis table present with every overlapping component listed (HARD GATE — reviewer blocks without this)
• Architecture supports all business requirements
• Technology stack selected with clear rationale
• Development paradigm selected and (optionally) written to project CLAUDE.md
• Component boundaries defined with dependency-inversion compliance
• C4 System Context + Container diagrams produced (Mermaid)
• ADRs written with alternatives considered
• Per-wave peer review (OPTIONAL — invoke /nw-review nw-solution-architect-reviewer only on trigger: contested ADR, novel pattern, performance-budget unverified by spike, security boundary change. Default: skip. Mandatory consolidated review fires at end of DISTILL covering all 4 waves in parallel.)
• Handoff accepted by nw-platform-architect (DEVOPS wave)

Next Wave

Handoff To: nw-platform-architect (DEVOPS wave) Deliverables: See Morgan's handoff package specification in agent file

Wave Decisions Summary

Before completing DESIGN, produce docs/feature/{feature-id}/design/wave-decisions.md:

# DESIGN Decisions — {feature-id}

## Key Decisions
- [D1] {decision}: {rationale} (see: {source-file})

## Architecture Summary
- Pattern: {e.g., modular monolith with ports-and-adapters}
- Paradigm: {OOP|FP}
- Key components: {list top-level components}

## Reuse Analysis
| Existing Component | File | Overlap | Decision | Justification |
|-------------------|------|---------|----------|---------------|
| {component} | {path} | {what overlaps} | EXTEND/CREATE NEW | {evidence} |

## Technology Stack
- {language/framework}: {rationale}

## Constraints Established
- {architectural constraint}

## Upstream Changes
- {any DISCUSS assumptions changed, with rationale}

This summary enables DEVOPS and DISTILL to quickly assess architecture decisions without reading all DESIGN files.

Outputs

Single narrative file: docs/feature/{feature-id}/feature-delta.md — DDD list, component decomposition, driving/driven ports, technology choices, decisions table, reuse analysis, open questions all become ## Wave: DESIGN / [REF|WHY|HOW] <Section> headings.

Machine artifacts: none unique to feature dir (the feature-delta.md IS the artifact; SSOT writes carry the architectural payload).

SSOT updates (per Recommendation 3 / back-propagation contract — DESIGN is the primary SSOT integrator):

• docs/product/architecture/brief.md — created or updated. Each architect owns its section: ## System Architecture (nw-system-designer), ## Domain Model (nw-ddd-architect), ## Application Architecture (nw-solution-architect)
• docs/product/architecture/adr-*.md — one ADR per significant architectural decision
• docs/product/architecture/c4-diagrams.md — current component topology if separate from brief

Optional (project-root, not feature-dir): CLAUDE.md ## Development Paradigm section.

Legacy multi-file outputs (per-wave wave-decisions.md, architecture-design.md, etc. inside docs/feature/{id}/design/) are NOT produced — that content lives in feature-delta.md plus the SSOT integration above. Validator: scripts/validation/validate_feature_layout.py.