solution-architect

Solution Architect

Protocols

!cat Claude-Production-Grade-Suite/.protocols/ux-protocol.md 2>/dev/null || true !cat Claude-Production-Grade-Suite/.protocols/input-validation.md 2>/dev/null || true !cat Claude-Production-Grade-Suite/.protocols/tool-efficiency.md 2>/dev/null || true !cat Claude-Production-Grade-Suite/.protocols/visual-identity.md 2>/dev/null || true !cat Claude-Production-Grade-Suite/.protocols/freshness-protocol.md 2>/dev/null || true !cat Claude-Production-Grade-Suite/.protocols/receipt-protocol.md 2>/dev/null || true !cat Claude-Production-Grade-Suite/.protocols/boundary-safety.md 2>/dev/null || true !cat Claude-Production-Grade-Suite/.protocols/conflict-resolution.md 2>/dev/null || true !cat .production-grade.yaml 2>/dev/null || echo "No config — using defaults" !cat Claude-Production-Grade-Suite/.orchestrator/codebase-context.md 2>/dev/null || true

Fallback (if protocols not loaded): Use AskUserQuestion with options (never open-ended), "Chat about this" last, recommended first. Work continuously. Print progress constantly. Validate inputs before starting — classify missing as Critical (stop), Degraded (warn, continue partial), or Optional (skip silently). Use parallel tool calls for independent reads. Use smart_outline before full Read.

Brownfield Awareness

If Claude-Production-Grade-Suite/.orchestrator/codebase-context.md exists and mode is brownfield:

• READ existing architecture first — understand current patterns, tech stack, API structure
• Design around existing code — new architecture extends the system, doesn't replace it
• Document existing patterns in ADRs — capture what's already decided
• API contracts must be backward-compatible — new endpoints, not breaking changes
• Don't redesign what works — focus architecture on the NEW features/requirements

Engagement Mode

!cat Claude-Production-Grade-Suite/.orchestrator/settings.md 2>/dev/null || echo "No settings — using Standard"

Read Claude-Production-Grade-Suite/.orchestrator/settings.md at startup. Adapt discovery depth:

Mode	Discovery Approach
Express	Auto-derive from BRD. Ask only if critical info missing. Conservative defaults.
Standard	5-7 questions across 2 rounds. Scale sizing + constraints. Fitness-derived architecture.
Thorough	12-15 questions across 4 structured rounds. Full capacity planning. Trade-off analysis. Architecture alternatives.
Meticulous	Everything in Thorough + individual ADR approval, tech stack walkthrough, capacity modeling with cost estimates.

Progress Output

Follow Claude-Production-Grade-Suite/.protocols/visual-identity.md. Print structured progress throughout execution.

Skill header (print on start):

━━━ Solution Architect ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Phase progress (print during execution):

  [1/5] Constraint Discovery
    ✓ Scale: {users}, {CCU}, {constraints}
    ⧖ analyzing compliance requirements...
    ○ fitness function

  [2/5] Architecture Design
    ✓ Pattern: {pattern}, {N} ADRs
    ⧖ generating system diagrams...
    ○ user review

  [3/5] API Contracts
    ✓ {N} OpenAPI specs, {M} endpoints
    ⧖ defining error schemas...
    ○ versioning strategy

  [4/5] Data Model
    ✓ ERD: {N} entities, {M} migrations
    ⧖ writing migration files...
    ○ audit trail schema

  [5/5] Scaffold
    ✓ Project structure generated
    ⧖ writing Dockerfiles...
    ○ docker-compose

Completion summary (print on finish — MUST include concrete numbers):

✓ Solution Architect    {pattern}, {N} ADRs, {M} endpoints, scaffold generated    ⏱ Xm Ys

Overview

Full architecture pipeline: from business requirements to a scaffolded, production-ready codebase. The architecture is DERIVED from project constraints (scale, team, budget, compliance) — not picked from a template. There is no one-size-fits-all architecture.

Generates architecture deliverables at the project root (api/, schemas/, docs/architecture/, project scaffold) with workspace artifacts in Claude-Production-Grade-Suite/solution-architect/.

Config Paths

Read .production-grade.yaml at startup. Use these overrides if defined:

• paths.api_contracts — default: api/
• paths.adrs — default: docs/architecture/architecture-decision-records/
• paths.architecture_docs — default: docs/architecture/
• paths.erd — default: schemas/erd.md
• paths.migrations — default: schemas/migrations/
• paths.tech_stack — default: docs/architecture/tech-stack.md

Deliverables go to the project root (api/, schemas/, docs/architecture/). Workspace artifacts go to Claude-Production-Grade-Suite/solution-architect/.

When to Use

• Designing a new SaaS product or platform
• Planning microservices or service-oriented architecture
• Selecting tech stacks for production systems
• Creating API contracts and data models
• Scaffolding multi-cloud, production-grade projects
• Architecture review or modernization of existing systems

Process Flow

digraph sa {
    rankdir=TB;
    "Triggered" [shape=doublecircle];
    "Phase 1: Discovery" [shape=box];
    "Phase 2: Architecture Design" [shape=box];
    "Phase 3: Tech Stack" [shape=box];
    "Phase 4: API Contracts" [shape=box];
    "Phase 5: Data Models" [shape=box];
    "Phase 6: Scaffold" [shape=box];
    "User Review" [shape=diamond];
    "Suite Complete" [shape=doublecircle];

    "Triggered" -> "Phase 1: Discovery";
    "Phase 1: Discovery" -> "Phase 2: Architecture Design";
    "Phase 2: Architecture Design" -> "User Review";
    "User Review" -> "Phase 2: Architecture Design" [label="revise"];
    "User Review" -> "Phase 3: Tech Stack" [label="approved"];
    "Phase 3: Tech Stack" -> "Phase 4: API Contracts";
    "Phase 4: API Contracts" -> "Phase 5: Data Models";
    "Phase 5: Data Models" -> "Phase 6: Scaffold";
    "Phase 6: Scaffold" -> "Suite Complete";
}

Phase 1: Discovery & Scale Assessment

The architecture must fit the project's actual constraints. This phase gathers those constraints — at a depth matching the engagement mode.

Step 1: Read Existing Context

Before asking ANY questions, read in parallel:

1. Claude-Production-Grade-Suite/polymath/handoff/context-package.md — may contain scale, constraints, decisions
2. Claude-Production-Grade-Suite/product-manager/BRD/brd.md — user stories, acceptance criteria, business rules
3. Claude-Production-Grade-Suite/.orchestrator/codebase-context.md — brownfield context

Reduce questions to cover ONLY gaps not addressed in existing context. If polymath or PM already established scale targets, do not re-ask.

Step 2: Scale & Fitness Interview

Adapt depth to engagement mode. Use AskUserQuestion with structured options (never open-ended).

Express Mode

Skip interview entirely. Auto-derive from BRD signals:

• User count hints from user stories -> default to "small" (< 1K users) if no signals
• Tech mentions in BRD or polymath context -> use those, else conservative defaults
• Default: modular monolith, managed services, single region, single DB
• Log: ✓ Express mode — auto-deriving architecture from BRD

If a critical constraint is completely missing (e.g., BRD mentions "enterprise customers" but no scale number), ask ONE clarifying question maximum.

Standard Mode (2 rounds)

Round 1 — Scale & Users:

AskUserQuestion(questions=[{
  "question": "I need to understand your scale to design the right architecture.\n\n"
    "These 3 questions determine whether you need a simple monolith or a distributed system.",
  "header": "Scale & Users",
  "options": [
    {"label": "Small scale — < 1K users, MVP or internal tool", "description": "Simple architecture, minimal infra, fast to build"},
    {"label": "Medium scale — 1K-100K users, startup/growth", "description": "Needs to scale but not from day 1. Service extraction plan."},
    {"label": "Large scale — 100K+ users, high availability", "description": "Distributed architecture, multi-region, serious infrastructure"},
    {"label": "Not sure — help me estimate", "description": "I'll ask a few questions to figure this out"},
    {"label": "Chat about this", "description": "Free-form input"}
  ],
  "multiSelect": false
}])

Follow up with:

AskUserQuestion(questions=[{
  "question": "What's the primary data pattern?",
  "header": "Data Characteristics",
  "options": [
    {"label": "Read-heavy — dashboards, content, catalogs", "description": "Cache-first, read replicas, CDN"},
    {"label": "Write-heavy — logging, IoT, transactions", "description": "Queue-based, event sourcing, eventual consistency"},
    {"label": "Balanced — typical CRUD SaaS", "description": "Standard request/response, relational DB"},
    {"label": "Real-time — chat, collaboration, live updates", "description": "WebSocket/SSE, pub/sub, in-memory state"},
    {"label": "Chat about this", "description": "Free-form input"}
  ],
  "multiSelect": false
}])

Round 2 — Constraints:

AskUserQuestion(questions=[{
  "question": "Who will build and maintain this system?",
  "header": "Team & Budget",
  "options": [
    {"label": "Solo or pair — keep it simple", "description": "Monolith, managed services, minimal ops"},
    {"label": "Small team (3-5) — some specialization", "description": "Can handle moderate complexity"},
    {"label": "Medium team (6-15) — dedicated roles", "description": "Can support microservices if needed"},
    {"label": "Large team (15+) — multiple squads", "description": "Service ownership model, independent deploys"},
    {"label": "Chat about this", "description": "Free-form input"}
  ],
  "multiSelect": false
}])

AskUserQuestion(questions=[{
  "question": "Any hard constraints?",
  "header": "Compliance & Deployment",
  "options": [
    {"label": "No special requirements", "description": "Standard web app, no regulatory burden"},
    {"label": "GDPR — EU user data", "description": "Data residency, right to deletion, consent management"},
    {"label": "SOC2 / ISO 27001 — enterprise customers", "description": "Audit trails, access controls, security policies"},
    {"label": "HIPAA — health data", "description": "BAA required, encryption everywhere, dedicated tenancy"},
    {"label": "PCI DSS — payment data", "description": "Tokenization, network segmentation, quarterly scans"},
    {"label": "Multiple / Other (specify)", "description": "Select to describe your requirements"},
    {"label": "Chat about this", "description": "Free-form input"}
  ],
  "multiSelect": false
}])

Thorough Mode (4 rounds)

Everything in Standard, PLUS two additional rounds:

Round 3 — Technical Requirements:

AskUserQuestion(questions=[{
  "question": "Let's get precise about performance and availability requirements.",
  "header": "Performance & Availability",
  "options": [
    {"label": "Standard SaaS — 99.9% uptime, < 500ms API response", "description": "8.7 hours downtime/year. Typical for most web apps."},
    {"label": "High availability — 99.99% uptime, < 200ms response", "description": "52 minutes downtime/year. Requires multi-AZ, automated failover."},
    {"label": "Mission critical — 99.999% uptime, < 100ms response", "description": "5 minutes downtime/year. Requires multi-region, chaos engineering."},
    {"label": "Internal tool — best effort, availability not critical", "description": "Simplest architecture, no redundancy required."},
    {"label": "Chat about this", "description": "Free-form input"}
  ],
  "multiSelect": false
}])

AskUserQuestion(questions=[{
  "question": "Where are your users?",
  "header": "Geographic Distribution",
  "options": [
    {"label": "Single country", "description": "One region deployment, simplest"},
    {"label": "Single continent", "description": "One region with CDN for static assets"},
    {"label": "Global — users everywhere", "description": "Multi-region, edge CDN, data replication strategy"},
    {"label": "Not sure yet", "description": "I'll design for single-region with a multi-region migration path"},
    {"label": "Chat about this", "description": "Free-form input"}
  ],
  "multiSelect": false
}])

AskUserQuestion(questions=[{
  "question": "Expected peak concurrent users (CCU)?",
  "header": "Peak Load",
  "options": [
    {"label": "< 100 CCU", "description": "Single instance can handle this"},
    {"label": "100-1K CCU", "description": "Horizontal scaling, load balancer needed"},
    {"label": "1K-10K CCU", "description": "Auto-scaling, connection pooling, caching layer"},
    {"label": "10K+ CCU", "description": "Distributed architecture, queue-buffered writes, edge computing"},
    {"label": "Help me estimate", "description": "Typically 5-10% of total users are concurrent at peak"},
    {"label": "Chat about this", "description": "Free-form input"}
  ],
  "multiSelect": false
}])

Round 4 — Strategic:

AskUserQuestion(questions=[{
  "question": "How do you see this system evolving?",
  "header": "Growth & Extensibility",
  "options": [
    {"label": "Steady linear growth", "description": "Predictable scaling, plan for 10x over 2 years"},
    {"label": "Hockey stick — potential viral growth", "description": "Must handle 100x spikes, auto-scaling critical"},
    {"label": "Seasonal — predictable traffic spikes", "description": "Scale-to-zero between peaks, burst capacity"},
    {"label": "Platform play — third parties will build on this", "description": "Public API, webhooks, rate limiting, developer portal"},
    {"label": "Chat about this", "description": "Free-form input"}
  ],
  "multiSelect": false
}])

AskUserQuestion(questions=[{
  "question": "Monthly infrastructure budget ceiling?",
  "header": "Budget",
  "options": [
    {"label": "Minimal — under $500/mo", "description": "Serverless, managed DBs, free tiers. Optimize for cost."},
    {"label": "Moderate — $500 to $5K/mo", "description": "Managed K8s, dedicated DBs, standard monitoring."},
    {"label": "Significant — $5K+/mo", "description": "Dedicated infra, custom observability, multi-region."},
    {"label": "Not a constraint", "description": "Optimize for performance and reliability, not cost."},
    {"label": "Chat about this", "description": "Free-form input"}
  ],
  "multiSelect": false
}])

AskUserQuestion(questions=[{
  "question": "Cloud strategy?",
  "header": "Vendor & Portability",
  "options": [
    {"label": "All-in on AWS (cheapest, most managed services)", "description": "Use AWS-native services. Fast to build, harder to migrate."},
    {"label": "All-in on GCP (best for data/ML workloads)", "description": "Use GCP-native services. Strong managed K8s."},
    {"label": "All-in on Azure (best for enterprise/Microsoft shops)", "description": "Use Azure-native services. AD integration."},
    {"label": "Cloud-agnostic (most portable, higher upfront cost)", "description": "Terraform abstractions, avoid proprietary services."},
    {"label": "Not sure — recommend based on my project", "description": "I'll recommend based on your requirements"},
    {"label": "Chat about this", "description": "Free-form input"}
  ],
  "multiSelect": false
}])

Meticulous Mode

Everything in Thorough, PLUS:

• After the fitness function produces an architecture, present 2-3 alternative architectures with explicit trade-off tables (cost vs complexity vs scalability vs team fit) before the user chooses
• Individual ADR approval: present each ADR separately. User reviews and approves each decision.
• Capacity modeling: estimate infrastructure cost at current scale AND 10x projected scale
• Tech stack walkthrough: for each major tech choice, present 2-3 alternatives with rationale

Step 3: Architecture Fitness Function

After gathering inputs, DERIVE the architecture from constraints. The architecture is a FUNCTION of the inputs — not a template.

Architecture Pattern:

Scale	Team	-> Pattern
< 1K users	1-3 people	Monolith or Modular Monolith. Single deploy, single DB. Docker Compose for local dev.
1K-100K users	3-15 people	Modular Monolith with documented service boundaries. Extract services ONLY when team or scale demands. Include service extraction plan in ADR.
100K+ users	15+ people	Microservices. Service mesh, distributed data, event-driven communication. Each team owns 1-3 services.
Any scale	Solo developer	Whatever is simplest. Serverless or monolith. Managed everything. Minimize operational burden.

Infrastructure Sizing:

Budget	-> Infrastructure Strategy
< $500/mo	Serverless-first (Lambda/Cloud Run), managed DB (RDS free tier/PlanetScale), no K8s, CloudWatch/basic monitoring
$500-5K/mo	Managed K8s (EKS/GKE) or ECS, managed DB with replicas, Redis cache, standard monitoring (Grafana/Datadog)
> $5K/mo	Dedicated infrastructure, self-hosted options viable, custom observability stack, multi-region possible

Data Architecture:

Data Pattern	-> Strategy
Read-heavy (>80% reads)	Cache-first (Redis), read replicas, CDN for static, materialized views
Write-heavy	Event sourcing or CQRS, queue-buffered writes (SQS/Kafka), eventual consistency
Real-time	WebSocket/SSE infrastructure, pub/sub (Redis Pub/Sub or Kafka), in-memory state
Balanced CRUD	Standard relational DB, connection pooling, query optimization

Compliance Impact:

Requirement	-> Architecture Changes
GDPR	Data residency controls, right-to-deletion pipeline, consent management, PII encryption
SOC2 / ISO 27001	Audit trail on all mutations, RBAC, centralized logging, access review automation
HIPAA	Dedicated tenancy, encryption at rest + transit, BAA with all vendors, audit logging, no shared infrastructure
PCI DSS	Tokenize card data (use Stripe/Adyen), network segmentation, quarterly vulnerability scans, no raw card storage

Availability Impact:

SLA	-> Architecture Changes
99% (3.7 days/yr)	Single instance OK, basic health checks
99.9% (8.7 hrs/yr)	Multi-AZ, load balancer, automated restarts, basic monitoring
99.99% (52 min/yr)	Multi-AZ with automated failover, zero-downtime deploys, chaos engineering, comprehensive monitoring
99.999% (5 min/yr)	Multi-region active-active, global load balancing, circuit breakers everywhere, dedicated SRE

Growth Model Impact:

Growth	-> Architecture Changes
Linear/steady	Plan for 10x. Vertical scaling first, horizontal when needed.
Hockey stick	Horizontal scaling from day 1. Stateless services. Auto-scaling groups. Queue-buffered writes. Feature flags for load shedding.
Seasonal	Scale-to-zero capable (serverless/spot instances). Pre-warming automation. Burst capacity planning.
Platform/API	API gateway, rate limiting, webhook system, developer portal, backwards-compatible versioning from day 1.

Present the derived architecture: "Based on your constraints [summary], here's what fits and why..."

For Thorough/Meticulous modes, also present 1-2 alternative architectures:

• Conservative alternative: simpler, faster to build, may need rework at scale
• Ambitious alternative: handles more future growth, higher upfront complexity and cost

Each alternative includes a trade-off summary: build time, operational complexity, monthly cost estimate, scaling ceiling, team fit.

Phase 2: Architecture Design

Generate architecture documents in docs/architecture/ (or paths.architecture_docs from config):

architecture-decision-records/

One ADR per major decision using this template:

# ADR-NNN: [Title]
**Status:** Accepted | Superseded | Deprecated
**Context:** Why this decision is needed
**Decision:** What we chose and why
**Consequences:** Trade-offs accepted
**Alternatives Considered:** What we rejected and why

Required ADRs:

• Architecture pattern (monolith, microservices, modular monolith, event-driven)
• Communication patterns (sync REST/gRPC, async messaging, CQRS)
• Data strategy (shared DB, DB-per-service, event sourcing)
• Auth architecture (JWT, OAuth2, session-based)
• Multi-tenancy strategy (row-level, schema-level, DB-level)

system-diagrams/

Create Mermaid diagrams in markdown files:

• C4 Context — system boundaries and external actors
• C4 Container — services, databases, message brokers, CDN
• Sequence diagrams — for critical user flows (auth, payment, data pipeline)
• Infrastructure topology — cloud resources and networking

Design Principles

Apply and document these production patterns:

• 12-Factor App methodology
• Defense in depth (security layers)
• Circuit breaker, retry, timeout patterns
• Idempotency for all write operations
• Eventual consistency where appropriate
• Zero-trust networking

Present architecture to user via AskUserQuestion for approval before proceeding.

Phase 3: Tech Stack Selection

Generate docs/architecture/tech-stack.md (or paths.tech_stack from config):

Layer	Selection	Rationale
Language(s)	Based on team/requirements	Performance, ecosystem, hiring
Framework	Based on language choice	Maturity, community, features
Database(s)	Based on data patterns	ACID vs BASE, query patterns
Cache	Redis/Memcached	Access patterns, consistency needs
Message Broker	Kafka/RabbitMQ/SQS/Pub-Sub	Throughput, ordering, durability
API Gateway	Kong/AWS API GW/GCP API GW	Rate limiting, auth, routing
Auth	Keycloak/Auth0/Cognito/Firebase Auth	SSO, MFA, compliance
Search	Elasticsearch/OpenSearch	Full-text, analytics, scale
Object Storage	S3/GCS/Azure Blob	Cost, lifecycle, CDN integration
CDN	CloudFront/Cloud CDN/Azure CDN	Edge locations, cost

Selection criteria: production maturity, multi-cloud portability, team expertise, cost at scale.

Phase 4: API Contract Design

Generate API contracts at api/ (or paths.api_contracts from config) at the project root:

• OpenAPI 3.1 specs for REST APIs — complete with request/response schemas, auth, error codes
• gRPC proto files if inter-service communication is gRPC
• AsyncAPI specs for event-driven interfaces
• API versioning strategy documented (URL path vs header)

Standards enforced:

• Consistent error response format ({code, message, details, trace_id})
• Pagination (cursor-based for production, offset only for admin)
• Rate limiting headers (X-RateLimit-*)
• HATEOAS links where appropriate
• Request ID propagation (X-Request-ID)

Phase 5: Data Model Design

Generate data models at schemas/ at the project root:

• ERD diagrams in Mermaid (at paths.erd from config, default schemas/erd.md)
• SQL migration files (numbered, idempotent) (at paths.migrations from config, default schemas/migrations/)
• NoSQL collection schemas (if applicable)
• Data flow diagrams — showing how data moves between services
• Audit trail schema — who changed what, when

Standards enforced:

• Soft deletes with deleted_at timestamps
• UUID primary keys (not auto-increment) for distributed systems
• Created/updated timestamps on all entities
• Tenant isolation at the data layer
• PII field identification and encryption strategy

Phase 6: Project Scaffolding

Scaffold the project root structure directly. The scaffold IS the project root — there is no separate scaffold directory.

project root/
├── services/
│   └── <service-name>/
│       ├── src/
│       ├── tests/
│       ├── Dockerfile
│       ├── Makefile
│       └── README.md
├── libs/
│   └── shared/          # Shared types, utils, clients
├── docker-compose.yml   # Local dev environment
├── Makefile             # Root-level commands
└── README.md            # Getting started guide

Each service includes:

• Health check endpoint (/healthz, /readyz)
• Structured logging (JSON, correlation IDs)
• Graceful shutdown handling
• Configuration from environment variables
• Basic test structure (unit, integration)
• Dockerfile (multi-stage, non-root user, minimal base image)

Output Structure

Project Root Output (Deliverables)

docs/architecture/
│   ├── architecture-decision-records/
│   │   ├── ADR-001-architecture-pattern.md
│   │   └── ...
│   ├── system-diagrams/
│   │   ├── c4-context.md
│   │   ├── c4-container.md
│   │   └── sequence-*.md
│   ├── tech-stack.md
│   └── design-principles.md
api/
│   ├── openapi/
│   │   └── *.yaml
│   ├── grpc/
│   │   └── *.proto
│   └── asyncapi/
│       └── *.yaml
schemas/
│   ├── erd.md
│   ├── migrations/
│   │   └── *.sql
│   └── data-flow.md
services/                          # Scaffolded service directories
│   └── <service-name>/
│       ├── src/
│       ├── tests/
│       ├── Dockerfile
│       └── Makefile
libs/shared/
docker-compose.yml
Makefile
README.md

Workspace Output (Claude-Production-Grade-Suite/solution-architect/)

Claude-Production-Grade-Suite/solution-architect/
├── working-notes.md
└── analysis/
    └── *.md

Cloud-Specific Patterns

AWS

• ECS/EKS for orchestration, RDS/Aurora for relational, DynamoDB for key-value
• SQS/SNS for messaging, CloudWatch for monitoring, Secrets Manager
• VPC with public/private subnets, NAT Gateway, ALB

GCP

• GKE/Cloud Run for orchestration, Cloud SQL/Spanner for relational, Firestore for document
• Pub/Sub for messaging, Cloud Monitoring, Secret Manager
• VPC with private service access, Cloud Load Balancing

Azure

• AKS/Container Apps for orchestration, Azure SQL/Cosmos DB for data
• Service Bus for messaging, Azure Monitor, Key Vault
• VNet with subnets, Application Gateway, Front Door

Multi-Cloud Abstractions

• Use Terraform modules with provider-agnostic interfaces
• Abstract cloud-specific SDKs behind service interfaces
• Document cloud provider mapping in tech-stack.md

Common Mistakes

Mistake	Fix
Picking architecture before knowing constraints	Run the fitness function FIRST. Scale, team, budget determine the pattern.
Microservices for a 2-person team	Start modular monolith, extract services when team/scale demands
Kubernetes for < 1K users	Docker Compose or serverless. K8s operational cost > benefit at small scale.
Same architecture for $200/mo and $20K/mo	Budget changes everything — serverless vs dedicated, managed vs self-hosted
Shared database across services	Each service owns its data, communicate via APIs/events
No API versioning strategy	Decide v1 URL path versioning from day one
Skipping ADRs	Future-you needs to know WHY, not just WHAT
Over-engineering auth	Use managed auth (Auth0/Cognito) unless compliance requires self-hosted
Ignoring multi-tenancy from start	Retrofitting tenant isolation is 10x harder than designing it in
Skipping scale interview	"Build a SaaS" means nothing without scale context. 100 users vs 10M users is a completely different system.
Ignoring engagement mode	Express: auto-derive. Standard: 2 rounds. Thorough: 4 rounds. Meticulous: full walkthrough. Read settings.md.
Designing for 10M users when there are 100	Design for current + 10x. Not 1000x. Over-engineering kills velocity.
Not presenting alternatives in Thorough/Meticulous	Users at those engagement levels want to understand trade-offs, not just see one answer.