system-design（系统设计）

System Design

Generate comprehensive Technical Architecture Documents with modular design for startups.

Subagent Architecture

This skill uses parallel research agents with upfront content extraction. Pattern: D (Research+Synthesis) + E (Staged Pipeline).

Agents

Research Rounds (5 Parallel)

• Round 1: Technology Stack validation (React, Node.js, PostgreSQL, Elasticsearch)
• Round 2: Infrastructure validation (Vercel, AWS, CDN, cost estimation)
• Round 3: Security review (auth, encryption, compliance, API security)
• Round 4: Risk assessment (bottlenecks, vendor lock-in, team gaps)
• Round 5: Holistic review (PRD alignment, team capability, quick wins)

Parallelization Strategy

• PRD Content: Extracted once by prd-reader, stays out of main context
• Research Independence: Each round researches conceptually different angle (tech vs. infra vs. security)
• Reasoning Isolation: Parallel rounds keep each area's reasoning isolated, prevent groupthink
• Note: Research rounds are conceptual reasoning, not data fetching — parallel rounds won't produce fundamentally different info, but isolation improves quality

Result: All 5 rounds complete concurrently, tad-writer synthesizes outputs into unified TAD.

Environment Check

Before executing:

1. Verify prd.md exists in project directory
2. Check for supporting docs (idea.md, validate.md) if available
3. Confirm WebSearch and WebFetch tools available for research
4. Verify write permissions to project root for tad.md creation
5. Ensure git access for final commit

Repo Sync Before Edits (mandatory)

Before creating/updating/deleting files in an existing repository, sync the current branch with remote:

branch="$(git rev-parse --abbrev-ref HEAD)"
git fetch origin
git pull --rebase origin "$branch"

If the working tree is not clean, stash first, sync, then restore:

git stash push -u -m "pre-sync"
branch="$(git rev-parse --abbrev-ref HEAD)"
git fetch origin && git pull --rebase origin "$branch"
git stash pop

If origin is missing, pull is unavailable, or rebase/stash conflicts occur, stop and ask the user before continuing.

Input

Project folder path in $ARGUMENTS containing:

• prd.md - Product requirements (required)
• idea.md, validate.md - Additional context (optional)

Workflow

Phase 1: Setup & Validation

1. Verify prd.md exists
2. Read supporting docs if present
3. Read references/tech-stack.md for technology recommendations
4. Backup existing tad.md if present

Phase 2: Extract Context

From PRD extract:

• Product name and vision
• Core features and requirements
• User flows
• Non-functional requirements
• Third-party integrations
• Analytics requirements

Phase 3: Clarify Architecture

Ask user (if not clear):

Phase 4: Research & Validation

Conduct 5 research rounds:

1. Technology Stack: Validate choices against industry standards
2. Infrastructure: Compare hosting for cost and scalability
3. Security: Review OWASP guidelines for chosen stack
4. Risk Assessment: Identify bottlenecks, vendor lock-in
5. Holistic Review: Ensure PRD alignment and startup feasibility

Phase 5: Generate TAD

Create tad.md with sections:

1. System Overview - Purpose, scope, PRD alignment
2. Architecture Diagram - Mermaid diagrams for system and flows
3. Technology Stack - Frontend, backend, database, infrastructure, DevOps
4. System Components - Modular design with interfaces and dependencies
5. Data Architecture - Schema, models, flows, storage
6. Infrastructure - Hosting, environments, scaling, CI/CD, monitoring
7. Security - Auth, authorization, data protection, API security
8. Performance - Targets, optimization strategies, caching
9. Development - Environment setup, project structure, testing, deployment
10. Risks - Risk matrix with mitigations
11. Appendix - Research insights, alternatives, costs, glossary

See references/tad-template.md for full template structure.

Phase 6: README Maintenance (ideas repo)

After writing tad.md, if the project folder is inside an ideas repo, update the repo README ideas table:

• Preferred: cd to repo root and run python3 scripts/update_readme_ideas_index.py (if it exists)
• Fallback: update README.md manually (ensure TAD status becomes ✅ for that idea)

Phase 7: Commit and push (mandatory)

• Commit immediately after updates.
• Push immediately to remote.
• If push is rejected: git fetch origin && git rebase origin/main && git push.

Do not ask for additional push permission once this skill is invoked.

Phase 8: Output

1. Write tad.md to project folder
2. Summarize architecture decisions
3. Highlight modular design benefits
4. List cost estimates by phase
5. Suggest next steps (setup dev environment, create tasks)

Reporting with GitHub links (mandatory)

When reporting completion, include:

• GitHub link to tad.md
• GitHub link to README.md when it was updated
• Commit hash

Link format (derive <owner>/<repo> from git remote get-url origin):

• https://github.com/<owner>/<repo>/blob/main/<relative-path>

Step Completion Reports

After completing each major step, output a status report in this format:

◆ [Step Name] ([step N of M] — [context])
··································································
  [Check 1]:          √ pass
  [Check 2]:          √ pass (note if relevant)
  [Check 3]:          × fail — [reason]
  [Check 4]:          √ pass
  [Criteria]:         √ N/M met
  ____________________________
  Result:             PASS | FAIL | PARTIAL

Adapt the check names to match what the step actually validates. Use √ for pass, × for fail, and — to add brief context. The "Criteria" line summarizes how many acceptance criteria were met. The "Result" line gives the overall verdict.

Phase-specific checks

Phase 1 — Setup

◆ Setup (step 1 of 8 — environment validation)
··································································
  PRD found:                    √ pass
  Context extracted:            √ pass (product + features + NFRs read)
  Architecture questions answered: √ pass (deployment, DB, auth, budget confirmed)
  ____________________________
  Result:             PASS | FAIL | PARTIAL

Phase 4 — Research

◆ Research (step 4 of 8 — validation rounds)
··································································
  5 parallel rounds completed:  √ pass
  Best practices gathered:      √ pass (tech, infra, security, risk, holistic)
  Patterns validated:           √ pass (OWASP, vendor lock-in, startup feasibility)
  ____________________________
  Result:             PASS | FAIL | PARTIAL

Phase 5 — Generation

◆ Generation (step 5 of 8 — TAD authoring)
··································································
  11 sections written:          √ pass
  tad.md created:               √ pass
  Diagrams included:            √ pass (mermaid architecture + flow diagrams)
  ____________________________
  Result:             PASS | FAIL | PARTIAL

Phase 8 — Output

◆ Output (step 8 of 8 — delivery)
··································································
  Summary presented:            √ pass (architecture decisions highlighted)
  README updated:               √ pass (TAD status ✅)
  Committed and pushed:         √ pass (commit hash: ...)
  ____________________________
  Result:             PASS | FAIL | PARTIAL

Modification Mode

For existing TAD changes:

1. Create timestamped backup
2. Ask what to modify (stack, infrastructure, security, data, scaling)
3. Apply changes preserving structure
4. Update revision history

Guidelines

• Practical: Implementable solutions for startups
• Cost-conscious: Consider budget implications
• Modular: Emphasize separation of concerns
• Specific: Concrete technology choices
• Visual: Include mermaid diagrams