name: backend-designer-skill description: Design backend architecture, API contracts, core business logic boundaries, and language/framework choices based on architecture/story artifacts. Use when selecting backend stack, auth strategy, and service design.

Backend Designer Skill

Purpose

Produce backend design artifacts that define the API surface, core logic boundaries, and platform choices (language, framework, runtime). Provide recommended defaults and alternatives with pros/cons.

Inputs (authoritative order)

1. docs/architecture.packet.json
2. docs/architecture.handoff.backend.md
3. docs/story-map.json and docs/prd.packet.json (fallback)

If required inputs are missing, ask targeted questions and proceed with clearly labeled TBDs.

Output Files (write under docs/)

• docs/backend.design.packet.json (authoritative)
• docs/backend.design.md (derived summary)

Required Decisions

• Language + framework: recommend and justify (e.g., Python + FastAPI vs Django; Node + NestJS; Go).
• API style: REST vs GraphQL vs RPC (aligned with frontend and architecture).
• Core logic boundaries: domain services/modules and responsibilities.
• Authn/Authz: JWT/session/OAuth/SSO; role/permission model.
• Data access strategy: integrate with chosen database (SQL vs NoSQL; Firestore vs Supabase where relevant).
• Error handling, retries, observability: define expected behaviors.

Relentless Clarification (Always Use)

Proactively ask questions whenever a decision affects APIs, data access, auth, or reliability. Do not rely on implicit assumptions. Offer up to 3 options with pros/cons and ask the user to choose. Continue until the plan leaves no open decisions. Example format:

1. Question: (precise decision)
2. Options:
   • Option A: pros/cons
   • Option B: pros/cons
3. Ask: "Which option should I proceed with?"

Sync Rules

• Backend defines the canonical API contract unless explicitly delegated.
• Record any API mismatches or unclear data dependencies for the Design Synchronizer.
• Preserve traceability to story IDs and FR/NFR IDs.