/multi-platform

description: "Orchestrate cross-platform feature development across web, mobile, and desktop with API-first architecture"
argument-hint: "<feature description> [--platforms web,ios,android,desktop] [--shared-code evaluate|kotlin-multiplatform|typescript]"

Multi-Platform Feature Development Orchestrator

CRITICAL BEHAVIORAL RULES

You MUST follow these rules exactly. Violating any of them is a failure.

1. **Execute steps in order.** Do NOT skip ahead, reorder, or merge steps. 2. **Write output files.** Each step MUST produce its output file in `.multi-platform/` before the next step begins. Read from prior step files — do NOT rely on context window memory. 3. **Stop at checkpoints.** When you reach a `PHASE CHECKPOINT`, you MUST stop and wait for explicit user approval before continuing. Use the AskUserQuestion tool with clear options. 4. **Halt on failure.** If any step fails (agent error, test failure, missing dependency), STOP immediately. Present the error and ask the user how to proceed. Do NOT silently continue. 5. **Use only local agents.** All `subagent_type` references use agents bundled with this plugin or `general-purpose`. No cross-plugin dependencies. 6. **Never enter plan mode autonomously.** Do NOT use EnterPlanMode. This command IS the plan — execute it.

Pre-flight Checks

Before starting, perform these checks:

1. Check for existing session

Check if `.multi-platform/state.json` exists:

• If it exists and `status` is `"in_progress"`: Read it, display the current step, and ask the user:

  Found an in-progress multi-platform development session:
  Feature: [name from state]
  Current step: [step from state]

  1. Resume from where we left off
  2. Start fresh (archives existing session)

• If it exists and `status` is `"complete"`: Ask whether to archive and start fresh.

2. Initialize state

Create `.multi-platform/` directory and `state.json`:

{
  "feature": "$ARGUMENTS",
  "status": "in_progress",
  "platforms": ["web", "ios", "android"],
  "shared_code": "evaluate",
  "current_step": 1,
  "current_phase": 1,
  "completed_steps": [],
  "files_created": [],
  "started_at": "ISO_TIMESTAMP",
  "last_updated": "ISO_TIMESTAMP"
}

Parse `$ARGUMENTS` for `--platforms` and `--shared-code` flags. Use defaults if not specified.

3. Parse feature description

Extract the feature description from `$ARGUMENTS` (everything before the flags). This is referenced as `$FEATURE` in prompts below.

---

Phase 1: Architecture and API Design (Steps 1–3) — Sequential

Step 1: Define Feature Requirements and API Contracts

Use the Task tool to launch the backend architect:

Task:
  subagent_type: "multi-platform-apps-backend-architect"
  description: "Design API contract for $FEATURE"
  prompt: |
    Design the API contract for feature: $FEATURE.

    ## Target Platforms
    [List from state.json platforms]

    Create OpenAPI 3.1 specification with:
    - RESTful endpoints with proper HTTP methods and status codes
    - GraphQL schema if applicable for complex data queries
    - WebSocket events for real-time features
    - Request/response schemas with validation rules
    - Authentication and authorization requirements
    - Rate limiting and caching strategies
    - Error response formats and codes

    Define shared data models that all platforms will consume.

    ## Deliverables
    1. Complete API specification
    2. Shared data models
    3. Authentication flow design
    4. Integration guidelines for each platform

    Write your complete API design as a single markdown document.

Save the agent's output to `.multi-platform/01-api-contracts.md`.

Update `state.json`: set `current_step` to 2, add step 1 to `completed_steps`.

Step 2: Design System and UI/UX Consistency

Read `.multi-platform/01-api-contracts.md`.

Use the Task tool:

Task:
  subagent_type: "ui-ux-designer"
  description: "Create cross-platform design system for $FEATURE"
  prompt: |
    Create cross-platform design system for feature: $FEATURE.

    ## API Specification
    [Insert contents of .multi-platform/01-api-contracts.md]

    ## Target Platforms
    [List from state.json platforms]

    Include:
    - Component specifications for each platform (Material Design, iOS HIG, Fluent)
    - Responsive layouts for web (mobile-first approach)
    - Native patterns for iOS (SwiftUI) and Android (Material You)
    - Desktop-specific considerations (keyboard shortcuts, window management)
    - Accessibility requirements (WCAG 2.2 Level AA)
    - Dark/light theme specifications
    - Animation and transition guidelines

    ## Deliverables
    1. Design system documentation
    2. Component library specifications per platform
    3. Platform-specific guidelines
    4. Accessibility requirements
    5. Theme specifications

    Write your complete design system as a single markdown document.

Save the agent's output to `.multi-platform/02-design-system.md`.

Update `state.json`: set `current_step` to 3, add step 2 to `completed_steps`.

Step 3: Shared Business Logic Architecture

Read `.multi-platform/01-api-contracts.md` and `.multi-platform/02-design-system.md`.

Use the Task tool:

Task:
  subagent_type: "general-purpose"
  description: "Design shared business logic architecture for $FEATURE"
  prompt: |
    You are a software architect specializing in cross-platform shared code architecture.
    Design shared business logic architecture for cross-platform feature: $FEATURE.

    ## API Contracts
    [Insert contents of .multi-platform/01-api-contracts.md]

    ## Design System
    [Insert contents of .multi-platform/02-design-system.md]

    Define:
    - Core domain models and entities (platform-agnostic)
    - Business rules and validation logic
    - State management patterns (MVI/Redux/BLoC)
    - Caching and offline strategies
    - Error handling and retry policies
    - Platform-specific adapter patterns

    Consider Ko