/forge

Mobile Prototyping Reference

Purpose: Ship a demoable mobile prototype inside the ≤4h time-box. The prototype validates a single interaction or flow hypothesis — not the full app. Native capabilities are stubbed during STRIKE and swapped for real APIs only if the hypothesis survives.

Scope Boundary

• Forge mobile: throwaway-first mobile PoC (Expo / RN / Flutter), native capabilities stubbed, simulator-only by default.
• Native (elsewhere): production mobile build, store review prep, offline strategy, navigation architecture.

If the hypothesis asks "does this flow feel right?" → mobile. If it asks "does this scale under real network/battery/permissions?" → hand off to Native.

Stack Selection

Default: Expo — fastest time-to-demoable for single-slice PoC.

Workflow

SCAFFOLD  →  declare hypothesis + target platform (iOS / Android / both)
          →  pick framework, run CLI scaffold (`npx create-expo-app`)
          →  list native capabilities (camera / push / location / biometric / file)
          →  decide: stub all, stub critical path only, or real API

STRIKE    →  build single screen or flow (navigation min: 1-3 screens)
          →  stub native capabilities with Promise-returning mocks
          →  use deterministic mock data (avoid network in STRIKE)
          →  happy path demoable in simulator / Expo Go

COOL      →  verify on both orientations if relevant
          →  check safe-area insets (notch / home indicator)
          →  note skipped: keyboard avoidance, offline, deep-link, push perms
          →  screenshot / screen-record for PRESENT

PRESENT   →  ADOPT / ITERATE / DISCARD
          →  if ADOPT: hand off to Native with stubs + hypothesis outcome

Native Capability Stubs

Never wire real permissions during STRIKE. Ship mocks that return instantly.

// stubs/camera.ts
export async function takePhoto(): Promise<{ uri: string }> {
  await new Promise(r => setTimeout(r, 400)); // mimic shutter delay
  return { uri: 'https://picsum.photos/seed/photo/400/600' };
}

// stubs/location.ts
export async function getLocation(): Promise<{ lat: number; lng: number }> {
  return { lat: 35.6762, lng: 139.6503 }; // deterministic
}

// stubs/biometric.ts
export async function authenticate(): Promise<boolean> {
  await new Promise(r => setTimeout(r, 300));
  return true; // always succeed in PoC
}

Swap stubs → real APIs only at the ADOPT boundary, and hand off to Native.

Platform Preview Strategy

Default: Expo Go over QR code. If the hypothesis is "does the native API work?", real-device build is justified — but that's an mobile escape hatch, usually → Native.

Time-Box Anti-Patterns

• ❌ Bootstrap EAS build pipeline during PoC (adds 45+ min, adds zero hypothesis value).
• ❌ Wire real push notifications "just to show it works" — permission dialog breaks demo.
• ❌ Polish safe-area + keyboard avoidance + dark mode in one session.
• ❌ Add a navigation library when 2 screens and useState would suffice.
• ❌ Configure CodePush / OTA before knowing if the flow is kept.

What Goes in the Handoff to Native

• Screenshot or screen-recording of demoable flow.
• List of stubbed native capabilities (camera / location / push / biometric / file).
• Mock data shapes used (so Native can build real types).
• Known skipped: offline, deep-link, permission denial paths, locale, keyboard, push token lifecycle.
• Hypothesis outcome: what was learned, what flow changed, what the next production bet is.