React Native (Expo) + Firebase Engineer for K-2 Math App(8–10wk)

Sarafis Abacus — a teacher-ready number-sense app for Grades 1–2. Children learn make-10, compose/decompose, and place-value with a dual-color abacus (5/10) and guided 5–7′ lessons. MVP is English-only (architecture i18n-ready).

Engagement: Fixed-price with milestones + PAID test task. Start ASAP.

What you’ll build (MVP)
1. Abacus Engine (“rekenrek+”)
• 8–10 rails, dual-color 5/10, smooth gestures/animations (60 fps).
• Automatic exchanges: 10 ones→1 ten, 10 tens→1 hundred, etc., with visual/audio cues.
• Place-value indicators (Ones/Tens/Hundreds/Thousands).
2. Three modes
• Guided micro-lessons (5–7′).
• Practice/Challenges (timed rounds, streaks, badges).
• Sandbox for teachers incl. projector “curtain” to hide/reveal.
3. Four initial lesson units
• Counting & Number Sense; Compose/Decompose; Make-10 (over the ten); Add/Subtract 2-digit (with/without regrouping).
4. Teacher basics
• Quick progress overview (per skill), export simple PDF handouts.
5. App qualities
• Offline-first (usable with no signal; sync when online).
• Accessibility: large targets; left/right-hand toggle; color-blind-safe patterns; haptics & audio cues.
• No ads. Child-friendly flows.

Tech stack (must-have)
• React Native (Expo managed, TypeScript)
• Animations/Gestures: react-native-reanimated, react-native-gesture-handler
• Rendering: @shopify/react-native-skia (or equivalent)
• State: lightweight (Zustand or Redux Toolkit)
• Firebase (EU region): Auth (email + Apple/Google), Firestore (offline persistence), Storage, Cloud Messaging (FCM), Analytics (GA4), Crashlytics, App Check
• Build/Release: EAS Build/Submit (TestFlight / Google Play Internal)
• Audio/TTS: expo-av / expo-speech (English)
• Quality: Jest + RN Testing Library; basic Detox E2E for one core flow

Non-functional requirements
• Targets: iOS 16+, Android 10+; phones first, tablets OK.
• Performance: 60 fps interactions on mid-range devices; cold launch <3s.
• Security: Firestore Security Rules (role-based), least-privilege IAM, App Check.
• Privacy: data minimization, EU data residency, GDPR-aware; COPPA-friendly (no ads/tracking for kids).
• Content: lessons/strings bundled locally (JSON) + remote config flags.

Deliverables & milestones (fixed price)
M1 — Abacus Engine (Week 1–2): rails, gestures, one exchange (10 ones→1 ten). Acceptance: 60 fps demo + Expo build.
M2 — Lesson System & Make-10 (Week 3): lesson runner; full Make-10 unit; offline persistence. Acceptance: run offline; GA4 events; TestFlight/Play build.
M3 — Compose/Decompose + 2-digit Add/Sub (Week 4–5): units + 10-round challenge; local progress syncs to Firestore. Acceptance: works offline→online.
M4 — Teacher Basics & Sandbox Curtain (Week 6): curtain mode; reports lite (attempts, accuracy, time); PDF export. Acceptance: sample class report PDF; GA4 key events.
M5 — QA & Beta (Week 7–8): accessibility pass; Crashlytics; FCM streak reminder; store-ready builds + README, setup docs, test plan.

Acceptance criteria (sample)
• Functional: exchanges correct across O/T/H/Th; guided steps never dead-end.
• Offline: all lessons run in airplane mode; sync on reconnect.
• Analytics: GA4 events — session_start, lesson_start/complete, make10_success, exchange_event, error_count.
• Performance: avg frame time ≤16.7ms; memory stable.
• Security: Firestore Rules reviewed; App Check enabled; no secrets in repo.
• Release: EAS pipelines; signed artifacts; crash-free sessions ≥99% in beta.

How we’ll work
• Tools: GitHub (private), Expo EAS, Notion/Trello, Slack.
• Cadence: weekly demo (20–30 min); async daily update (3 bullets).
• Code: PRs with reviews; small feature branches.

Paid test task (8–12 hours)
Mini abacus with 8 rails, dual-color 5/10, one exchange (10 ones→1 ten) + simple Make-10 stepper. Save a local progress flag and sync to Firestore when online. Deliver Expo link + short Loom + repo. This task is paid.

Your profile (must-have)
• 2+ shipped React Native (Expo) apps (links) and Firebase mobile experience (Firestore offline, Rules, FCM, GA4).
• Strong animations/gestures; performance mindset.
• Clear English communication; reliable & proactive.

Proposal instructions (include)
1. Two app links + your role.
2. Offline-first pattern you use with Firestore.
3. How you’d implement exchange logic at 60 fps.
4. Fixed-price per milestone + total for 8–10 weeks; earliest start.
5. Confirmation you accept: IP assignment, NDA, GDPR-friendly handling, milestone-based payments.