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trails/openspec/changes/mobile-nearby-sync/proposal.md
Ullrich Schäfer fff77a2ed2
Add mobile app, map-core, nearby sync, and activity recording specs 
mobile-app: Unified React Native + Expo app combining Planner and
Journal. OAuth2 PKCE auth, MapLibre maps, versioned REST API with
Zod schemas, configurable server URL, offline SQLite, Web Push relay
notifications. TanStack Query + Zustand state management. Jest +
Maestro testing. 76 tasks across 5 phases.

map-core-package: Extract renderer-agnostic map definitions (tiles,
color palettes, POI categories, z-index) into @trails-cool/map-core.
Pure refactor preparing for MapLibre on mobile. 27 tasks.

mobile-activity-recording: GPS recording, live stats, HealthKit/Health
Connect export. Separated from mobile-app for independent scheduling.

mobile-nearby-sync: BLE route sync between nearby devices for offline
group riding. QR waypoint sharing as simpler v1. TXQR noted as future.

journal-rest-api spec: Full API contract — endpoints, auth, pagination,
errors, discovery, versioning, BRouter proxy.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
2026-04-12 21:52:30 +02:00

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Why

When bikepacking or hiking in a group, one person may update the route at the last café with WiFi. Once the group is in the middle of nowhere with no signal, the others are stuck with the old route. There's no way to share route updates between nearby devices without internet.

What Changes

  • BLE route sync: Devices discover each other via Bluetooth LE and transfer route data (waypoints + GPX geometry) directly. Uses react-native-ble-plx for cross-platform iOS ↔ Android compatibility.
  • QR waypoint sharing (v1, simpler): Generate a QR code with compressed waypoint coordinates. The receiver scans it and gets the waypoints immediately — full route geometry recomputes when signal returns.
  • Sync protocol: A lightweight protocol over BLE that handles discovery ("who nearby has this route?"), versioning ("is your copy newer than mine?"), and transfer (chunked GPX data).

Capabilities

New Capabilities

  • mobile-nearby-sync: BLE-based route sync between nearby devices, QR waypoint sharing fallback

Non-Goals

  • Real-time collaborative editing over BLE (too complex — this is one-shot sync)
  • Syncing activities or other data (routes only for v1)
  • Mesh networking (direct device-to-device only, no relay through third devices)

Impact

  • Depends on mobile-app change being implemented first
  • New dependency: react-native-ble-plx (requires Expo dev build)
  • BLE background advertising needs careful battery management
  • iOS requires Bluetooth usage description in Info.plist
  • Android requires BLUETOOTH_SCAN, BLUETOOTH_CONNECT, BLUETOOTH_ADVERTISE permissions

Future ideas

  • TXQR (animated QR codes via camera) as an alternative transfer method — ~13KB/s demonstrated, no pairing needed, but requires porting the fountain code protocol to TypeScript