Cactus + PowerSync Expo Demo

Disclaimer: much of this code was generated using LLMs, however some basic QA was performed by a human.

Tech demo app for:

• React Native (Expo)
• Supabase Auth + Storage
• Cactus on-device inference (LLM + STT)
• PowerSync React Native SDK
• PowerSync Attachments

Implemented demo sections

• Home: sync status and cumulative cost-savings estimates.
• Transcription: on-device STT with run metrics stored in PowerSync.
• RAG: local document corpus, on-device embeddings/retrieval, local answer generation.
• Attachments: PowerSync attachment queue + Supabase Storage bucket files.
• Offline: forced offline mode, queued local writes, pending CRUD count.

Prerequisites

• Node.js 18+
• pnpm
• Xcode (for iOS) or Android Studio (for Android)
• An iOS simulator or Android emulator (no paid Apple Developer account required for simulator builds)

Setup

1. Install dependencies

pnpm install

2. Configure environment (optional for local testing)

The RAG and Transcription screens work fully offline without any credentials — the Cactus model runs on-device. Sync, Attachments, and Home stats require a PowerSync + Supabase backend.

Create .env.local in the project root to enable cloud sync:

POWERSYNC_URL=https://your-instance.powersync.journeyapps.com
SUPABASE_URL=https://your-project.supabase.co
SUPABASE_ANON_KEY=your-anon-key
CACTUS_API_KEY=your-cactus-key   # optional

If .env.local is absent the app still builds and runs — sync features will be inactive.

3. Apply Supabase schema (only needed for cloud sync)

Run supabase/schema.sql against your Supabase project, and create a Storage bucket named files.

4. Build and run

This app uses native modules (cactus-react-native, op-sqlite, PowerSync) so it cannot run in Expo Go. You must do a native build the first time.

iOS simulator (no Apple Developer account needed):

pnpm ios
# equivalent to: expo run:ios

Android emulator:

pnpm android
# equivalent to: expo run:android

This generates the ios/ or android/ native project, builds it, installs it on your simulator/emulator, and starts Metro — all in one command.

Subsequent runs

After the first build the app is installed. You can start just the Metro bundler:

pnpm start

Then press i to open iOS or a to open Android. If you add or change native dependencies, re-run pnpm ios / pnpm android to rebuild.

Notes

• Cost values are estimated model numbers for demo visualization only.
• Attachment metadata is tracked in demo_files; file blobs are stored in Supabase Storage bucket files.
• The on-device LLM model is downloaded at runtime from within the app (see the RAG and Transcription screens).