NeuroSemantics AI

A minimalist mobile app for iOS and Android. The product is one thing only: an intelligent conversation partner with a specialized knowledge base in neurosemantics and NLP. No course portal, no CRM, no community.

Design language: calm, simple, clear. Off-white background, near-black text, one dark blue-green accent. No animations, no gradients.

System overview

apps/mobile      Expo / React Native app (two views: Chat, Paywall)
services/api     One Lambda backend (chat, usage, subscription verification)
infra            AWS CDK stack (the entire cloud environment)
db/migrations    SQL schema (two tables: users, usage)

A new developer should understand the whole system in under an hour. Every piece exists for a reason; if a feature does not make the core product better, it is not built.

Request flow

1. The user lands directly in the chat — no registration before the first question. Guests are identified by an app-generated device id (POST /guest/chat); dynamic conversation starters come from GET /suggestions (both public routes). The suggestions live in services/api/suggestions.json and can be updated with a deploy — no app release needed.
2. Requests go through API Gateway to the single Lambda; signed-in users use POST /chat with a Cognito JWT (Apple / Google / email via the hosted UI).
3. The Lambda calls the OpenAI Responses API with the Markdown knowledge base (services/api/knowledge/) as system instructions. The model returns structured output: a reply plus an analysis_ready flag.
4. Sign-in happens at the paywall, since a purchase must attach to an account. Usage counters live in PostgreSQL (Aurora Serverless v2).

The intelligent paywall

The paywall is not a hardcoded message count. Free conversations run in discovery mode: the model asks relevant follow-up questions, names patterns, shows understanding, and builds toward an analysis — without delivering the full solution. When the problem is described, the information is sufficient, and a concrete action plan is ready, the model signals analysis_ready, writes a calm transition ("…I have a concrete strategy I would recommend. Continue with Premium to see the analysis and the recommended steps."), and the conversation pauses.

The instructions explicitly forbid manufactured urgency, emotional pressure, fake readiness, and stopping mid-answer — Premium should feel like the natural continuation of an already valuable dialogue.

On unlock, the app resends the transcript; premium mode then delivers the full analysis, recommended strategies and concrete exercises immediately, and the dialogue continues without restriction.

A generous MESSAGE_CAP (default 200 per 30 days) exists purely as an abuse backstop for the free tier — it is not the paywall.

Conversations are never stored server-side; the client holds them in memory and sends the running transcript with each request. The database stores the absolute minimum: users (id, email, provider, subscription_status, created_at) and usage (messages_used, last_reset). No profiling, no training on user data. Error logging is anonymized (no message content).

Payments

Subscription logic is shared (services/api/src/subscription/); the payment provider differs per platform behind one PaymentProvider interface:

• iOS — In-App Purchase; the backend verifies the app receipt with Apple.
• Android — Google Play Billing; the backend verifies the purchase token with the Play Developer API.
• Web (future) — a Stripe adapter slots into the same interface.

Plans: Monthly and Yearly. Nothing else.

Getting started

npm install            # installs all workspaces
npm run lint
npm run typecheck
npm test

Mobile app

cd apps/mobile
npm start              # Expo dev server

Fill in extra in app.json (API URL, Cognito domain and client id) from the CDK stack outputs. In-app purchases require a development build (expo run:ios / expo run:android), not Expo Go.

Backend + infrastructure

cd infra
npx cdk deploy

After the first deploy:

1. Put values into the neurosemantics/app secret in Secrets Manager: OPENAI_API_KEY, APPLE_SHARED_SECRET, GOOGLE_SERVICE_ACCOUNT_JSON.
2. Run db/migrations/001_init.sql against the cluster (credentials are in the RDS-managed secret).
3. Optional: enable Apple/Google sign-in by passing CDK context (googleClientId, googleClientSecret, appleTeamId, appleKeyId, applePrivateKeySecretName). Email sign-in works out of the box.

CI/CD

GitHub Actions: ci.yml lints, type-checks and tests every PR; deploy.yml deploys the CDK stack on every push to main (set the AWS_DEPLOY_ROLE_ARN secret for OIDC). Store builds ship via EAS (eas build) when you choose to release.

Security

• All traffic over HTTPS. Account routes require a Cognito JWT; the two public routes (/suggestions, /guest/chat) carry no account data and are bounded by the free-tier message cap.
• Secrets live in AWS Secrets Manager only — no API keys in the client.
• The Lambda runs in private subnets; the database is not publicly reachable.

Product philosophy

Every free user should leave the app feeling that the system understood their situation, that a concrete analysis is ready, and that the next step is available in Premium — never that they were held back by an artificial interruption.

Every new feature must justify itself. The allowed AWS surface is API Gateway, Lambda, Cognito, S3, Secrets Manager and CloudWatch — and V1 does not even need S3. No Redis, no Kubernetes, no Kafka, no Elasticsearch, no queues, no microservices. One backend. Maximal simplicity.