Flow: HCI Research Platform

A production-shaped prototype for HCI research combining a multi-bot conversation engine built on LangChain primitives, React PWA frontend, passkey-first authentication (via h4ckath0n), SSE-based real-time chat, and vendor-neutral Web Push notifications.

Architecture Overview

Pillar	Stack	Description
Backend	FastAPI + h4ckath0n + SQLAlchemy 2.x	Async API with passkey auth, multi-tenant project model, and SSE fan-out
Conversation Engine	LangChain agents + Router	Multi-bot architecture: Router (single writer) + Intake/Feedback/Coach specialists with proposal/commit flow
Frontend	React 19 + Vite + Tailwind CSS	PWA with service worker, SSE streaming chat, and Web Push notification support

Conversation Engine Architecture

The engine uses a Router + specialist architecture:

• Router — Routes each turn to the correct specialist, validates all patch proposals, and owns the only commit path to UserProfile (Store A) and Memory (Store B).
• Intake Bot — Onboarding and profile setup. Can propose updates to onboarding fields.
• Feedback Bot — Habit tracking and barrier analysis. Can propose rolling coaching field updates and memory items.
• Coach Bot — Normal conversation and encouragement. Can propose candidates only (higher confidence threshold).

All bots use LangChain agents and tools. Proposals are validated against a permission matrix with confidence thresholds and evidence span requirements. See docs/current-architecture.md for full details.

Quick Start

Backend

cd api
uv sync
# Copy .env.example to .env and configure
cp ../.env.example ../.env
uv run uvicorn app.main:app --reload

Frontend (in another terminal)

cd web
npm install
npm run dev

The frontend dev server runs at http://localhost:5173 and proxies API requests to the backend.

Project Structure

Flow/
├── api/                          # FastAPI backend
│   ├── app/
│   │   ├── main.py               # App entry point (h4ckath0n create_app)
│   │   ├── routes.py             # API route handlers
│   │   ├── models.py             # SQLAlchemy 2.x models (incl. UserProfile, Memory, AuditLog)
│   │   ├── db.py                 # Database session management
│   │   ├── middleware.py         # CSP and other middleware
│   │   ├── id_utils.py           # Custom ID generation (p... / u...)
│   │   ├── agents/               # NEW: Multi-bot LangChain agents
│   │   │   ├── engine.py         # Turn engine: Router + specialist pipeline
│   │   │   ├── router.py         # Routing coordinator (structured output)
│   │   │   ├── intake.py         # Intake specialist agent
│   │   │   ├── feedback.py       # Feedback specialist agent
│   │   │   ├── coach.py          # Coach specialist agent
│   │   │   └── orchestrator.py   # Legacy orchestrator (backward compat)
│   │   ├── schemas/              # Pydantic models
│   │   │   ├── router.py         # RouteDecision (INTAKE/FEEDBACK/COACH)
│   │   │   ├── patches.py        # Proposals, evidence, permissions, profile/memory schemas
│   │   │   └── tool_schemas.py   # Legacy tool argument schemas
│   │   ├── services/             # NEW: Business logic layer
│   │   │   └── profile_service.py # Profile/memory persistence, validation, audit
│   │   ├── tools/                # LangChain tools
│   │   │   ├── proposal_tools.py # NEW: propose_profile_patch, propose_memory_patch
│   │   │   └── langchain_tools.py # Legacy tool wrappers
│   │   └── engine/               # Legacy conversation engine (deprecated for new work)
│   │       ├── flow.py           # Legacy orchestrator
│   │       ├── modules.py        # IntakeModule, FeedbackModule, tool loop
│   │       ├── state.py          # State enums, Pydantic models, DataKeys
│   │       ├── tools.py          # Tool implementations
│   │       ├── scheduler.py      # Daily prompts, reminders, auto-feedback
│   │       └── tone.py           # Tone adaptation (EMA, hysteresis, whitelist)
│   ├── prompts/                  # System prompt templates
│   ├── tests/                    # Backend test suite
│   └── pyproject.toml
├── web/                          # React PWA frontend
│   ├── public/
│   │   ├── manifest.json         # PWA web app manifest
│   │   └── sw.js                 # Service worker (push + notificationclick)
│   ├── src/
│   │   ├── App.tsx               # Route definitions
│   │   ├── pages/                # Page components
│   │   │   ├── Dashboard.tsx     # Project thread list
│   │   │   ├── Activation.tsx    # Join project via invite link
│   │   │   ├── ChatThread.tsx    # Real-time chat with SSE
│   │   │   ├── Notifications.tsx # Push notification management
│   │   │   ├── Landing.tsx       # Public landing page
│   │   │   ├── Login.tsx         # Passkey login
│   │   │   ├── Register.tsx      # Passkey registration
│   │   │   └── Settings.tsx      # User settings
│   │   ├── auth/                 # Passkey auth (from h4ckath0n scaffold)
│   │   ├── api/                  # API client and types
│   │   ├── components/           # Shared UI components
│   │   └── gen/                  # Generated OpenAPI TypeScript client
│   └── package.json
├── docs/
│   ├── current-architecture.md           # NEW: Current architecture (authoritative)
│   ├── legacy-conversation-flow-contract.md   # DEPRECATED: Legacy behavior reference
│   └── parity-matrix.md                       # Legacy → new code mapping
├── .env.example
└── AGENTS.md                     # Agent behavior rules

API Endpoints

All project-scoped endpoints require passkey authentication.

Method	Path	Tag	Description
GET	/healthz	infra	Readiness probe
GET	/dashboard	dashboard	List user's project memberships
POST	/p/{project_id}/activate/claim	activation	Claim invite code, create membership + conversation
GET	/p/{project_id}/me	activation	Get membership status, conversation ID, stored email
POST	/p/{project_id}/messages	messaging	Send message, get assistant reply
GET	/p/{project_id}/events	streaming	SSE event stream for real-time updates
GET	/p/{project_id}/push/vapid-public-key	push	Get VAPID public key for push subscription
POST	/p/{project_id}/push/subscribe	push	Store a push subscription
POST	/p/{project_id}/push/unsubscribe	push	Revoke a push subscription
GET	/demo/ping	demo	Liveness ping
POST	/demo/echo	demo	Echo with reverse
GET	/demo/sse	demo	Authenticated SSE demo stream
WS	/demo/ws	demo	Authenticated WebSocket demo

Data Model

Table	ID Type	Description
projects	p... (custom, 32 chars)	User-visible research projects
project_invites	auto-increment int	Hashed invite codes with expiry
project_memberships	auto-increment int	Links (project, user) with status; unique constraint
participant_contacts	auto-increment int	Optional email contact metadata (not used for identity)
conversations	auto-increment int	1:1 with membership
messages	auto-increment int	Chat history with server_msg_id (UUID)
conversation_runtime_state	FK to conversation	JSON blob for engine state
user_profiles	auto-increment int	Store A — structured profile JSON (1:1 with membership)
memory_items	auto-increment int	Store B — semi-structured memory items per membership
patch_audit_log	auto-increment int	Audit trail: proposals, decisions, commits
push_subscriptions	auto-increment int	Web Push endpoints + crypto keys per device
outbox_events	auto-increment int	Durable scheduled events with dedupe keys

Conversation Engine

The engine implements the architecture defined in docs/current-architecture.md.

Turn Pipeline

1. Persist user message
2. Load UserProfile (Store A) + Memory (Store B) + recent chat history
3. Router decides which specialist to run (INTAKE, FEEDBACK, or COACH)
4. Invoke specialist agent (LangChain tool-calling agent)
5. Collect patch proposals made during the agent run
6. Router validates proposals (permissions, confidence, evidence) and commits approved ones
7. Persist assistant message
8. Emit SSE events for UI update

Routing

Condition	Route
Required onboarding fields missing	INTAKE
Currently in feedback protocol	FEEDBACK
Profile complete, normal conversation	COACH

Proposal + Commit Flow

Specialist bots propose changes via propose_profile_patch and propose_memory_patch tools. The Router validates each proposal against:

• Permission matrix: Intake → onboarding fields, Feedback → coaching fields, Coach → candidates only
• Confidence thresholds: INTAKE/FEEDBACK ≥ 0.5, COACH ≥ 0.8
• Evidence spans: Must reference recent message IDs
• Memory rules: Items ≤ 500 chars with source pointers

All proposals and decisions are logged in the patch_audit_log table.

Legacy Engine

The legacy conversation flow engine (api/app/engine/) is retained for backward compatibility. The legacy behavioral contract (docs/legacy-conversation-flow-contract.md) is deprecated.

Frontend Pages

Route	Page	Description
/	Landing	Public landing page
/register	Register	Passkey registration
/login	Login	Passkey login
/dashboard	Dashboard	List project threads (active/ended)
/p/:projectId/activate	Activation	Join project via invite link, collect optional email
/p/:projectId/chat	ChatThread	Send messages via POST, receive via SSE
/p/:projectId/notifications	Notifications	PWA install guidance, enable push notifications
/settings	Settings	User settings

PWA & Push Notifications

• Web App Manifest — web/public/manifest.json enables "Add to Home Screen"
• Service Worker (web/public/sw.js):
  • Handles push events → shows system notifications
  • Handles notificationclick → deep-links to the relevant project chat (/p/{project_id}/chat)
• Subscription flow: explicit user action → request permission → subscribe with VAPID public key from backend → store subscription server-side
• iOS: "Add to Home Screen" guidance is shown before enabling notifications

Tests

Backend

cd api && uv run python -m pytest tests/ -v

Test modules:

• test_api.py — API endpoint integration tests (messaging wired to new engine)
• test_new_architecture.py — NEW: Router permissions, confidence thresholds, evidence spans, profile/memory validation, proposal tools, deterministic routing
• test_engine_integration.py — NEW: Full turn pipeline with async DB, profile persistence, memory persistence, audit log
• test_langchain_router.py — Router structured output and deterministic routing
• test_langchain_agents.py — Agent tool permissions and orchestrator pipeline
• test_langchain_tools.py — LangChain tool schemas and invocation
• test_flow.py — Legacy conversation engine routing and history
• test_scheduler.py — Daily prompts, reminders, auto-feedback, intensity
• test_tone.py — Tone adaptation, EMA, whitelist validation
• test_tools.py — Tool execution and state management

Verify Patch Audit Behavior

The audit trail can be inspected by querying the patch_audit_log table after processing messages. The test_engine_integration.py::TestAuditLog tests verify that proposals and commit decisions are properly recorded.

Frontend

cd web && npm test         # Unit tests (Vitest)
cd web && npm run test:e2e # E2E tests (Playwright)

What Is Stubbed

This is a prototype. The following are mocked or incomplete:

• LLM calls — In stub mode, specialist agents return fixed responses. Connect a real LLM (OpenAI, Anthropic, etc.) by passing llm and router_llm parameters to the engine.
• Web Push delivery — Push subscriptions are stored in the database but no actual push messages are sent. Wire up pywebpush with VAPID keys to enable delivery.
• Outbox event processing — Outbox events (reminders, auto-feedback timers) are created with dedupe keys but no background worker processes them. Add a polling worker or task queue to fire events at available_at.
• Message endpoint — POST /p/{project_id}/messages runs the Router + specialist pipeline in stub mode (deterministic routing, fixed responses). With a real LLM, it produces contextual responses.

Environment Variables

Configure in .env at the repository root (see .env.example):

Variable	Description
H4CKATH0N_ENV	Environment mode (development / production)
H4CKATH0N_DATABASE_URL	SQLAlchemy async database URL
H4CKATH0N_AUTH_SIGNING_KEY	Hex secret for JWT signing
H4CKATH0N_RP_ID	WebAuthn relying party ID (e.g., localhost)
H4CKATH0N_ORIGIN	Allowed origin for CORS and WebAuthn
VITE_API_BASE_URL	API base URL for the frontend (e.g., /api)
VAPID_PUBLIC_KEY	VAPID public key for Web Push
VAPID_PRIVATE_KEY	VAPID private key for Web Push (never log this)

License

See LICENSE.