stack/docs/guides/dev-guide.md

Mosaic Stack — Developer Guide

Table of Contents

1. Architecture Overview
2. Local Development Setup
3. Building and Testing
4. Adding New Agent Tools
5. Adding New MCP Tools
6. Database Schema and Migrations
7. API Endpoint Reference

---

Architecture Overview

Mosaic Stack is a TypeScript monorepo managed with pnpm workspaces and Turborepo.

mosaic-mono-v1/
├── apps/
│   ├── gateway/          # NestJS + Fastify API server
│   └── web/              # Next.js 16 + React 19 web dashboard
├── packages/
│   ├── agent/            # Agent session types (shared)
│   ├── auth/             # BetterAuth configuration
│   ├── brain/            # Structured data layer (projects, tasks, missions)
│   ├── cli/              # mosaic CLI and TUI (Ink)
│   ├── coord/            # Mission coordination engine
│   ├── db/               # Drizzle ORM schema, migrations, client
│   ├── design-tokens/    # Shared design system tokens
│   ├── log/              # Agent log ingestion and tiering
│   ├── memory/           # Preference and insight storage
│   ├── mosaic/           # Install wizard and bootstrap utilities
│   ├── prdy/             # PRD wizard CLI
│   ├── quality-rails/    # Code quality scaffolder CLI
│   ├── queue/            # Valkey-backed task queue
│   └── types/            # Shared TypeScript types
├── docker/               # Dockerfile(s) for containerized deployment
├── infra/                # Infra config (OTEL collector, pg-init scripts)
├── docker-compose.yml    # Local services (Postgres, Valkey, OTEL, Jaeger)
└── CLAUDE.md             # Project conventions for AI coding agents

Key Technology Choices

Concern	Technology
API framework	NestJS with Fastify adapter
Web framework	Next.js 16 (App Router), React 19
ORM	Drizzle ORM
Database	PostgreSQL 17 + pgvector extension
Auth	BetterAuth
Agent harness	Pi SDK (@mariozechner/pi-coding-agent)
Queue	Valkey 8 (Redis-compatible)
Build	pnpm workspaces + Turborepo
CI	Woodpecker CI
Observability	OpenTelemetry → Jaeger
Module resolution	NodeNext (ESM everywhere)

Module System

All packages use "type": "module" and NodeNext resolution. Import paths must include the .js extension even when the source file is .ts.

NestJS @Inject() decorators must be used explicitly because tsx/esbuild does not support emitDecoratorMetadata.

---

Local Development Setup

Prerequisites

• Node.js 20+
• pnpm 9+
• Docker and Docker Compose

1. Clone and Install Dependencies

git clone <repo-url> mosaic-mono-v1
cd mosaic-mono-v1
pnpm install

2. Start Infrastructure Services

docker compose up -d

This starts:

Service	Port	Description
PostgreSQL 17 + pgvector	5433 (host)	Primary database
Valkey 8	6380 (host)	Queue and cache
OpenTelemetry Collector	4317, 4318	OTEL gRPC and HTTP
Jaeger	16686	Distributed trace UI

3. Configure Environment

Create a .env file in the monorepo root:

# Database (matches docker-compose defaults)
DATABASE_URL=postgresql://mosaic:mosaic@localhost:5433/mosaic

# Auth (required — generate a random 32+ char string)
BETTER_AUTH_SECRET=change-me-to-a-random-secret

# Gateway
GATEWAY_PORT=14242
GATEWAY_CORS_ORIGIN=http://localhost:3000

# Web
NEXT_PUBLIC_GATEWAY_URL=http://localhost:14242

# Optional: Ollama
OLLAMA_BASE_URL=http://localhost:11434
OLLAMA_MODELS=llama3.2

The gateway loads .env from the monorepo root via dotenv at startup (apps/gateway/src/main.ts).

4. Push the Database Schema

pnpm --filter @mosaicstack/db db:push

This applies the Drizzle schema directly to the database (development only; use migrations in production).

5. Start the Gateway

pnpm --filter @mosaicstack/gateway exec tsx src/main.ts

The gateway starts on port 14242 by default.

6. Start the Web App

pnpm --filter @mosaicstack/web dev

The web app starts on port 3000 by default.

---

Building and Testing

TypeScript Typecheck

pnpm typecheck

Runs tsc --noEmit across all packages in dependency order via Turborepo.

Lint

pnpm lint

Runs ESLint across all packages. Config is in eslint.config.mjs at the root.

Format Check

pnpm format:check

Runs Prettier in check mode. To auto-fix:

pnpm format

Tests

pnpm test

Runs Vitest across all packages. The workspace config is at vitest.workspace.ts.

Build

pnpm build

Builds all packages and apps in dependency order.

Pre-Push Gates (MANDATORY)

All three must pass before any push:

pnpm format:check && pnpm typecheck && pnpm lint

A pre-push hook enforces this mechanically.

---

Adding New Agent Tools

Agent tools are Pi SDK ToolDefinition objects registered in apps/gateway/src/agent/agent.service.ts.

1. Create a Tool Factory File

Add a new file in apps/gateway/src/agent/tools/:

// apps/gateway/src/agent/tools/my-tools.ts
import { Type } from '@sinclair/typebox';
import type { ToolDefinition } from '@mariozechner/pi-coding-agent';

export function createMyTools(): ToolDefinition[] {
  const myTool: ToolDefinition = {
    name: 'my_tool_name',
    label: 'Human Readable Label',
    description: 'What this tool does.',
    parameters: Type.Object({
      input: Type.String({ description: 'The input parameter' }),
    }),
    async execute(_toolCallId, params) {
      const { input } = params as { input: string };
      const result = `Processed: ${input}`;
      return {
        content: [{ type: 'text' as const, text: result }],
        details: undefined,
      };
    },
  };

  return [myTool];
}

2. Register the Tools in AgentService

In apps/gateway/src/agent/agent.service.ts, import and call your factory alongside the existing tool registrations:

import { createMyTools } from './tools/my-tools.js';

// Inside the session creation logic where tools are assembled:
const tools: ToolDefinition[] = [
  ...createBrainTools(this.brain),
  ...createCoordTools(this.coordService),
  ...createMemoryTools(this.memory, this.embeddingService),
  ...createFileTools(sandboxDir),
  ...createGitTools(sandboxDir),
  ...createShellTools(sandboxDir),
  ...createWebTools(),
  ...createMyTools(), // Add this line
  ...mcpTools,
  ...skillTools,
];

3. Export from the Tools Index

Add an export to apps/gateway/src/agent/tools/index.ts:

export { createMyTools } from './my-tools.js';

4. Typecheck and Test

pnpm typecheck
pnpm test

---

Adding New MCP Tools

Mosaic connects to external MCP servers via McpClientService. To expose tools from a new MCP server:

1. Run an MCP Server

Implement a standard MCP server that exposes tools via the streamable HTTP transport or SSE transport. The server must accept connections at a /mcp endpoint.

2. Configure MCP_SERVERS

In your .env:

MCP_SERVERS='[{"name":"my-server","url":"http://localhost:3001/mcp"}]'

With authentication:

MCP_SERVERS='[{"name":"secure-server","url":"http://my-server/mcp","headers":{"Authorization":"Bearer token"}}]'

3. Restart the Gateway

On startup, McpClientService (apps/gateway/src/mcp-client/mcp-client.service.ts) connects to each configured server, calls tools/list, and bridges the results to Pi SDK ToolDefinition format. These tools become available in all new agent sessions.

Tool Naming

Bridged MCP tool names are taken directly from the MCP server's tool manifest. Ensure names do not conflict with built-in tools (check apps/gateway/src/agent/tools/).

---

Database Schema and Migrations

The schema lives in a single file: packages/db/src/schema.ts

Schema Overview

Table	Purpose
users	User accounts (BetterAuth-compatible)
sessions	Auth sessions
accounts	OAuth accounts
verifications	Email verification tokens
projects	Project records
missions	Mission records (linked to projects)
tasks	Task records (linked to projects and/or missions)
conversations	Chat conversation metadata
messages	Individual chat messages
preferences	Per-user key-value preference store
insights	Vector-embedded memory insights
agent_logs	Agent interaction logs (hot/warm/cold tiers)
skills	Installed agent skills
summarization_jobs	Log summarization job tracking

The insights table uses a vector(1536) column (pgvector) for semantic search.

Development: Push Schema

Apply schema changes directly to the dev database (no migration files created):

pnpm --filter @mosaicstack/db db:push

Generating Migrations

For production-safe, versioned changes:

pnpm --filter @mosaicstack/db db:generate

This creates a new SQL migration file in packages/db/drizzle/.

Running Migrations

pnpm --filter @mosaicstack/db db:migrate

Drizzle Config

Config is at packages/db/drizzle.config.ts. The schema file path and output directory are defined there.

Adding a New Table

1. Add the table definition to packages/db/src/schema.ts.
2. Export it from packages/db/src/index.ts.
3. Run pnpm --filter @mosaicstack/db db:push (dev) or pnpm --filter @mosaicstack/db db:generate && pnpm --filter @mosaicstack/db db:migrate (production).

---

API Endpoint Reference

All endpoints are served by the gateway at http://localhost:14242 by default.

Authentication

Authentication uses BetterAuth session cookies. The auth handler is mounted at /api/auth/* via a Fastify low-level hook in apps/gateway/src/auth/auth.controller.ts.

Endpoint	Method	Description
/api/auth/sign-in/email	POST	Sign in with email/password
/api/auth/sign-up/email	POST	Register a new account
/api/auth/sign-out	POST	Sign out (clears session cookie)
/api/auth/get-session	GET	Returns the current session

Chat

WebSocket namespace /chat (Socket.IO). Authentication via session cookie.

Events sent by the client:

Event	Payload	Description
message	{ content, conversationId?, provider?, modelId? }	Send a message

Events emitted by the server:

Event	Payload	Description
token	{ token, conversationId }	Streaming token
end	{ conversationId }	Stream complete
error	{ message }	Error during streaming

HTTP endpoints (apps/gateway/src/chat/chat.controller.ts):

Endpoint	Method	Auth	Description
/api/chat/conversations	GET	User	List conversations
/api/chat/conversations/:id/messages	GET	User	Get messages for a conversation

Admin

All admin endpoints require role = admin.

Endpoint	Method	Description
GET /api/admin/users	GET	List all users
GET /api/admin/users/:id	GET	Get a single user
POST /api/admin/users	POST	Create a user
PATCH /api/admin/users/:id/role	PATCH	Update user role
POST /api/admin/users/:id/ban	POST	Ban a user
POST /api/admin/users/:id/unban	POST	Unban a user
DELETE /api/admin/users/:id	DELETE	Delete a user
GET /api/admin/health	GET	System health status

Agent / Providers

Endpoint	Method	Auth	Description
GET /api/agent/providers	GET	User	List all providers and their models
GET /api/agent/providers/models	GET	User	List available models
POST /api/agent/providers/:id/test	POST	User	Test provider connectivity

Projects / Brain

Endpoint	Method	Auth	Description
GET /api/brain/projects	GET	User	List projects
POST /api/brain/projects	POST	User	Create a project
GET /api/brain/projects/:id	GET	User	Get a project
PATCH /api/brain/projects/:id	PATCH	User	Update a project
DELETE /api/brain/projects/:id	DELETE	User	Delete a project
GET /api/brain/tasks	GET	User	List tasks
POST /api/brain/tasks	POST	User	Create a task
GET /api/brain/tasks/:id	GET	User	Get a task
PATCH /api/brain/tasks/:id	PATCH	User	Update a task
DELETE /api/brain/tasks/:id	DELETE	User	Delete a task

Memory / Preferences

Endpoint	Method	Auth	Description
GET /api/memory/preferences	GET	User	Get user preferences
PUT /api/memory/preferences	PUT	User	Upsert a preference

MCP Server (Gateway-side)

Endpoint	Method	Auth	Description
POST /mcp	POST	User (session cookie or Authorization header)	MCP streamable HTTP transport
GET /mcp	GET	User	MCP SSE stream reconnect

Skills

Endpoint	Method	Auth	Description
GET /api/skills	GET	User	List installed skills
POST /api/skills	POST	Admin	Install a skill
PATCH /api/skills/:id	PATCH	Admin	Update a skill
DELETE /api/skills/:id	DELETE	Admin	Remove a skill

Coord (Mission Coordination)

Endpoint	Method	Auth	Description
GET /api/coord/missions	GET	User	List missions
POST /api/coord/missions	POST	User	Create a mission
GET /api/coord/missions/:id	GET	User	Get a mission
PATCH /api/coord/missions/:id	PATCH	User	Update a mission

Observability

OpenTelemetry traces are exported to the OTEL collector (OTEL_EXPORTER_OTLP_ENDPOINT). View traces in Jaeger at http://localhost:16686.

Tracing is initialized before NestJS bootstrap in apps/gateway/src/tracing.ts. The import order in apps/gateway/src/main.ts is intentional: import './tracing.js' must come before any NestJS imports.