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
8. Local Fleet Canary

---

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/                # Infrastructure configuration (for example, OTEL collector)
├── 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. Use the local PGlite tier

The supported local tier is in-process PGlite and requires no PostgreSQL service. Leave DATABASE_URL unset for this route. Its default local configuration uses PGlite and performs no external database probe.

If a local queue service is useful, start only that non-PostgreSQL service:

docker compose up -d valkey

Do not use the current Compose PostgreSQL service: it mounts legacy infra/pg-init SQL and is not qualified for KBN-101. Start OTEL Collector or Jaeger individually only when needed and without starting PostgreSQL.

3. Gateway/Web local process (held)

Do not start the current Gateway or web process as a local PGlite route. Gateway first loads the daemon configuration and then project environment files without a tier guard; a pre-existing DATABASE_URL can select PostgreSQL, where current startup still reaches runtime DDL/migrations. Creating a root .env that omits DATABASE_URL does not make this safe, so neither a local credential file nor a web environment file is a current developer procedure.

PGlite remains the supported in-process data-layer implementation, and the optional Valkey command above remains safe because it does not start PostgreSQL. A safe Gateway/Web local procedure is held until KBN-101-02 rejects a daemon, inherited, root, or app-local PostgreSQL DSN and any non-local tier before connection or DDL; KBN-101-05 then supplies the production renderer/Vault process-exec or LoadCredential boundary.

Held future procedure

PostgreSQL local and federated deployment are held until KBN-101-00 (external bootstrap), KBN-101-03 (runner), and KBN-101-05 (renderer-backed deployment) land. The following is the held, non-operative future activation order with no current command authority:

external bootstrap → TLS/roles → mosaic-db-migrator --run → mosaic-db-migrator --verify → Gateway/Compose readiness.

Neither current Compose nor this development guide authorizes PostgreSQL initialization SQL, manual DDL, or a pre-runner start.

5. Gateway/Web start (held)

No Gateway/Web start command is currently authorized for the local PGlite route. Do not use root pnpm dev as a workaround: it additionally starts configured integrations and cannot establish the required local-tier/DSN isolation. Resume this section only after KBN-101-02 provides its fail-closed local-startup evidence.

---

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. Gateway MCP configuration (held)

Do not configure MCP endpoint credentials, write them to a local environment file, or restart the Gateway from this guide. Gateway/Web startup is held until KBN-101-02 supplies fail-closed local-tier/DSN isolation and KBN-101-05 supplies the renderer/Vault process-exec or LoadCredential secret-consumer interface. The future authenticated MCP route requires verified HTTPS and certificate validation; plaintext bearer-token examples are forbidden.

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.

PostgreSQL schema work (held)

Do not prepare or run a PostgreSQL target from this branch. The sole runner, bootstrap, and renderer are future KBN-101 artifacts, not current commands. When KBN-101-00/-03/-05 land, the owned activation documentation will require external bootstrap → TLS/roles → runner --run → runner --verify → Gateway/Compose readiness.

Generating migration artifacts

pnpm --filter @mosaicstack/db db:generate is an offline artifact-generation command. It does not authorize connecting to or initializing PostgreSQL. A future reviewed PostgreSQL procedure will determine when its output is applied.

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. Generate the offline artifact with pnpm --filter @mosaicstack/db db:generate.
4. Do not apply it to PostgreSQL until the future KBN-101 activation artifacts and their owned procedure are available. Direct schema push is not a production-like workflow.

---

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.