This is a full-stack AI chat platform (DIAL Chat) built as a monorepo with a NestJS backend-for-frontend (BFF) and a React single-page application. The backend proxies all requests to an external DIAL Core service, handling authentication (OIDC providers, cookie sessions, header tokens, CSRF), configuration aggregation (env, static defaults, feature flags), file management (upload, archive download, sharing, batch operations), conversation lifecycle (CRUD, streaming with SSE, naming, publishing/unpublishing, sharing by invitation), and skills/prompts/toolsets management with manifest import/export. The frontend provides a rich chat UI with conversation panel, attachment input with canvas for previewing PDFs, Office docs, images, and MCP app iframes, a catalog browser for models/agents/toolsets, scheduled tasks with recurrence forms, skill and prompt editors, usage limits dashboards, and overlay embedding for third-party host apps. Both apps share extensive typed libraries (22 private packages) covering the catalog, conversation hooks, shared UI components, and a generated OpenAPI client. The system follows a strict BFF pattern: the frontend never communicates directly with DIAL Core—all API calls go through the NestJS server, which adds session validation, resource ownership checks, and caching. Streaming chat completions use server-sent events (SSE) with a consistent init payload format. The overlay embedding protocol uses postMessage with a documented state machine, feature flags gated by backend configuration. Observable telemetry via OpenTelemetry instruments HTTP lifecycle, generation metrics, and runtime diagnostics with Prometheus endpoints. The codebase is thoroughly tested (Vitest for frontend, Supertest for NestJS integration, browser-level CSP tests) and includes CI/CD pipelines for OpenAPI regeneration, deployment, and e2e testing. Architecture is modular: domain-specific NestJS services are split into focused sub-services (e.g., ConversationsService delegates to ConversationListingService, ConversationPersistenceService, ConversationLifecycleService, ConversationStreamingService). React contexts are used for state management (no Redux), with custom hooks for entity operations. The monorepo leverages Nx for task orchestration, dependency graph enforcement, and bundle budget checks in libraries. External dependencies include DIAL Core (for AI model inference and file storage), various OIDC providers, and optional libraries like MCP UI client for sandboxed app rendering.