Tech stack

Languages & runtime

TypeScript-first. Project-owned entrypoints, modules, scripts, tests, reporters and configs default to TS. Residual .js / .mjs / .cjs files need an explicit generated/vendor/compatibility reason and pass pnpm check:residual-js (scripts/check-residual-js.ts).
Node.js ~24 (per AGENTS.md — "Runtime target is Node ~24").
pnpm 10.33.2 via Corepack, monorepo (pnpm-workspace.yaml) covering apps/*, packages/*, tools/*, e2e.
Some daemon source files use // @ts-nocheck (e.g. apps/daemon/src/server.ts:1, agents.ts:1) — the team gets type checking via the contracts package while keeping the dynamic Express-style code looser. Strict packages: contracts, sidecar-proto, sidecar, platform.

Frontend

Next.js 16 App Router + React 18 (apps/web/).
- Single dynamic catch-all: apps/web/app/[[...slug]]/page.tsx. Returns <ClientApp /> + generateStaticParams(). The whole app is a SPA; routing handled at runtime by apps/web/src/router.ts reading window.location.
- No app/api/* — every API call goes to the daemon via proxy.
Tailwind-style utility CSS in index.css (no Tailwind toolchain visible; styling is hand-rolled with CSS variables matching the OKLch design-system tokens).
i18n: lightweight apps/web/src/i18n/ (manual dictionaries for English / Simplified Chinese / Japanese / Korean / Deutsch / Traditional Chinese, mirroring the README translations).
State in apps/web/src/state/:
- config.ts — app config persisted to localStorage (api keys, model selection, theme, agent ids).
- projects.ts — REST helpers that hit /api/projects.
- maxTokens.ts + litellm-models.json — vendored model context/output caps from BerriAI/litellm.
Iframe-based preview:
- apps/web/src/runtime/srcdoc.ts:17-36 — wraps HTML artifacts for <iframe sandbox="allow-scripts"> previews; injects a localStorage shim so cross-origin sandbox doesn't SecurityError.
- apps/web/src/runtime/react-component.ts:9-80 — loads React 18 + Babel Standalone via CDN inside the iframe and transpiles user JSX at preview time.
Markdown rendered by a hand-rolled mini-parser in apps/web/src/runtime/markdown.tsx (no external lib).
ZIP export is a pure client-side stored-mode encoder with CRC32 in apps/web/src/runtime/zip.ts:43-80 — no JSZip dep.

Backend (daemon)

Express + multer (apps/daemon/src/server.ts:2-3) — one Node process listens on localhost:7456 (overridable). HTTP + Server-Sent Events.
better-sqlite3 (per imports in apps/daemon/src/db.ts) — single SQLite file at ~/.open-design/app.sqlite (or OD_DATA_DIR-relative).
node:child_process spawn for every code-agent CLI; stdio piping with type-aware stream parsers.
puppeteer for PDF export (referenced in docs/architecture.md:181-183 as the planned PDF path).

Desktop / packaged

Electron (apps/desktop/, apps/packaged/).
esbuild for sidecar bundling (apps/daemon/sidecar/, apps/web/sidecar/, packages/sidecar/esbuild.config.mjs, etc.).
pkg-style packaging is aspirational in docs; the active path is the Electron sidecar runtime.

Agent transport protocols

The daemon supports five distinct stream formats, one per family of CLIs:

Format	Used by	Parser
`claude-stream-json`	Claude Code	`apps/daemon/src/claude-stream.ts`
`copilot-stream-json`	GitHub Copilot CLI	`apps/daemon/src/copilot-stream.ts`
`acp-json-rpc` (Agent Client Protocol)	Devin, Hermes, Kimi, Kiro	`apps/daemon/src/acp.ts`
`pi-rpc`	Pi (`mariozechner/pi-ai`)	`apps/daemon/src/pi-rpc.ts`
`json-event-stream`	Codex, Gemini, OpenCode, Cursor Agent	`apps/daemon/src/json-event-stream.ts`
`plain` (fallback)	Qwen and any other	`apps/daemon/src/json-event-stream.ts`

Each maps the CLI's native event shape onto a unified { type: 'text_delta' | 'thinking_delta' | 'tool_use' | 'tool_result' | 'status' | 'usage' | 'done', … } event the browser consumes via SSE.

Media providers

apps/daemon/src/media-models.ts and media.ts describe a provider router dispatching to:

Provider	Surfaces	Notes
OpenAI	image (gpt-image-2/1, dall-e-3), audio (gpt-4o-mini-tts)	Auto-detects Azure OpenAI by base URL. Sync.
Volcengine (ByteDance)	image (Seedream), video (Seedance 2.0 t2v / i2v with audio)	Async task polling.
xAI Grok	image, video, audio (`grok-imagine-*`)	Hybrid sync + async.
HyperFrames	video (HTML→MP4)	Local renderer, no API key.
Stubs (intentional)	placeholder generators	Gated by `OD_MEDIA_ALLOW_STUBS=1`; otherwise 503.

Deployment

Vercel (apps/daemon/src/deploy.ts:1-616) — direct upload of an HTML file set + asset rewrites + optional analytics hook injection. Token in ~/.open-design/vercel.json.
Local-only is the default topology.

Why these picks (where the source/docs hint at it)

Next.js over a Vite SPA because of SSR for marketing + Vercel-deploy-as-first-class (docs/architecture.md:107).
SQLite over a hosted DB — single-user, single-machine MVP, plain-file-friendly. The team deliberately rejected SQLite for artifacts (kept those as plain files) but kept SQLite for projects/conversations/messages metadata.
Express over Fastify/Hono — pragmatic, well-known, fine for localhost:7456 traffic.
Hand-rolled markdown / ZIP / direction library — keeps frontend bundle small and avoids supply-chain footprint where the surface is small.
Vendored React 18 + Babel for iframe — borrowed from Open CoDesign because it works and reinventing it isn't the bet.
Five-format stream parsers instead of one canonical protocol — the bet is "agents have already converged on a few strong implementations; talk to all of them rather than reinvent" (docs/agent-adapters.md:7-9). The cost is five parsers; the payoff is broad agent coverage.