open-design/docs/architecture.md

Architecture

Parent: spec.md · Siblings: skills-protocol.md · agent-adapters.md · modes.md

This doc describes the system topology, runtime modes, data flow, and file layout. Design rationale lives in spec.md; protocol details for skills and agent adapters live in their own docs.

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1. Three deployment topologies

OD is a web app plus a local daemon. The split means the same UI can run in three shapes:

Topology A — Fully local (the default)

┌────────────────── user's machine ──────────────────┐
│                                                    │
│   browser ──► Next.js dev server (localhost:3000)  │
│                       │                            │
│                       │ http://localhost:7456      │
│                       ▼                            │
│            od daemon (Node, long-running)         │
│                       │                            │
│                       ▼                            │
│            spawns: claude / codex / cursor / …     │
└────────────────────────────────────────────────────┘

One pnpm tools-dev run web starts both the Next.js app and the daemon. pnpm tools-dev adds the desktop shell. Zero config. No accounts.

Topology B — Web on Vercel + daemon on user's machine

browser ──► od.yourdomain.com (Vercel)
              │
              │ ws(s):// user-provided URL (e.g. cloudflared tunnel)
              ▼
        od daemon on user's laptop
              │
              ▼
        spawns: claude / codex / …

The user runs od daemon --expose which prints a tunnel URL; they paste the URL into the deployed web app's "Connect daemon" screen. Daemon holds secrets; Vercel holds nothing sensitive.

Topology C — Web on Vercel + direct API (no daemon)

browser ──► od.yourdomain.com (Vercel serverless)
                       │
                       ▼
              Anthropic Messages API (BYOK stored in browser)

No local CLI, no daemon. Degraded experience — no Claude Code skills, no filesystem artifacts (stored in IndexedDB), no PPTX export. But it's the "just try it" path. Keys stored localStorage with explicit warning.

The three topologies share the same web bundle; the difference is which transports are enabled.

2. Component diagram (logical)

┌─────────────────────────────── Web App ─────────────────────────────┐
│                                                                     │
│  ┌──────────┐  ┌─────────────┐  ┌───────────┐  ┌────────────────┐  │
│  │ chat pane│  │ artifact    │  │ preview   │  │ comment /      │  │
│  │          │  │ tree        │  │ iframe    │  │ slider overlay │  │
│  └────┬─────┘  └──────┬──────┘  └─────┬─────┘  └────────┬───────┘  │
│       │               │               │                  │           │
│       └─────────── session bus (in-memory) ──────────────┘           │
│                        │                                             │
│                        ▼                                             │
│              Transport layer (daemon SSE | api-direct | browser)      │
└─────────────────────────┬───────────────────────────────────────────┘
                          │
  ┌───────────────────────┴────────────────────────────────┐
  │                                                        │
  ▼ (topology A/B)                                         ▼ (topology C)
┌─────────────────────── Daemon ───────────────────────┐  ┌────────────┐
│                                                      │  │ browser-   │
│  session manager      skill registry                 │  │ only       │
│  agent adapter pool   design-system resolver         │  │ runtime    │
│  artifact store       preview compile pipeline       │  │ (limited)  │
│  export pipeline      detection service              │  └────────────┘
│                                                      │
└─┬────────────────────────────────────────────────┬───┘
  │                                                │
  ▼                                                ▼
┌─ agent CLIs ─┐                           ┌─ filesystem ─┐
│ claude       │                           │ ./.od/      │
│ codex        │                           │ ~/.od/      │
│ cursor-agent │                           │ skills/      │
│ gemini       │                           │ DESIGN.md    │
│ opencode     │                           └──────────────┘
│ qwen         │
└──────────────┘

3. Key components

3.1 Web app (Next.js 16, App Router)

• Why Next.js, not Vite SPA? We want SSR for the marketing landing page + serverless routes for Topology C's direct-API path + Vercel deployment as a first-class citizen. An SPA would need a separate server for any of that.
• State: React/browser state for UI config, with projects/conversations/files hydrated from the daemon APIs.
• Iframe preview: Vendored React 18 + Babel standalone for JSX artifacts, following Open CoDesign's approach. HTML artifacts load raw. See §5.
• Comment mode: Click captures [data-od-id] on preview DOM, opens a popover, sends {artifact_id, element_id, note} to daemon → agent gets a surgical edit instruction.
• Slider UI: When an agent emits a "tweak parameter" tool call (see skills-protocol.md §4.2), the web app renders a live-update control that re-sends parameterized prompts without round-tripping the chat.

3.2 Local daemon (od daemon)

Single binary via pkg or a thin Node script distributed over npm. Responsibilities:

• Listen on http://localhost:7456 by default. Accept REST/SSE routes under /api/*.
• Maintain a session per web tab. Sessions hold: active agent, active skill, active artifact, in-flight tool calls, design-system reference.
• Operate the agent adapter pool: one detected CLI = one adapter instance, reused across sessions.
• Scan and index skills from ~/.claude/skills/, ./skills/, ./.claude/skills/ on startup and on FS-watch events.
• Own the artifact store — writes files to disk, never in memory.
• Run the preview compile pipeline (Babel transform for JSX, CSS inliner for HTML exports).
• Provide export hooks for HTML/PDF/ZIP and skill-defined deck outputs.

3.3 Agent adapter pool

See agent-adapters.md for the full interface. Each adapter:

1. Detects its target CLI (PATH lookup + config-dir probe).
2. Spawns the CLI with a standardized wrapper prompt + skill context + design-system context + CWD set to the project's artifact root.
3. Streams stdout/stderr as structured events (JSON Lines if the CLI supports it; line-based parser otherwise).
4. Reports capabilities — does it support multi-turn? Surgical edits? Native skill loading? Tool use?

3.4 Skill registry

See skills-protocol.md. Scans three locations and merges:

Source	Priority	Purpose
./.claude/skills/	highest	project-private skills
./skills/	medium	project-declared skills
~/.claude/skills/	lowest	user-global skills

Conflicts resolve by priority (higher wins). Each skill parsed once; watched for changes in dev.

3.5 Design-system resolver

• Looks for ./DESIGN.md first, then ./design-system/DESIGN.md, then user-configured path.
• Parses the 9-section format (see awesome-claude-design schema).
• Injects as a prepended system message on every agent run, plus as a {{ design_system }} template variable skills can reference.
• Hot-reloads on file change in dev.

3.6 Artifact store

Plain files on disk. Conventional layout per project:

./.od/
├── config.json                  # project-level daemon config
├── artifacts/
│   ├── 2026-04-24T10-03-12-landing/
│   │   ├── artifact.json        # metadata (skill, mode, prompt, parent)
│   │   ├── index.html           # primary output (or .jsx, .md, .pptx.json)
│   │   └── assets/              # skill-generated images, fonts, etc.
│   └── …
├── history.jsonl                # append-only action log (generations, edits, comments)
└── sessions/
    └── <session-id>.json        # transient; garbage-collected after 24h

Rationale:

• Plain files → users can git add ./.od/artifacts/ and review designs in PRs.
• artifact.json metadata → OD can reconstruct the artifact tree without a DB.
• history.jsonl not SQLite → append-only, git-friendly, greppable. Open CoDesign uses SQLite; we deliberately don't.
• Sessions separate from artifacts → sessions are ephemeral UI state; artifacts are durable.

3.7 Export pipeline

Format	How
HTML (self-contained)	Inline all CSS, rewrite asset URLs to data: URIs
PDF	puppeteer → page.pdf() on the rendered HTML
PPTX	deck-skill outputs a JSON intermediate (slides.json); pptxgenjs generates the .pptx
ZIP	archiver over artifacts/<id>/
Markdown	direct copy if artifact is .md, otherwise skill-defined render

4. Data flow — a typical "generate prototype" turn

1. User types prompt in web chat.
2. Web sends { method: "session.generate", params: {
        sessionId, prompt, modeHint: "prototype"
   }} to daemon via WS.

3. Daemon:
     a. picks active skill (prototype-skill)
     b. loads design-system (DESIGN.md)
     c. materializes a new artifact dir under ./.od/artifacts/<slug>/
     d. invokes agent adapter with:
          - system: skill's SKILL.md contents + DESIGN.md
          - user: original prompt
          - cwd: the new artifact dir
     e. streams agent events back to web as they arrive:
          - "tool_call" (edit file, write file, read file)
          - "text_delta"
          - "thinking" (if supported)

4. Web shows:
     - running tool-call feed in the side panel
     - artifact tree updates as files materialize
     - preview iframe loads the primary output file when agent signals "done"
     - slider/comment overlay activates once preview loads

5. On completion, daemon appends:
     { ts, sessionId, artifactId, action: "generate", skill, promptHash }
   to history.jsonl.

6. User comments on an element → web sends { method: "session.refine", params: {
        sessionId, artifactId, elementId, note }}

7. Daemon re-invokes agent with surgical-edit instruction + the note.
   Adapter translates based on capabilities:
     - Claude Code → native tool loop, edits that region only
     - Codex → regenerates the file with "only change element X" constraint
     - API fallback → same as Codex path

5. Preview renderer

Constraints:

• Must isolate artifact code from the host app (no access to window, cookies, parent DOM).
• Must hot-reload as the agent streams writes.
• Must support both static HTML and JSX artifacts.

Design:

• Always an <iframe sandbox="allow-scripts"> — no allow-same-origin.
• Static HTML: srcdoc load of the inlined artifact.
• JSX: inject a small bootstrap that imports vendored React 18 + Babel standalone, then dynamically evals the JSX as Babel-transformed code. (This is what Open CoDesign does, and it works; no reason to reinvent.)
• Agent writes trigger a debounced rebuild + iframe srcdoc replace. Full reload each time — React state loss is acceptable at this scope.

6. Config files

File	Purpose
~/.open-design/config.toml	daemon-global: default agent preference, keys (optional, BYOK), telemetry opt-in (default off)
~/.open-design/agents.json	cached agent detection results
./.od/config.json	project-local: active design system, preferred skills, preferred mode
./skills/<skill>/SKILL.md	skill manifest (standard Claude Code format)
./DESIGN.md	active design system (awesome-claude-design format)

All config is plain text / TOML / JSON — no binary formats, no sqlite. Reviewable in PRs.

7. Protocol between web and daemon

The shipped daemon uses HTTP routes plus Server-Sent Events for streaming chat output. This keeps the browser on the same /api/* surface in dev and production while still allowing incremental agent output.

Representative API surface:

GET  /api/health
GET  /api/agents
GET  /api/skills
GET  /api/design-systems
GET  /api/projects
POST /api/projects
GET  /api/projects/:id/files
POST /api/projects/:id/upload
POST /api/chat              -> text/event-stream
POST /api/artifacts/save

Full schema in schemas/protocol.md (TODO: write).

8. Deployment

Local

pnpm install
pnpm tools-dev run web       # starts daemon + web foreground loop

When a reverse proxy sits in front of the daemon, /api/* includes SSE streams and must stay unbuffered. The daemon sends Cache-Control: no-cache, no-transform and X-Accel-Buffering: no, and also emits SSE comment keepalives, but nginx can still break chunked streams if gzip is enabled. For nginx, set proxy_buffering off;, gzip off;, and long proxy_read_timeout / proxy_send_timeout values on the API location. Otherwise browsers can report net::ERR_INCOMPLETE_CHUNKED_ENCODING 200 (OK) on long generations.

Docker

# docker-compose.yml
services:
  daemon:
    image: openclaudedesign/daemon
    volumes: [ "~/.open-design:/root/.open-design", "./:/workspace" ]
    ports: ["7456:7456"]
  web:
    image: openclaudedesign/web
    ports: ["3000:3000"]
    environment: [ "OD_DAEMON_URL=http://daemon:7456" ]

Vercel + local daemon (Topology B)

vercel deploy                     # web only
od daemon --expose               # user runs locally; prints tunnel URL
# user pastes URL into /connect UI

Vercel direct (Topology C)

vercel deploy                     # same bundle
# flip VERCEL env flag OD_MODE=direct to hide daemon-connect UI

9. Security model

Surface	Threat	Mitigation
Daemon HTTP/SSE API	Arbitrary local process talks to daemon	Bind to localhost by default; add auth/tunnel hardening before exposing beyond the machine
Artifact code in preview	XSS/cookie theft from host	<iframe sandbox="allow-scripts">, no allow-same-origin
Agent running on user's machine	Agent reads/writes outside project	Adapter sets cwd to artifact dir; relies on agent's own permission system (Claude Code's --allowed-tools etc.)
User secrets	Leak to cloud	BYOK stored only in daemon's config.toml (mode 0600) or browser localStorage in Topology C, never sent to OD's own servers (we don't have any)
Skill from untrusted source	Malicious skill in ~/.claude/skills/	Install-time warning; skills run under the agent's permission model, not ours
Vercel web bundle	Compromised build	Standard Vercel integrity; bundle has zero secrets

We inherit the agent's permission model on purpose — we don't invent our own sandbox, because Claude Code's --permission-mode / Codex's sandboxing / Cursor's containment already exist and are maintained.

10. Performance notes

• Daemon startup: < 500 ms (lazy adapter init).
• Agent detection: < 200 ms (parallel PATH probes).
• First generation latency: dominated by agent model time; OD overhead should be < 50 ms.
• Preview reload: debounced 100 ms on artifact file writes.
• Skill index: cold scan < 100 ms for ~50 skills; watched with chokidar.

11. What's explicitly out of scope for MVP

• Multi-user / RBAC / orgs
• Hosted skill marketplace (git URLs only in v1)
• Figma export (post-1.0, same as Open CoDesign)
• Collaborative editing
• Mobile web support (desktop only in MVP)
• Offline mode (beyond "the agent is local" — we don't cache model responses)