# Architecture

**Parent:** [`spec.md`](spec.md) · **Siblings:** [`skills-protocol.md`](skills-protocol.md) · [`agent-adapters.md`](agent-adapters.md) · [`modes.md`](modes.md)

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

[ocod]: https://github.com/OpenCoworkAI/open-codesign
[acd]: https://github.com/VoltAgent/awesome-claude-design
[piai]: https://github.com/mariozechner/pi-ai
[guizang]: https://github.com/op7418/guizang-ppt-skill

---

## 1. Three deployment topologies

OCD 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)  │
│                       │                            │
│                       │ ws://localhost:7431        │
│                       ▼                            │
│            ocd daemon (Node, long-running)         │
│                       │                            │
│                       ▼                            │
│            spawns: claude / codex / cursor / …     │
└────────────────────────────────────────────────────┘
```

One `pnpm dev` starts both the Next.js app and the daemon (via a predev script). Zero config. No accounts.

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

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

The user runs `ocd 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 ──► ocd.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 (ws-rpc | http-direct | indexeddb)      │
└─────────────────────────┬───────────────────────────────────────────┘
                          │
  ┌───────────────────────┴────────────────────────────────┐
  │                                                        │
  ▼ (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       │                           │ ./.ocd/      │
│ codex        │                           │ ~/.ocd/      │
│ cursor-agent │                           │ skills/      │
│ gemini       │                           │ DESIGN.md    │
│ opencode     │                           └──────────────┘
│ openclaw     │
└──────────────┘
```

## 3. Key components

### 3.1 Web app (Next.js 15, 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:** Zustand for session/artifact stores. Browser-side only; hydrated from daemon on connect.
- **Iframe preview:** Vendored React 18 + Babel standalone for JSX artifacts, following [Open CoDesign][ocod]'s approach. HTML artifacts load raw. See [§5](#5-preview-renderer).
- **Comment mode:** Click captures `[data-ocd-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`](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 (`ocd daemon`)

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

- Listen on `ws://localhost:7431` (configurable). Accept JSON-RPC-over-WebSocket.
- 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).
- Spawn headless Chromium via Puppeteer for **PDF export**. PPTX via `pptxgenjs`.

### 3.3 Agent adapter pool

See [`agent-adapters.md`](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`](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][acd] 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:

```
./.ocd/
├── 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 ./.ocd/artifacts/` and review designs in PRs.
- **`artifact.json` metadata** → OCD can reconstruct the artifact tree without a DB.
- **`history.jsonl` not SQLite** → append-only, git-friendly, greppable. [Open CoDesign][ocod] 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 ./.ocd/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][ocod] 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-claude-design/config.toml` | daemon-global: default agent preference, keys (optional, BYOK), telemetry opt-in (default off) |
| `~/.open-claude-design/agents.json` | cached agent detection results |
| `./.ocd/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][acd] format) |

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

## 7. Protocol between web and daemon

JSON-RPC 2.0 over WebSocket. Why not REST? Because we need streaming. Why not gRPC? Over-engineering for a single-origin local app.

Methods (MVP):

```
session.open(params) -> { sessionId }
session.generate(params) -> streams: tool_call | text_delta | artifact_update | done
session.refine(params) -> streams: same
session.cancel(params) -> { ok }
agents.list() -> [{ id, name, version, capabilities }]
agents.setActive({ agentId }) -> { ok }
skills.list() -> [{ id, name, mode, manifest }]
skills.setActive({ sessionId, skillId }) -> { ok }
skills.install({ source }) -> streams: progress
design.setActive({ path }) -> { designSystem }
artifacts.list({ projectRoot }) -> [Artifact]
artifacts.get({ id }) -> Artifact
artifacts.export({ id, format }) -> streams: progress | { url | path }
```

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

## 8. Deployment

### Local
```sh
pnpm install
pnpm dev           # starts daemon on :7431, next on :3000
```

### Docker
```yaml
# docker-compose.yml
services:
  daemon:
    image: openclaudedesign/daemon
    volumes: [ "~/.open-claude-design:/root/.open-claude-design", "./:/workspace" ]
    ports: ["7431:7431"]
  web:
    image: openclaudedesign/web
    ports: ["3000:3000"]
    environment: [ "OCD_DAEMON_URL=ws://daemon:7431" ]
```

### Vercel + local daemon (Topology B)
```sh
vercel deploy                     # web only
ocd daemon --expose               # user runs locally; prints tunnel URL
# user pastes URL into /connect UI
```

### Vercel direct (Topology C)
```sh
vercel deploy                     # same bundle
# flip VERCEL env flag OCD_MODE=direct to hide daemon-connect UI
```

## 9. Security model

| Surface | Threat | Mitigation |
|---|---|---|
| Daemon WebSocket | Arbitrary local process talks to daemon | Token handshake; token printed on `ocd daemon` start, required in WS URL |
| 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 OCD'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; OCD 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][ocod])
- Collaborative editing
- Mobile web support (desktop only in MVP)
- Offline mode (beyond "the agent is local" — we don't cache model responses)
