126 lines
3.6 KiB
Markdown
126 lines
3.6 KiB
Markdown
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---
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summary: "Agent-controlled Canvas panel embedded via WKWebView + custom URL scheme"
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read_when:
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- Implementing the macOS Canvas panel
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- Adding agent controls for visual workspace
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- Debugging WKWebView canvas loads
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title: "Canvas"
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---
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# Canvas (macOS app)
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The macOS app embeds an agent‑controlled **Canvas panel** using `WKWebView`. It
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is a lightweight visual workspace for HTML/CSS/JS, A2UI, and small interactive
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UI surfaces.
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## Where Canvas lives
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Canvas state is stored under Application Support:
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- `~/Library/Application Support/OpenClaw/canvas/<session>/...`
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The Canvas panel serves those files via a **custom URL scheme**:
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- `openclaw-canvas://<session>/<path>`
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Examples:
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- `openclaw-canvas://main/` → `<canvasRoot>/main/index.html`
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- `openclaw-canvas://main/assets/app.css` → `<canvasRoot>/main/assets/app.css`
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- `openclaw-canvas://main/widgets/todo/` → `<canvasRoot>/main/widgets/todo/index.html`
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If no `index.html` exists at the root, the app shows a **built‑in scaffold page**.
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## Panel behavior
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- Borderless, resizable panel anchored near the menu bar (or mouse cursor).
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- Remembers size/position per session.
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- Auto‑reloads when local canvas files change.
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- Only one Canvas panel is visible at a time (session is switched as needed).
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Canvas can be disabled from Settings → **Allow Canvas**. When disabled, canvas
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node commands return `CANVAS_DISABLED`.
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## Agent API surface
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Canvas is exposed via the **Gateway WebSocket**, so the agent can:
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- show/hide the panel
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- navigate to a path or URL
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- evaluate JavaScript
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- capture a snapshot image
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CLI examples:
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```bash
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openclaw nodes canvas present --node <id>
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openclaw nodes canvas navigate --node <id> --url "/"
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openclaw nodes canvas eval --node <id> --js "document.title"
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openclaw nodes canvas snapshot --node <id>
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```
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Notes:
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- `canvas.navigate` accepts **local canvas paths**, `http(s)` URLs, and `file://` URLs.
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- If you pass `"/"`, the Canvas shows the local scaffold or `index.html`.
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## A2UI in Canvas
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A2UI is hosted by the Gateway canvas host and rendered inside the Canvas panel.
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When the Gateway advertises a Canvas host, the macOS app auto‑navigates to the
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A2UI host page on first open.
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Default A2UI host URL:
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```
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http://<gateway-host>:18789/__openclaw__/a2ui/
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```
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### A2UI commands (v0.8)
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Canvas currently accepts **A2UI v0.8** server→client messages:
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- `beginRendering`
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- `surfaceUpdate`
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- `dataModelUpdate`
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- `deleteSurface`
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`createSurface` (v0.9) is not supported.
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CLI example:
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```bash
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cat > /tmp/a2ui-v0.8.jsonl <<'EOFA2'
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{"surfaceUpdate":{"surfaceId":"main","components":[{"id":"root","component":{"Column":{"children":{"explicitList":["title","content"]}}}},{"id":"title","component":{"Text":{"text":{"literalString":"Canvas (A2UI v0.8)"},"usageHint":"h1"}}},{"id":"content","component":{"Text":{"text":{"literalString":"If you can read this, A2UI push works."},"usageHint":"body"}}}]}}
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{"beginRendering":{"surfaceId":"main","root":"root"}}
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EOFA2
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openclaw nodes canvas a2ui push --jsonl /tmp/a2ui-v0.8.jsonl --node <id>
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```
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Quick smoke:
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```bash
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openclaw nodes canvas a2ui push --node <id> --text "Hello from A2UI"
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```
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## Triggering agent runs from Canvas
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Canvas can trigger new agent runs via deep links:
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- `openclaw://agent?...`
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Example (in JS):
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```js
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window.location.href = "openclaw://agent?message=Review%20this%20design";
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```
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The app prompts for confirmation unless a valid key is provided.
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## Security notes
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- Canvas scheme blocks directory traversal; files must live under the session root.
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- Local Canvas content uses a custom scheme (no loopback server required).
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- External `http(s)` URLs are allowed only when explicitly navigated.
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