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Source-grounded rewrite of 529 published docs pages with per-unit information-loss verification: 1,713 factual corrections cited to src/**, generated surfaces regenerated, frontmatter titles preserved for i18n, release notes pages untouched. All docs gates green. Closes #100141
117 lines
4.3 KiB
Markdown
117 lines
4.3 KiB
Markdown
---
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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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The macOS app embeds an agent-controlled **Canvas panel** using `WKWebView`, a
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lightweight visual workspace for HTML/CSS/JS, A2UI, and small interactive UI
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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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- `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 switches as needed).
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Canvas can be disabled from Settings -> **Allow Canvas**. When disabled,
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canvas 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 show/hide the
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panel, navigate to a path or URL, evaluate JavaScript, and capture a
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snapshot image:
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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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`canvas.navigate` accepts local canvas paths, `http(s)` URLs, and `file://`
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URLs. Passing `"/"` 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
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panel. When the Gateway advertises a Canvas host, the macOS app auto-navigates
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to the A2UI host page on first open.
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Default A2UI host URL: `http://<gateway-host>:18789/__openclaw__/a2ui/`
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### A2UI commands (v0.8)
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Canvas accepts A2UI v0.8 server-to-client messages: `beginRendering`,
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`surfaceUpdate`, `dataModelUpdate`, `deleteSurface`. `createSurface` (v0.9) is
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not supported yet.
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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 test:
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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 `openclaw://agent?...` deep links:
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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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Supported query parameters:
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| Parameter | Meaning |
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| -------------------------- | ----------------------------------------------------- |
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| `message` | Prefilled agent prompt. |
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| `sessionKey` | Stable session identifier. |
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| `thinking` | Optional thinking profile. |
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| `deliver`, `to`, `channel` | Delivery target. |
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| `timeoutSeconds` | Optional run timeout. |
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| `key` | App-generated safety token for trusted local callers. |
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The app prompts for confirmation unless a valid key is provided. Unkeyed
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links show the message and URL before approval, and ignore delivery routing
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fields; keyed links use the normal Gateway run path.
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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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## Related
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- [macOS app](/platforms/macos)
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- [WebChat](/web/webchat)
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