bot/docs/platforms/mac/canvas.md

summary, read_when, title

summary	read_when	title
Agent-controlled Canvas panel embedded via WKWebView + custom URL scheme	Implementing the macOS Canvas panel Adding agent controls for visual workspace Debugging WKWebView canvas loads	Canvas

Canvas (macOS app)

The macOS app embeds an agent‑controlled Canvas panel using WKWebView. It is a lightweight visual workspace for HTML/CSS/JS, A2UI, and small interactive UI surfaces.

Where Canvas lives

Canvas state is stored under Application Support:

• ~/Library/Application Support/Bot/canvas/<session>/...

The Canvas panel serves those files via a custom URL scheme:

• bot-canvas://<session>/<path>

Examples:

• bot-canvas://main/ → <canvasRoot>/main/index.html
• bot-canvas://main/assets/app.css → <canvasRoot>/main/assets/app.css
• bot-canvas://main/widgets/todo/ → <canvasRoot>/main/widgets/todo/index.html

If no index.html exists at the root, the app shows a built‑in scaffold page.

Panel behavior

• Borderless, resizable panel anchored near the menu bar (or mouse cursor).
• Remembers size/position per session.
• Auto‑reloads when local canvas files change.
• Only one Canvas panel is visible at a time (session is switched as needed).

Canvas can be disabled from Settings → Allow Canvas. When disabled, canvas node commands return CANVAS_DISABLED.

Agent API surface

Canvas is exposed via the Gateway WebSocket, so the agent can:

• show/hide the panel
• navigate to a path or URL
• evaluate JavaScript
• capture a snapshot image

CLI examples:

bot nodes canvas present --node <id>
bot nodes canvas navigate --node <id> --url "/"
bot nodes canvas eval --node <id> --js "document.title"
bot nodes canvas snapshot --node <id>

Notes:

• canvas.navigate accepts local canvas paths, http(s) URLs, and file:// URLs.
• If you pass "/", the Canvas shows the local scaffold or index.html.

A2UI in Canvas

A2UI is hosted by the Gateway canvas host and rendered inside the Canvas panel. When the Gateway advertises a Canvas host, the macOS app auto‑navigates to the A2UI host page on first open.

Default A2UI host URL:

http://<gateway-host>:18789/__bot__/a2ui/

A2UI commands (v0.8)

Canvas currently accepts A2UI v0.8 server→client messages:

• beginRendering
• surfaceUpdate
• dataModelUpdate
• deleteSurface

createSurface (v0.9) is not supported.

CLI example:

cat > /tmp/a2ui-v0.8.jsonl <<'EOFA2'
{"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"}}}]}}
{"beginRendering":{"surfaceId":"main","root":"root"}}
EOFA2

bot nodes canvas a2ui push --jsonl /tmp/a2ui-v0.8.jsonl --node <id>

Quick smoke:

bot nodes canvas a2ui push --node <id> --text "Hello from A2UI"

Triggering agent runs from Canvas

Canvas can trigger new agent runs via deep links:

• bot://agent?...

Example (in JS):

window.location.href = "bot://agent?message=Review%20this%20design";

The app prompts for confirmation unless a valid key is provided.

Security notes

• Canvas scheme blocks directory traversal; files must live under the session root.
• Local Canvas content uses a custom scheme (no loopback server required).
• External http(s) URLs are allowed only when explicitly navigated.