159 lines
7.6 KiB
Markdown
159 lines
7.6 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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---
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# Canvas (macOS app)
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Status: draft spec · Date: 2025-12-12
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Clawdis can embed an agent-controlled “visual workspace” panel (“Canvas”) inside the macOS app using `WKWebView`, served via a **custom URL scheme** (no loopback HTTP port required).
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This is designed for:
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- Agent-written HTML/CSS/JS on disk (per-session directory).
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- A real browser engine for layout, rendering, and basic interactivity.
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- Agent-driven visibility (show/hide), navigation, DOM/JS queries, and snapshots.
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- Minimal chrome: borderless panel; bezel/chrome appears only on hover.
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## Why a custom scheme (vs. loopback HTTP)
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Using `WKURLSchemeHandler` keeps Canvas entirely in-process:
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- No port conflicts and no extra local server lifecycle.
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- Easier to sandbox: only serve files we explicitly map.
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- Works offline and can use an ephemeral data store (no persistent cookies/cache).
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If a Canvas page truly needs “real web” semantics (CORS, fetch to loopback endpoints, service workers), consider the loopback-server variant instead (out of scope for this doc).
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## URL ↔ directory mapping
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The Canvas scheme is:
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- `clawdis-canvas://<session>/<path>`
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Routing model:
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- `clawdis-canvas://main/` → `<canvasRoot>/main/index.html` (or `index.htm`)
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- `clawdis-canvas://main/yolo` → `<canvasRoot>/main/yolo/index.html` (or `index.htm`)
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- `clawdis-canvas://main/assets/app.css` → `<canvasRoot>/main/assets/app.css`
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Directory listings are not served.
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When `/` has no `index.html` yet, the handler serves a **built-in A2UI shell** (bundled with the macOS app).
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This gives the agent a ready-to-render UI surface without requiring any on-disk HTML.
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If the A2UI shell resources are missing (dev misconfiguration), Canvas falls back to a simple built-in welcome page.
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### Reserved built-in paths
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The scheme handler serves bundled assets under:
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- `clawdis-canvas://<session>/__clawdis__/a2ui/...`
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This is reserved for app-owned assets (not session content) and is backed by `Bundle.module` resources.
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### Suggested on-disk location
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Store Canvas state under the app support directory:
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- `~/Library/Application Support/Clawdis/canvas/<session>/…`
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This keeps it alongside other app-owned state and avoids mixing with `~/.clawdis/` gateway config.
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## Panel behavior (agent-controlled)
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Canvas is presented as a borderless `NSPanel` (similar to the existing WebChat panel):
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- Can be shown/hidden at any time by the agent.
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- Supports an “anchored” presentation (near the menu bar icon or another anchor rect).
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- Uses a rounded container; shadow stays on, but **chrome/bezel only appears on hover**.
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- Default position is the **top-right corner** of the current screen’s visible frame (unless the user moved/resized it previously).
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- The panel is **user-resizable** (edge resize + hover resize handle) and the last frame is persisted per session.
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### Hover-only chrome
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Implementation notes:
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- Keep the window borderless at all times (don’t toggle `styleMask`).
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- Add an overlay view inside the content container for chrome (stroke + subtle gradient/material).
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- Use an `NSTrackingArea` to fade the chrome in/out on `mouseEntered/mouseExited`.
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- Optionally show close/drag affordances only while hovered.
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## Agent API surface (proposed)
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Expose Canvas via the existing `clawdis-mac` → control socket → app routing so the agent can:
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- Show/hide the panel.
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- Navigate to a path (relative to the session root).
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- Evaluate JavaScript and optionally return results.
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- Query/modify DOM (helpers mirroring “dom query/all/attr/click/type/wait” patterns).
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- Capture a snapshot image of the current canvas view.
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- Optionally set panel placement (screen `x/y` + `width/height`) when showing/navigating.
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This should be modeled after `WebChatManager`/`WebChatWindowController` but targeting `clawdis-canvas://…` URLs.
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Related:
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- For “invoke the agent again from UI” flows, prefer the macOS deep link scheme (`clawdis://agent?...`) so *any* UI surface (Canvas, WebChat, native views) can trigger a new agent run. See `docs/clawdis-mac.md`.
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## Agent commands (current)
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`clawdis-mac` exposes Canvas via the control socket. For agent use, prefer `--json` so you can read the structured `CanvasShowResult` (including `status`).
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- `clawdis-mac canvas show [--session <key>] [--target <...>] [--x/--y/--width/--height]`
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- Local targets map into the session directory via the custom scheme (directory targets resolve `index.html|index.htm`).
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- If `/` has no index file, Canvas shows the built-in A2UI shell and returns `status: "a2uiShell"`.
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- `clawdis-mac canvas hide [--session <key>]`
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- `clawdis-mac canvas eval --js <code> [--session <key>]`
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- `clawdis-mac canvas snapshot [--out <path>] [--session <key>]`
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### Canvas A2UI
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Canvas includes a built-in **A2UI v0.8** renderer (Lit-based). The agent can drive it with JSONL **server→client protocol messages** (one JSON object per line):
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- `clawdis-mac canvas a2ui push --jsonl <path> [--session <key>]`
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- `clawdis-mac canvas a2ui reset [--session <key>]`
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`push` expects a JSONL file where **each line is a single JSON object** (parsed and forwarded to the in-page A2UI renderer).
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Minimal example (v0.8):
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```bash
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cat > /tmp/a2ui-v0.8.jsonl <<'EOF'
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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, `canvas a2ui push` works."},"usageHint":"body"}}}]}}
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{"beginRendering":{"surfaceId":"main","root":"root"}}
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EOF
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clawdis-mac canvas a2ui push --jsonl /tmp/a2ui-v0.8.jsonl --session main
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```
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Notes:
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- This does **not** support the A2UI v0.9 examples using `createSurface`.
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## Triggering agent runs from Canvas (deep links)
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Canvas can trigger new agent runs via the macOS app deep-link scheme:
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- `clawdis://agent?...`
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This is intentionally separate from `clawdis-canvas://…` (which is only for serving local Canvas files into the `WKWebView`).
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Suggested patterns:
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- HTML: render links/buttons that navigate to `clawdis://agent?message=...`.
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- JS: set `window.location.href = 'clawdis://agent?...'` for “run this now” actions.
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Implementation note (important):
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- In `WKWebView`, intercept `clawdis://…` navigations in `WKNavigationDelegate` and forward them to the app, e.g. by calling `DeepLinkHandler.shared.handle(url:)` and returning `.cancel` for the navigation.
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Safety:
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- `clawdis://agent` is disabled by default and must be enabled in **Clawdis → Settings → Debug** (“Allow URL scheme (agent)”).
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- Without a `key` query param, the app will prompt for confirmation before invoking the agent.
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## Security / guardrails
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Recommended defaults:
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- `WKWebsiteDataStore.nonPersistent()` for Canvas (ephemeral).
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- Navigation policy: allow only `clawdis-canvas://…` (and optionally `about:blank`); open `http/https` externally.
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- Scheme handler must prevent directory traversal: resolved file paths must stay under `<canvasRoot>/<session>/`.
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- Disable or tightly scope any JS bridge; prefer query-string/bootstrap config over `window.webkit.messageHandlers` for sensitive data.
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## Debugging
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Suggested debugging hooks:
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- Enable Web Inspector for Canvas builds (same approach as WebChat).
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- Log scheme requests + resolution decisions to OSLog (subsystem `com.steipete.clawdis`, category `Canvas`).
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- Provide a “copy canvas dir” action in debug settings to quickly reveal the session directory in Finder.
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