refactor: serve canvas host on gateway port

docs/refactor/canvas-a2ui.md

@@ -16,9 +16,10 @@ Status: Implemented · Date: 2025-12-20
 - A2UI renders only when the **Gateway is reachable** (acceptable failure mode).
 
 ## Decision
-All A2UI HTML/JS assets are **served by the Gateway’s Canvas host** over HTTP.
-Nodes (mac/iOS/Android) **navigate to the Gateway URL** before applying A2UI
-messages. No local custom-scheme or bundled fallback remains.
+All A2UI HTML/JS assets are **served by the Gateway HTTP server** (single port,
+same as the Gateway WebSocket). Nodes (mac/iOS/Android) **navigate to the
+Gateway URL** before applying A2UI messages. No local custom-scheme or bundled
+fallback remains.
 
 ## Why
 - One source of truth (TS) for A2UI rendering.
@@ -36,14 +37,16 @@ messages. No local custom-scheme or bundled fallback remains.
 ## Gateway changes
 
 ### Serve A2UI assets
-Add A2UI HTML/JS to the Gateway Canvas host, e.g.:
+Add A2UI HTML/JS to the Gateway Canvas host (same HTTP server as the Gateway
+WS), e.g.:
 
 ```
 /__clawdis__/a2ui/           -> index.html
 /__clawdis__/a2ui/a2ui.bundle.js -> bundled A2UI runtime
 ```
 
-Use the existing Canvas host server (`src/canvas-host/server.ts`) to serve these
+Serve Canvas files at `/__clawdis__/canvas/` and A2UI at `/__clawdis__/a2ui/`.
+Use the shared Canvas host handler (`src/canvas-host/server.ts`) to serve these
 assets and inject the action bridge + live reload if desired.
 
 ### Derive HTTP host from WebSocket
@@ -81,6 +84,7 @@ If `canvasHostUrl` is missing or unreachable:
 1) Gateway
    - Add A2UI assets under `src/canvas-host/`.
    - Serve them at `/__clawdis__/a2ui/` (align with existing naming).
+   - Serve Canvas files at `/__clawdis__/canvas/` on the Gateway port.
    - Expose `canvasHostUrl` in handshake + bridge hello payloads.
 2) Node runtimes
    - Update `canvas.a2ui.*` to navigate to `canvasHostUrl`.