refactor: node tools and canvas host url

docs/mac/canvas.md

@@ -123,6 +123,8 @@ clawdis canvas a2ui push --jsonl /tmp/a2ui-v0.8.jsonl --node <id>
 Notes:
 - This does **not** support the A2UI v0.9 examples using `createSurface`.
 - A2UI **fails** if the Gateway canvas host is unreachable (no local fallback).
+- `canvas a2ui push` validates JSONL (line numbers on errors) and rejects v0.9 payloads.
+- Quick smoke: `clawdis canvas a2ui push --text "Hello from A2UI"` renders a minimal v0.8 view.
 
 ## Triggering agent runs from Canvas (deep links)