fix(canvas): 5 UX polish fixes — error handling, a11y, loading state

1. ScheduleTab + ChannelsTab: wrap toggle/delete in try/catch with
   error feedback (was silently swallowing API failures)
2. MemoryTab: "+Add" button now auto-expands Advanced section
3. SidePanel: keyboard-navigated tabs scroll into view
4. TracesTab: emoji aria-hidden, env-var hint in <details>
5. page.tsx: show Spinner while hydrating instead of flash of EmptyState

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

canvas/src/app/page.tsx

@@ -1,9 +1,10 @@
 "use client";
 
-import { useEffect } from "react";
+import { useEffect, useState } from "react";
 import { Canvas } from "@/components/Canvas";
 import { Legend } from "@/components/Legend";
 import { CommunicationOverlay } from "@/components/CommunicationOverlay";
+import { Spinner } from "@/components/Spinner";
 import { connectSocket, disconnectSocket } from "@/store/socket";
 import { useCanvasStore } from "@/store/canvas";
 import { api } from "@/lib/api";
@@ -12,6 +13,7 @@ import type { WorkspaceData } from "@/store/socket";
 export default function Home() {
   const hydrationError = useCanvasStore((s) => s.hydrationError);
   const setHydrationError = useCanvasStore((s) => s.setHydrationError);
+  const [hydrating, setHydrating] = useState(true);
 
   useEffect(() => {
     connectSocket();
@@ -31,6 +33,8 @@ export default function Home() {
       useCanvasStore.getState().setHydrationError(
         err instanceof Error && err.message ? err.message : "Failed to load canvas"
       );
+    }).finally(() => {
+      setHydrating(false);
     });
 
     return () => {
@@ -38,6 +42,17 @@ export default function Home() {
     };
   }, []);
 
+  if (hydrating) {
+    return (
+      <div className="fixed inset-0 flex items-center justify-center bg-zinc-950">
+        <div className="flex flex-col items-center gap-3">
+          <Spinner size="lg" />
+          <span className="text-xs text-zinc-500">Loading canvas...</span>
+        </div>
+      </div>
+    );
+  }
+
   return (
     <>
       <Canvas />

canvas/src/components/SidePanel.tsx

@@ -173,7 +173,7 @@ export function SidePanel() {
           else if (e.key === "End") { e.preventDefault(); next = TABS.length - 1; }
           if (next !== null) {
             setPanelTab(TABS[next].id);
-            requestAnimationFrame(() => { document.getElementById(`tab-${TABS[next!].id}`)?.focus(); });
+            requestAnimationFrame(() => { const el = document.getElementById(`tab-${TABS[next!].id}`); el?.focus(); el?.scrollIntoView({ block: "nearest", inline: "nearest" }); });
           }
         }}
       >

canvas/src/components/tabs/ChannelsTab.tsx

@@ -141,19 +141,29 @@ export function ChannelsTab({ workspaceId }: Props) {
     }
   };
 
+  const [error, setError] = useState("");
+
   const handleToggle = async (ch: Channel) => {
-    await api.patch(`/workspaces/${workspaceId}/channels/${ch.id}`, {
-      enabled: !ch.enabled,
-    });
-    load();
+    try {
+      await api.patch(`/workspaces/${workspaceId}/channels/${ch.id}`, {
+        enabled: !ch.enabled,
+      });
+      load();
+    } catch (e: unknown) {
+      setError(e instanceof Error ? e.message : "Failed to toggle channel");
+    }
   };
 
   const confirmDelete = async () => {
     if (!pendingDelete) return;
     const ch = pendingDelete;
     setPendingDelete(null);
-    await api.del(`/workspaces/${workspaceId}/channels/${ch.id}`);
-    load();
+    try {
+      await api.del(`/workspaces/${workspaceId}/channels/${ch.id}`);
+      load();
+    } catch (e: unknown) {
+      setError(e instanceof Error ? e.message : "Failed to delete channel");
+    }
   };
 
   const handleTest = async (ch: Channel) => {
@@ -188,6 +198,12 @@ export function ChannelsTab({ workspaceId }: Props) {
         </button>
       </div>
 
+      {error && (
+        <div className="px-3 py-1.5 bg-red-900/30 border border-red-800 rounded text-xs text-red-400">
+          {error}
+        </div>
+      )}
+
       {/* Create form */}
       {showForm && (
         <div className="space-y-2 p-3 bg-zinc-800/40 rounded border border-zinc-700/50">

canvas/src/components/tabs/MemoryTab.tsx

@@ -219,7 +219,7 @@ export function MemoryTab({ workspaceId }: Props) {
               Refresh
             </button>
             <button
-              onClick={() => setShowAdd(!showAdd)}
+              onClick={() => { setShowAdd(!showAdd); if (!showAdd) setShowAdvanced(true); }}
               className="px-2 py-1 bg-blue-600 hover:bg-blue-500 text-[10px] rounded text-white"
             >
               + Add

canvas/src/components/tabs/ScheduleTab.tsx

@@ -126,15 +126,23 @@ export function ScheduleTab({ workspaceId }: Props) {
     if (!pendingDelete) return;
     const { id } = pendingDelete;
     setPendingDelete(null);
-    await api.del(`/workspaces/${workspaceId}/schedules/${id}`);
-    fetchSchedules();
+    try {
+      await api.del(`/workspaces/${workspaceId}/schedules/${id}`);
+      fetchSchedules();
+    } catch (e: unknown) {
+      setError(e instanceof Error ? e.message : "Failed to delete schedule");
+    }
   };
 
   const handleToggle = async (sched: Schedule) => {
-    await api.patch(`/workspaces/${workspaceId}/schedules/${sched.id}`, {
-      enabled: !sched.enabled,
-    });
-    fetchSchedules();
+    try {
+      await api.patch(`/workspaces/${workspaceId}/schedules/${sched.id}`, {
+        enabled: !sched.enabled,
+      });
+      fetchSchedules();
+    } catch (e: unknown) {
+      setError(e instanceof Error ? e.message : "Failed to toggle schedule");
+    }
   };
 
   const handleEdit = (sched: Schedule) => {

canvas/src/components/tabs/TracesTab.tsx

@@ -68,11 +68,14 @@ export function TracesTab({ workspaceId }: Props) {
 
       {traces.length === 0 && !error ? (
         <div className="text-center py-8">
-          <div className="text-2xl opacity-20 mb-2">📊</div>
+          <div className="text-2xl opacity-20 mb-2" aria-hidden="true">--</div>
           <p className="text-xs text-zinc-600">No traces yet</p>
-          <p className="text-[10px] text-zinc-700 mt-1">
-            Set LANGFUSE_HOST, LANGFUSE_PUBLIC_KEY, LANGFUSE_SECRET_KEY to enable tracing
-          </p>
+          <details className="mt-2 text-[10px] text-zinc-700">
+            <summary className="cursor-pointer text-zinc-500 hover:text-zinc-400">How to enable tracing</summary>
+            <p className="mt-1">
+              Set <code className="font-mono text-zinc-400">LANGFUSE_HOST</code>, <code className="font-mono text-zinc-400">LANGFUSE_PUBLIC_KEY</code>, <code className="font-mono text-zinc-400">LANGFUSE_SECRET_KEY</code> as workspace secrets to enable tracing.
+            </p>
+          </details>
         </div>
       ) : (
         <div className="space-y-1">