The feed doesn't say "Empty" before its persona is known

On opening, the feed showed "Empty" until the session had been read and a persona chosen, then loaded: a flash of a
wrong answer on every start (and the end-to-end sign-in took it for a loaded feed). CascadingState says once the session
has been read (IsSessionLoaded), and until then a feed with no persona yet is loading; a login without any persona still
gets its empty feed. The persona-switch test waits for the sibling's home read with another token than the first
persona's, instead of any home read after the switch was asked for.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

LayerComponents/CascadingState.razor

@@ -27,6 +27,8 @@
 	public PublicCacheData PublicCacheData { get; private set; } = new();
 	/// <summary>Whether a root is signed in (its JWT is still valid).</summary>
 	public bool IsSignedIn { get; private set; }
+	/// <summary>The session has been read once: from then on a null PersonaId means the login has no persona, not "not yet".</summary>
+	public bool IsSessionLoaded { get; private set; }
 	/// <summary>The root's login name, shown to its owner only.</summary>
 	public string RootUserName { get; private set; }
 	/// <summary>The root's personas.</summary>
@@ -93,6 +95,7 @@
 		if (!IsSignedIn)
 		{
 			ClearSession();
+			IsSessionLoaded = true;
 			StateHasChanged();
 			return;
 		}
@@ -105,10 +108,12 @@
 		{
 			PersonaId = null;
 			Persona = null;
+			IsSessionLoaded = true;
 			StateHasChanged();
 			return;
 		}
 
+		IsSessionLoaded = true;
 		await SwitchPersona(personaId, cancellationToken);
 	}