fix(central-ui): resolve CentralUI-020..025 — auth-ping idle logout, DebugView race, push-handler disposal guard, JS-interop catch narrowing, claim-constant helper, SessionExpiry tests

src/ScadaLink.CentralUI/Auth/ClaimsPrincipalExtensions.cs

@@ -0,0 +1,43 @@
+using System.Security.Claims;
+using Microsoft.AspNetCore.Components.Authorization;
+using ScadaLink.Security;
+
+namespace ScadaLink.CentralUI.Auth;
+
+/// <summary>
+/// Claim-lookup helpers for the Central UI. CentralUI-024: claim types are owned
+/// by <see cref="JwtTokenService"/> (the single source of truth). These helpers
+/// resolve them through the <c>JwtTokenService</c> constants so a rename there
+/// propagates here instead of silently breaking ten copy-pasted call sites.
+/// </summary>
+public static class ClaimsPrincipalExtensions
+{
+    /// <summary>Fallback returned when no username claim is present.</summary>
+    public const string UnknownUser = "unknown";
+
+    /// <summary>
+    /// The audit username for <paramref name="principal"/>, or
+    /// <see cref="UnknownUser"/> when the claim is absent.
+    /// </summary>
+    public static string GetUsername(this ClaimsPrincipal principal)
+        => principal.FindFirst(JwtTokenService.UsernameClaimType)?.Value ?? UnknownUser;
+
+    /// <summary>
+    /// The display name for <paramref name="principal"/>, or <c>null</c> when
+    /// the claim is absent.
+    /// </summary>
+    public static string? GetDisplayName(this ClaimsPrincipal principal)
+        => principal.FindFirst(JwtTokenService.DisplayNameClaimType)?.Value;
+
+    /// <summary>
+    /// Resolves the current user's audit username from the auth state provider.
+    /// Replaces the <c>GetCurrentUserAsync</c> helper that was copy-pasted into
+    /// ten components (CentralUI-024).
+    /// </summary>
+    public static async Task<string> GetCurrentUsernameAsync(
+        this AuthenticationStateProvider authStateProvider)
+    {
+        var authState = await authStateProvider.GetAuthenticationStateAsync();
+        return authState.User.GetUsername();
+    }
+}