Show folder names immediately and refresh stale index sizes without walking the whole drive.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/Explorer.Application.Tests/BackgroundWorkPolicyTests.cs

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+using Explorer.Application;
+
+namespace Explorer.Application.Tests;
+
+public class BackgroundWorkPolicyTests
+{
+    private static BackgroundWorkInputs Idle(TimeSpan? idle = null, bool enabled = true, bool ac = true,
+        bool acOnly = true, bool foreground = false, bool runNow = false)
+        => new(
+            enabled,
+            TimeSpan.FromMinutes(10),
+            idle ?? TimeSpan.FromMinutes(12),
+            acOnly,
+            ac,
+            foreground,
+            runNow);
+
+    [Fact]
+    public void Below_threshold_stays_active()
+    {
+        var decision = BackgroundWorkPolicy.Evaluate(Idle(TimeSpan.FromMinutes(3)));
+        Assert.Equal(UserActivityState.Active, decision.Activity);
+        Assert.False(decision.MaintenanceAllowed);
+        Assert.Equal(MaintenanceSkipReason.BelowIdleThreshold, decision.SkipReason);
+    }
+
+    [Fact]
+    public void Idle_past_threshold_allows_maintenance()
+    {
+        var decision = BackgroundWorkPolicy.Evaluate(Idle());
+        Assert.Equal(UserActivityState.Idle, decision.Activity);
+        Assert.True(decision.MaintenanceAllowed);
+        Assert.Equal(MaintenanceSkipReason.None, decision.SkipReason);
+    }
+
+    [Fact]
+    public void Activity_resumes_and_blocks_maintenance()
+    {
+        var decision = BackgroundWorkPolicy.Evaluate(Idle(TimeSpan.Zero));
+        Assert.Equal(UserActivityState.Active, decision.Activity);
+        Assert.False(decision.MaintenanceAllowed);
+        Assert.Equal(MaintenanceSkipReason.UserActive, decision.SkipReason);
+    }
+
+    [Fact]
+    public void Foreground_jobs_block_even_when_idle()
+    {
+        var decision = BackgroundWorkPolicy.Evaluate(Idle(foreground: true));
+        Assert.False(decision.MaintenanceAllowed);
+        Assert.Equal(MaintenanceSkipReason.ForegroundOperations, decision.SkipReason);
+    }
+
+    [Fact]
+    public void Disabled_policy_never_allows()
+    {
+        var decision = BackgroundWorkPolicy.Evaluate(Idle(enabled: false));
+        Assert.False(decision.MaintenanceAllowed);
+        Assert.Equal(MaintenanceSkipReason.Disabled, decision.SkipReason);
+    }
+
+    [Fact]
+    public void Ac_only_skips_on_battery()
+    {
+        var decision = BackgroundWorkPolicy.Evaluate(Idle(ac: false, acOnly: true));
+        Assert.Equal(UserActivityState.Idle, decision.Activity);
+        Assert.False(decision.MaintenanceAllowed);
+        Assert.Equal(MaintenanceSkipReason.OnBattery, decision.SkipReason);
+    }
+
+    [Fact]
+    public void Ac_only_allows_on_ac()
+    {
+        var decision = BackgroundWorkPolicy.Evaluate(Idle(ac: true, acOnly: true));
+        Assert.True(decision.MaintenanceAllowed);
+    }
+
+    [Fact]
+    public void Run_now_bypasses_idle_and_battery_but_not_foreground()
+    {
+        var allowed = BackgroundWorkPolicy.Evaluate(Idle(TimeSpan.Zero, ac: false, runNow: true));
+        Assert.True(allowed.MaintenanceAllowed);
+
+        var blocked = BackgroundWorkPolicy.Evaluate(Idle(TimeSpan.Zero, foreground: true, runNow: true));
+        Assert.False(blocked.MaintenanceAllowed);
+        Assert.Equal(MaintenanceSkipReason.ForegroundOperations, blocked.SkipReason);
+    }
+}