test(core/slice-1): FadeAlpha endpoint + monotonicity + ShowTunnel/ShowPleaseWait coverage

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/AcDream.Core.Tests/World/TeleportAnimSequencerTests.cs

@@ -236,4 +236,109 @@ public sealed class TeleportAnimSequencerTests
         Assert.False(seq.IsActive);
         Assert.Contains(TeleportAnimEvent.FireLoginComplete, evts);
     }
+
+    // --- Task 1.4: FadeAlpha endpoints and monotonicity ---
+
+    [Fact]
+    public void FadeAlpha_IsZeroAtStart_OfWorldFadeOut()
+    {
+        var seq = new TeleportAnimSequencer();
+        seq.Begin(TeleportEntryKind.Logout);
+        var (snap, _) = seq.Tick(dt: 0f, worldReady: false);
+        // At elapsed=0 in WorldFadeOut: smoothstep(0)=0 => alpha=0 (world fully visible).
+        Assert.Equal(0f, snap.FadeAlpha, precision: 4);
+    }
+
+    [Fact]
+    public void FadeAlpha_IsOneAtEnd_OfWorldFadeOut()
+    {
+        var seq = new TeleportAnimSequencer();
+        seq.Begin(TeleportEntryKind.Logout);
+        seq.Tick(0f, worldReady: false); // consume enter-sound tick, elapsed≈0
+
+        // Drive to just BEFORE the transition (so we're still in WorldFadeOut)
+        DriveSeconds(seq, TeleportAnimSequencer.FadeTime - 0.02f, worldReady: false);
+        Assert.Equal(TeleportAnimState.WorldFadeOut, seq.State);
+
+        var (snap, _) = seq.Tick(0f, worldReady: false);
+        // smoothstep(clamp((1.0-0.02)/1.0,0,1)) should be close to 1
+        Assert.True(snap.FadeAlpha > 0.95f, $"Expected FadeAlpha near 1, got {snap.FadeAlpha}");
+    }
+
+    [Fact]
+    public void FadeAlpha_IsMonotonicallyIncreasing_DuringWorldFadeOut()
+    {
+        var seq = new TeleportAnimSequencer();
+        seq.Begin(TeleportEntryKind.Logout);
+        seq.Tick(0f, worldReady: false);
+
+        float prev = -1f;
+        // Sample 50 steps within FadeTime
+        float step = TeleportAnimSequencer.FadeTime / 50f;
+        for (int i = 0; i < 48; i++) // stop before transition
+        {
+            var (snap, _) = seq.Tick(step, worldReady: false);
+            if (seq.State != TeleportAnimState.WorldFadeOut) break;
+            Assert.True(snap.FadeAlpha >= prev - 0.001f,
+                $"Alpha decreased: {prev} -> {snap.FadeAlpha} at step {i}");
+            prev = snap.FadeAlpha;
+        }
+    }
+
+    [Fact]
+    public void FadeAlpha_IsZero_DuringTunnelStates()
+    {
+        var seq = new TeleportAnimSequencer();
+        seq.Begin(TeleportEntryKind.Portal);
+        seq.Tick(0f, worldReady: false);
+
+        // In Tunnel state, overlay alpha should be 0 (the tunnel viewport is shown; no alpha quad needed)
+        var (snap, _) = seq.Tick(0.016f, worldReady: false);
+        Assert.Equal(TeleportAnimState.Tunnel, seq.State);
+        Assert.Equal(0f, snap.FadeAlpha);
+    }
+
+    [Fact]
+    public void ShowTunnel_TrueInTunnelFamilyStates_FalseOtherwise()
+    {
+        // Logout path: WorldFadeOut -> TunnelFadeIn -> Tunnel -> TunnelContinue -> TunnelFadeOut -> WorldFadeIn -> Off
+        var seq = new TeleportAnimSequencer();
+        seq.Begin(TeleportEntryKind.Logout);
+        seq.Tick(0f, worldReady: false);
+
+        // WorldFadeOut: ShowTunnel = false
+        var (snap, _) = seq.Tick(0.016f, worldReady: false);
+        Assert.Equal(TeleportAnimState.WorldFadeOut, seq.State);
+        Assert.False(snap.ShowTunnel);
+
+        // Advance to TunnelFadeIn
+        DriveSeconds(seq, TeleportAnimSequencer.FadeTime, worldReady: false);
+        Assert.Equal(TeleportAnimState.TunnelFadeIn, seq.State);
+        var (snap2, _) = seq.Tick(0f, worldReady: false);
+        Assert.True(snap2.ShowTunnel);
+
+        // Advance to Tunnel
+        DriveSeconds(seq, TeleportAnimSequencer.FadeTime, worldReady: false);
+        Assert.Equal(TeleportAnimState.Tunnel, seq.State);
+        var (snap3, _) = seq.Tick(0f, worldReady: false);
+        Assert.True(snap3.ShowTunnel);
+    }
+
+    [Fact]
+    public void ShowPleaseWait_TrueOnlyInTunnelContinue()
+    {
+        var seq = new TeleportAnimSequencer();
+        seq.Begin(TeleportEntryKind.Portal);
+        seq.Tick(0f, worldReady: false);
+
+        // Tunnel: ShowPleaseWait false
+        var (snap1, _) = seq.Tick(0.016f, worldReady: false);
+        Assert.Equal(TeleportAnimState.Tunnel, seq.State);
+        Assert.False(snap1.ShowPleaseWait);
+
+        // Advance to TunnelContinue
+        var (snap2, _) = seq.Tick(0.016f, worldReady: true);
+        Assert.Equal(TeleportAnimState.TunnelContinue, seq.State);
+        Assert.True(snap2.ShowPleaseWait);
+    }
 }