test(ui): AcDream.UI.Abstractions unit tests (11 tests green)

Covers the pure-logic surface of commit 1:

  VitalsVMTests
    * HealthPercent reads from CombatState.GetHealthPercent
    * safe-default 1.0 when GUID unknown / not yet set / never updated
    * SetLocalPlayerGuid reroutes lookup to the new guid (no stale cache)
    * StaminaPercent / ManaPercent are null for D.2a scope
    * ctor throws ArgumentNullException on null CombatState

  PanelContextTests
    * record-struct fields round-trip
    * value-based equality

  NullCommandBusTests
    * Publish accepts any record type without throwing
    * Instance is a true singleton

csproj template mirrors AcDream.Core.Tests (xUnit 2.9.3, Test.Sdk 17.14.1,
runner 3.1.4, coverlet 6.0.4, implicit Using Xunit). References only
AcDream.UI.Abstractions — no runtime / GL dependency, tests run fast.

tests/AcDream.UI.Abstractions.Tests/VitalsVMTests.cs

@@ -0,0 +1,80 @@
+using AcDream.Core.Combat;
+using AcDream.UI.Abstractions.Panels.Vitals;
+
+namespace AcDream.UI.Abstractions.Tests;
+
+public sealed class VitalsVMTests
+{
+    [Fact]
+    public void HealthPercent_ReturnsCombatStateValue_AfterUpdateHealth()
+    {
+        var combat = new CombatState();
+        uint guid = 0x5000_0042u;
+        combat.OnUpdateHealth(guid, 0.42f);
+
+        var vm = new VitalsVM(combat);
+        vm.SetLocalPlayerGuid(guid);
+
+        Assert.Equal(0.42f, vm.HealthPercent, precision: 3);
+    }
+
+    [Fact]
+    public void HealthPercent_ReturnsOne_WhenGuidUnknown()
+    {
+        var combat = new CombatState();
+        var vm = new VitalsVM(combat);
+
+        // No SetLocalPlayerGuid call — defaults to 0 which CombatState has never seen.
+        Assert.Equal(1f, vm.HealthPercent);
+    }
+
+    [Fact]
+    public void HealthPercent_ReturnsOne_WhenGuidSetButNeverUpdated()
+    {
+        var combat = new CombatState();
+        var vm = new VitalsVM(combat);
+        vm.SetLocalPlayerGuid(0xDEAD_BEEFu);
+
+        Assert.Equal(1f, vm.HealthPercent);
+    }
+
+    [Fact]
+    public void StaminaPercent_IsNull_ForD2aScope()
+    {
+        // D.2a explicitly defers Stamina until LocalPlayerState + PlayerDescription
+        // wiring. When that arrives VitalsVM.StaminaPercent becomes non-null and
+        // VitalsPanel starts drawing the Stam bar automatically.
+        var vm = new VitalsVM(new CombatState());
+        Assert.Null(vm.StaminaPercent);
+    }
+
+    [Fact]
+    public void ManaPercent_IsNull_ForD2aScope()
+    {
+        var vm = new VitalsVM(new CombatState());
+        Assert.Null(vm.ManaPercent);
+    }
+
+    [Fact]
+    public void SetLocalPlayerGuid_ReroutesHealthLookup_WithoutStaleCache()
+    {
+        // Simulate the realistic GameWindow flow: VM is constructed pre-login
+        // with GUID=0, then SetLocalPlayerGuid is called at EnterWorld.
+        var combat = new CombatState();
+        uint playerGuid = 0x5003_E219u;
+        combat.OnUpdateHealth(playerGuid, 0.75f);
+
+        var vm = new VitalsVM(combat);
+        // Before SetLocalPlayerGuid — reads GUID=0 → returns safe 1.0.
+        Assert.Equal(1f, vm.HealthPercent);
+
+        vm.SetLocalPlayerGuid(playerGuid);
+        Assert.Equal(0.75f, vm.HealthPercent, precision: 3);
+    }
+
+    [Fact]
+    public void Constructor_ThrowsOnNullCombat()
+    {
+        Assert.Throws<ArgumentNullException>(() => new VitalsVM(null!));
+    }
+}