feat(render): Phase A8.F — PhysicsCameraCollisionProbe (swept-sphere eye via ResolveWithTransition)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/AcDream.App.Tests/Rendering/PhysicsCameraCollisionProbeTests.cs

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+using System.Numerics;
+using AcDream.App.Rendering;
+using AcDream.Core.Physics;
+using Xunit;
+
+namespace AcDream.App.Tests.Rendering;
+
+public class PhysicsCameraCollisionProbeTests
+{
+    // The probe must convert the desired eye path (where the SPHERE CENTER
+    // should travel) into the foot-capsule path InitPath expects (which offsets
+    // sphere0 up by radius), then invert it on the result. Verify the round trip.
+    [Fact]
+    public void SpherePathOffset_RoundTrips()
+    {
+        var p = new Vector3(10f, 20f, 30f);
+        const float r = 0.3f;
+
+        var path = PhysicsCameraCollisionProbe.ToSpherePath(p, r);
+        Assert.Equal(p.Z - r, path.Z, 5);
+        Assert.Equal(p.X, path.X, 5);
+        Assert.Equal(p.Y, path.Y, 5);
+
+        var back = PhysicsCameraCollisionProbe.FromSpherePath(path, r);
+        Assert.Equal(p.X, back.X, 5);
+        Assert.Equal(p.Y, back.Y, 5);
+        Assert.Equal(p.Z, back.Z, 5);
+    }
+
+    // cellId == 0 means "no starting cell" — the probe must short-circuit and
+    // return the desired eye without touching the engine.
+    [Fact]
+    public void SweepEye_NoStartingCell_ReturnsDesiredEyeUnchanged()
+    {
+        var probe = new PhysicsCameraCollisionProbe(new PhysicsEngine());
+        var pivot = new Vector3(0f, 0f, 1.5f);
+        var eye   = new Vector3(-2f, 0f, 2.2f);
+
+        var result = probe.SweepEye(pivot, eye, cellId: 0, selfEntityId: 0);
+
+        Assert.Equal(eye, result);
+    }
+}