fix mutually canceling orbits

src/test/BehaviorSystemTest.cpp

@@ -1260,3 +1260,22 @@ TEST_CASE("OrbitMath: orbit sign follows the ship's tangential velocity",
     // Zero velocity (e.g. freshly spawned) → fallback +1.
     REQUIRE(OrbitMath::resolveOrbitSign(shipPos, center, QVector2D(0.0f, 0.0f)) == Approx(1.0f));
 }
+
+TEST_CASE("OrbitMath: orbit sense uses velocity relative to a moving center",
+          "[orbit]")
+{
+    const QVector2D center(0.0f, 0.0f);
+    const QVector2D shipPos(5.0f, 0.0f);  // radial points +x
+
+    // Two ships orbiting each other can translate in parallel: the ship and the
+    // center share the same velocity, so relative velocity cancels → fallback +1
+    // (both ships agree on the sign and break into a real mutual orbit).
+    const QVector2D sharedVelocity(0.0f, 3.0f);
+    REQUIRE(OrbitMath::resolveOrbitSign(shipPos, center, sharedVelocity, sharedVelocity)
+            == Approx(1.0f));
+
+    // A moving center's own motion is removed: the ship is stationary while the
+    // center drifts +y, so relative motion is -y → clockwise → -1.
+    REQUIRE(OrbitMath::resolveOrbitSign(shipPos, center, QVector2D(0.0f, 0.0f),
+                                        QVector2D(0.0f, 3.0f)) == Approx(-1.0f));
+}