Fix Location hash stability

Root cause: Location.GetHashCode accidentally combined latitude with itself, so longitude never influenced the hash for this public value-like core type.

Author: niemyjski

AGENTS.md

@@ -68,6 +68,7 @@ samples/
 - Use modern C# features where the target frameworks support them
 - Follow SOLID, DRY principles; remove unused code and parameters
 - Clear, descriptive naming; prefer explicit over clever
+- For existing public value-like types, prefer additive equality fixes over record conversions unless an API shape change is explicitly intended
 - Handle cancellation tokens properly: pass through call chains
 - Always dispose resources: use `using` statements
 

src/Geocoding.Core/Location.cs

@@ -139,7 +139,10 @@ public bool Equals(Location? coor)
     /// <returns>A hash code for this location.</returns>
     public override int GetHashCode()
     {
-        return Latitude.GetHashCode() ^ Latitude.GetHashCode();
+        unchecked
+        {
+            return (Latitude.GetHashCode() * 397) ^ Longitude.GetHashCode();
+        }
     }
 
     /// <summary>

test/Geocoding.Tests/LocationTest.cs

@@ -31,6 +31,17 @@ public void Equals_SameCoordinates_ReturnsTrue()
         Assert.Equal(loc1.GetHashCode(), loc2.GetHashCode());
     }
 
+    [Fact]
+    public void GetHashCode_IncludesLongitudeHash()
+    {
+        // Arrange
+        Location loc = new Location(85.6789, 92.4517);
+        int expectedHashCode = unchecked((loc.Latitude.GetHashCode() * 397) ^ loc.Longitude.GetHashCode());
+
+        // Assert
+        Assert.Equal(expectedHashCode, loc.GetHashCode());
+    }
+
     [Fact]
     public void DistanceBetween_TwoLocations_ReturnsSameDistanceBothDirections()
     {