[AZ-365] Refactor C12: decompose RouteService.CreateRouteAsync

Extract RouteValidator (aggregating validator), RoutePointGraphBuilder
(point interpolation + sequence numbering), GeofenceGridCalculator
(NW/SE region centers), and RouteResponseMapper (entity -> DTO; also
used by GetRouteAsync, eliminating duplicate DTO assembly).

CreateRouteAsync shrinks 184 -> 52 LOC of orchestration. RouteService.cs
shrinks 295 -> 138 LOC overall. Validation aggregates all failures into
a single ArgumentException (AC-2); single-violation messages preserved
verbatim so existing RouteServiceTests pass unchanged. 28 new unit
tests for the four helpers (112/112 unit tests, smoke green).

Co-authored-by: Cursor <cursoragent@cursor.com>

SatelliteProvider.Tests/RouteValidatorTests.cs

@@ -0,0 +1,184 @@
+using FluentAssertions;
+using SatelliteProvider.Common.DTO;
+using SatelliteProvider.Services.RouteManagement;
+using SatelliteProvider.Tests.Fixtures;
+
+namespace SatelliteProvider.Tests;
+
+public class RouteValidatorTests
+{
+    private static CreateRouteRequest BuildValidRequest()
+    {
+        return new CreateRouteRequest
+        {
+            Id = Guid.NewGuid(),
+            Name = "valid-route",
+            Description = "test",
+            RegionSizeMeters = 500,
+            ZoomLevel = 18,
+            Points = TestCoordinates.Route.Route01Points
+                .Select(p => new RoutePoint { Latitude = p.Lat, Longitude = p.Lon })
+                .ToList(),
+        };
+    }
+
+    [Fact]
+    public void Validate_ValidRequest_DoesNotThrow_AZ365_AC2()
+    {
+        var sut = new RouteValidator();
+        var request = BuildValidRequest();
+
+        Action act = () => sut.Validate(request);
+
+        act.Should().NotThrow();
+    }
+
+    [Fact]
+    public void Validate_FewerThanTwoPoints_Throws()
+    {
+        var sut = new RouteValidator();
+        var request = BuildValidRequest();
+        request.Points = new List<RoutePoint> { new() { Latitude = 47.46, Longitude = 37.64 } };
+
+        Action act = () => sut.Validate(request);
+
+        act.Should().Throw<ArgumentException>().WithMessage("*at least 2 points*");
+    }
+
+    [Fact]
+    public void Validate_RegionSizeOutOfRange_Throws()
+    {
+        var sut = new RouteValidator();
+        var request = BuildValidRequest();
+        request.RegionSizeMeters = 50;
+
+        Action act = () => sut.Validate(request);
+
+        act.Should().Throw<ArgumentException>()
+            .WithMessage("*Region size must be between 100 and 10000*");
+    }
+
+    [Fact]
+    public void Validate_BlankName_Throws()
+    {
+        var sut = new RouteValidator();
+        var request = BuildValidRequest();
+        request.Name = "   ";
+
+        Action act = () => sut.Validate(request);
+
+        act.Should().Throw<ArgumentException>().WithMessage("*Route name is required*");
+    }
+
+    [Fact]
+    public void Validate_GeofencePolygonZeroZero_Throws()
+    {
+        var sut = new RouteValidator();
+        var request = BuildValidRequest();
+        request.Geofences = new Geofences
+        {
+            Polygons = new List<GeofencePolygon>
+            {
+                new() { NorthWest = new GeoPoint(0, 0), SouthEast = new GeoPoint(0, 0) },
+            },
+        };
+
+        Action act = () => sut.Validate(request);
+
+        act.Should().Throw<ArgumentException>()
+            .WithMessage("*coordinates cannot be (0,0)*");
+    }
+
+    [Fact]
+    public void Validate_GeofenceInvertedLatitudes_Throws()
+    {
+        var sut = new RouteValidator();
+        var request = BuildValidRequest();
+        request.Geofences = new Geofences
+        {
+            Polygons = new List<GeofencePolygon>
+            {
+                new()
+                {
+                    NorthWest = new GeoPoint(48.250, 37.370),
+                    SouthEast = new GeoPoint(48.280, 37.395),
+                },
+            },
+        };
+
+        Action act = () => sut.Validate(request);
+
+        act.Should().Throw<ArgumentException>().WithMessage("*northWest latitude*");
+    }
+
+    [Fact]
+    public void Validate_NullPolygonCorner_Throws()
+    {
+        var sut = new RouteValidator();
+        var request = BuildValidRequest();
+        request.Geofences = new Geofences
+        {
+            Polygons = new List<GeofencePolygon>
+            {
+                new() { NorthWest = null, SouthEast = new GeoPoint(48.260, 37.390) },
+            },
+        };
+
+        Action act = () => sut.Validate(request);
+
+        act.Should().Throw<ArgumentException>()
+            .WithMessage("*polygon coordinates are required*");
+    }
+
+    [Fact]
+    public void Validate_OutOfRangeLatitude_Throws()
+    {
+        var sut = new RouteValidator();
+        var request = BuildValidRequest();
+        request.Geofences = new Geofences
+        {
+            Polygons = new List<GeofencePolygon>
+            {
+                new()
+                {
+                    NorthWest = new GeoPoint(95, 37.370),
+                    SouthEast = new GeoPoint(48.265, 37.395),
+                },
+            },
+        };
+
+        Action act = () => sut.Validate(request);
+
+        act.Should().Throw<ArgumentException>()
+            .WithMessage("*coordinates must be valid*");
+    }
+
+    [Fact]
+    public void Validate_MultipleErrors_AggregatesIntoSingleException_AZ365_AC2()
+    {
+        var sut = new RouteValidator();
+        var request = BuildValidRequest();
+        request.Name = "";
+        request.RegionSizeMeters = 50;
+        request.Points = new List<RoutePoint>();
+
+        Action act = () => sut.Validate(request);
+
+        act.Should().Throw<ArgumentException>()
+            .Where(ex =>
+                ex.Message.Contains("at least 2 points")
+                && ex.Message.Contains("Region size must be between 100 and 10000")
+                && ex.Message.Contains("Route name is required"),
+                "AZ-365 AC-2: validator aggregates all failures into a single ArgumentException");
+    }
+
+    [Fact]
+    public void Validate_NullRequest_Throws()
+    {
+        var sut = new RouteValidator();
+
+        Action act = () => sut.Validate(null!);
+
+        act.Should().Throw<ArgumentNullException>();
+    }
+}