Complete portable planetary presentation contracts

tests/CultMath.Tests/PlanetaryMapTileEncodingTests.cs

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+using System.IO;
+using Xunit;
+
+namespace CultMath.Tests;
+
+public sealed class PlanetaryMapTileEncodingTests
+{
+    [Fact]
+    public void BinaryTileRoundTripsIdentityValidityAndSurfaceEvidence()
+    {
+        var field = PlanetaryFieldDefinition.Create(5, 10, 3, AdvancedErosionParameters.Default);
+        var layout = new PlanetaryMapTileLayout(new(PlanetaryProjectionKind.EqualEarth), 1, 1, 0, 5, 1);
+        var key = new PlanetaryMapTileKey(field.FieldVersion, 2, 17, layout, PlanetaryQueryScale.AtFootprint(0.25f, 0.1f));
+        var tile = PlanetaryMapTileBaker.Bake(field, key, new FlatField());
+        using var bytes = new MemoryStream();
+        PlanetaryMapTileEncoding.Write(bytes, tile, leaveOpen: true);
+        bytes.Position = 0;
+        var decoded = PlanetaryMapTileEncoding.Read(bytes);
+
+        Assert.Equal(tile.Key, decoded.Key);
+        Assert.Equal(tile.Validity, decoded.Validity);
+        for (var i = 0; i < tile.Samples.Length; i++)
+            if (tile.Validity[i]) Assert.Equal(tile.Samples[i], decoded.Samples[i]);
+    }
+
+    [Fact]
+    public void DecoderRejectsForeignMagicAndVersions()
+    {
+        Assert.Throws<InvalidDataException>(() => PlanetaryMapTileEncoding.Read(new MemoryStream(new byte[] { 1, 2, 3, 4, 1, 0, 0, 0 })));
+        var bytes = new byte[] { (byte)'C', (byte)'M', (byte)'P', (byte)'T', 99, 0, 0, 0 };
+        Assert.Throws<InvalidDataException>(() => PlanetaryMapTileEncoding.Read(new MemoryStream(bytes)));
+    }
+
+    [Fact]
+    public void DecoderRejectsTrailingBytes()
+    {
+        var field = PlanetaryFieldDefinition.Create(2, 1, 0, AdvancedErosionParameters.Default);
+        var layout = new PlanetaryMapTileLayout(new(PlanetaryProjectionKind.Equirectangular), 0, 0, 0, 2, 0);
+        var key = new PlanetaryMapTileKey(field.FieldVersion, 1, 0, layout, PlanetaryQueryScale.AtFootprint(1));
+        var tile = PlanetaryMapTileBaker.Bake(field, key, new FlatField());
+        using var bytes = new MemoryStream();
+        PlanetaryMapTileEncoding.Write(bytes, tile, leaveOpen: true);
+        bytes.WriteByte(0xff);
+        bytes.Position = 0;
+        Assert.Throws<InvalidDataException>(() => PlanetaryMapTileEncoding.Read(bytes));
+    }
+
+    private readonly struct FlatField : IPlanetaryBaseField
+    {
+        public PlanetaryBaseFieldSample Sample(float3 direction) => new(0, float3.zero, 0, float3.zero, 0);
+    }
+}