fix: Handle expansion flag migration correctly

Author: ResurrectedTrader

src/D2SSharp.Tests/IntegrationTests.cs

@@ -489,6 +489,45 @@ public void Convert_99_To_105_RoundTrip()
         Assert.Equal(save105.Character.Class, restored.Character.Class);
     }
 
+    /// <summary>
+    /// Tests that expansion sections (MercItems, IronGolem) survive v99→v105→v99 conversion.
+    /// The v104+ format moves the Expansion flag from CharacterFlags to GameVersion;
+    /// the reader/writer must use GameVersion for v104+ to avoid losing expansion sections.
+    /// </summary>
+    [Fact]
+    public void Convert_99_To_105_PreservesExpansionSections()
+    {
+        var data = File.ReadAllBytes(Path.Combine("Resources", "99", "Roka.d2s"));
+        var original = D2Save.Read(data);
+
+        Assert.True(original.Character.Flags.HasFlag(Enums.CharacterFlags.Expansion), "Source save should be expansion");
+        Assert.NotNull(original.MercItems);
+        Assert.NotNull(original.IronGolem);
+        _output.WriteLine($"Original v{original.Version}: Expansion={original.Character.Flags.HasFlag(Enums.CharacterFlags.Expansion)}, MercItems={original.MercItems != null}, IronGolem={original.IronGolem != null}");
+
+        // Convert to v105
+        var buffer105 = new byte[data.Length * 2];
+        int written105 = original.Write(buffer105, targetVersion: 105);
+
+        // Read back — must still have expansion sections
+        var save105 = D2Save.Read(buffer105.AsSpan(0, written105));
+        Assert.Equal(Enums.GameVersion.Expansion, save105.Character.Preview.GameVersion);
+        Assert.NotNull(save105.MercItems);
+        Assert.NotNull(save105.IronGolem);
+        _output.WriteLine($"v105: GameVersion={save105.Character.Preview.GameVersion}, MercItems={save105.MercItems != null}, IronGolem={save105.IronGolem != null}");
+
+        // Convert back to v99
+        var buffer99 = new byte[written105 * 2];
+        int written99 = save105.Write(buffer99, targetVersion: 99);
+
+        // Read back — must still have expansion sections and flag restored
+        var restored = D2Save.Read(buffer99.AsSpan(0, written99));
+        Assert.True(restored.Character.Flags.HasFlag(Enums.CharacterFlags.Expansion), "Restored save should have Expansion flag");
+        Assert.NotNull(restored.MercItems);
+        Assert.NotNull(restored.IronGolem);
+        _output.WriteLine($"Restored v{restored.Version}: Expansion={restored.Character.Flags.HasFlag(Enums.CharacterFlags.Expansion)}, MercItems={restored.MercItems != null}, IronGolem={restored.IronGolem != null}");
+    }
+
     /// <summary>
     /// Tests round-trip for the modern v105 shared stash file with chronicle and advanced stash tabs.
     /// </summary>

src/D2SSharp/Model/D2Save.cs

@@ -12,8 +12,8 @@ public partial class D2Save
     /// <summary>File magic value: 0xAA55AA55</summary>
     public const uint Magic = 0xAA55AA55;
 
-    /// <summary>Current save version (96 for 1.10+).</summary>
-    public const uint CurrentVersion = 96;
+    /// <summary>Current save version (105 for D2R 3.x).</summary>
+    public const uint CurrentVersion = 105;
 
     /// <summary>Save file version.</summary>
     public uint Version { get; set; } = CurrentVersion;
@@ -104,7 +104,7 @@ public static D2Save Read(ReadOnlySpan<byte> data, IExternalData externalData)
         save.Corpses = CorpseSection.Read(ref reader, externalData, save.Version);
 
         // Expansion-only sections
-        if (save.Character.Flags.HasFlag(CharacterFlags.Expansion))
+        if (save.IsExpansion(save.Version))
         {
             save.MercItems = MercItemsSection.Read(ref reader, externalData, save.Character.MercData.HasMerc, save.Version);
             save.IronGolem = IronGolemSection.Read(ref reader, externalData, save.Version);
@@ -171,7 +171,7 @@ public int Write(Span<byte> buffer, IExternalData externalData, uint? targetVers
         Corpses.Write(ref writer, externalData, Version);
 
         // Expansion-only sections
-        if (Character.Flags.HasFlag(CharacterFlags.Expansion))
+        if (IsExpansion(Version))
         {
             (MercItems ?? new MercItemsSection()).Write(ref writer, externalData, Character.MercData.HasMerc, Version);
             (IronGolem ?? new IronGolemSection()).Write(ref writer, externalData, Version);
@@ -227,7 +227,7 @@ public int EstimateSize()
         }
 
         // Expansion sections
-        if (Character.Flags.HasFlag(CharacterFlags.Expansion))
+        if (IsExpansion(Version))
         {
             // Merc items
             size += 4 + CountItemsRecursive(MercItems?.Items) * 200;
@@ -283,6 +283,13 @@ public static bool VerifyChecksum(ReadOnlySpan<byte> data)
         return ChecksumCalculator.Verify(data);
     }
 
+    /// <summary>
+    /// Returns true if this save is an expansion save, checking GameVersion for v104+ or CharacterFlags for older versions.
+    /// </summary>
+    private bool IsExpansion(uint version) => version >= 104
+        ? Character.Preview.GameVersion > GameVersion.Classic
+        : Character.Flags.HasFlag(CharacterFlags.Expansion);
+
     /// <summary>
     /// Prepares the save data for writing to a specific version format.
     /// Handles conversion between 1.14 (version 96) and D2R (version 97+) formats,
@@ -381,10 +388,11 @@ private void Convert103To104()
         }
 
         // GuildEmblemColor: keep low byte (uint -> byte)
-        Character.Preview.GuildEmblemColor = Character.Preview.GuildEmblemColor & 0xFF;
+        Character.Preview.GuildEmblemColor &= 0xFF;
 
         // GameVersion: derive from CharacterFlags
         Character.Preview.GameVersion = Character.Flags.HasFlag(CharacterFlags.Expansion) ? GameVersion.Expansion : GameVersion.Classic;
+        Character.Flags &= ~CharacterFlags.Expansion;
 
         // SaveTimes/Experiences: slots 0-1 already populated, 2-5 remain zero (default)
     }
@@ -402,6 +410,11 @@ private void Convert104To103()
                 : Character.Preview.Name;
         }
 
+        if (Character.Preview.GameVersion > GameVersion.Classic)
+        {
+            Character.Flags |= CharacterFlags.Expansion;
+        }
+
         // GuildEmblemColor: byte -> uint (zero-extend, already correct)
 
         // SaveTimes/Experiences: only [0] and [1] are used in old format