feat(net): #13 heuristic inventory locator after gameplay_options blob

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/AcDream.Core.Net/Messages/PlayerDescriptionParser.cs

@@ -402,7 +402,17 @@ public static class PlayerDescriptionParser
                     if (optionFlags.HasFlag(CharacterOptionDataFlag.CharacterOptions2))
                         options2 = ReadU32(payload, ref pos);
 
-                    if (!optionFlags.HasFlag(CharacterOptionDataFlag.GameplayOptions))
+                    if (optionFlags.HasFlag(CharacterOptionDataFlag.GameplayOptions))
+                    {
+                        int gameplayStart = pos;
+                        if (TryHeuristicInventoryStart(payload, gameplayStart, out int invStart, out int end,
+                                inventory, equipped))
+                        {
+                            gameplayOptions = payload.Slice(gameplayStart, invStart - gameplayStart).ToArray();
+                            pos = end;
+                        }
+                    }
+                    else
                     {
                         // Strict path: inventory + equipped follow directly.
                         TryUnpackInventoryStrict(payload, ref pos, inventory, equipped);
@@ -760,6 +770,43 @@ public static class PlayerDescriptionParser
         return true;
     }
 
+    /// <summary>4-byte-aligned forward scan from <paramref name="start"/>
+    /// looking for the first offset where <c>TryUnpackInventoryStrict</c>
+    /// consumes exactly to end-of-buffer. Mirrors holtburger
+    /// <c>find_inventory_start_after_gameplay_options</c> in events.rs:195-218.</summary>
+    private static bool TryHeuristicInventoryStart(
+        ReadOnlySpan<byte> src, int start,
+        out int invStart, out int end,
+        List<InventoryEntry> inventory, List<EquippedEntry> equipped)
+    {
+        invStart = end = 0;
+        inventory.Clear();
+        equipped.Clear();
+        if (start + 8 > src.Length) return false;
+
+        int candidate = start;
+        int misalign = candidate & 3;
+        if (misalign != 0) candidate += 4 - misalign;
+
+        int last = src.Length - 8;
+        while (candidate <= last)
+        {
+            int tmp = candidate;
+            var tmpInv = new List<InventoryEntry>();
+            var tmpEq  = new List<EquippedEntry>();
+            if (TryUnpackInventoryStrict(src, ref tmp, tmpInv, tmpEq) && tmp == src.Length)
+            {
+                invStart = candidate;
+                end = tmp;
+                inventory.AddRange(tmpInv);
+                equipped.AddRange(tmpEq);
+                return true;
+            }
+            candidate += 4;
+        }
+        return false;
+    }
+
     private static ushort ReadU16(ReadOnlySpan<byte> src, ref int pos)
     {
         if (src.Length - pos < 2) throw new FormatException("truncated u16");

tests/AcDream.Core.Net.Tests/PlayerDescriptionParserTests.cs

@@ -663,4 +663,46 @@ public sealed class PlayerDescriptionParserTests
         Assert.Equal(0x00000200u, parsed.Value.Equipped[0].EquipLocation);
         Assert.Equal(1u, parsed.Value.Equipped[0].Priority);
     }
+
+    [Fact]
+    public void TryParse_TrailerGameplayOptions_HeuristicLocatesInventoryStart()
+    {
+        var sb = new MemoryStream();
+        using var writer = new BinaryWriter(sb);
+        writer.Write(0u);               // propertyFlags
+        writer.Write(0x52u);             // weenieType
+        writer.Write(0x201u);            // ATTRIBUTE | ENCHANTMENT
+        writer.Write(1u);                // has_health
+        writer.Write(0u);                // empty attribute_flags
+        writer.Write(0u);                // empty enchantment mask
+
+        // option_flags = GAMEPLAY_OPTIONS (0x200)
+        writer.Write(0x200u);
+        writer.Write(0u);                // options1
+        writer.Write(0u);                // legacy hotbar count=0
+        writer.Write(0u);                // spellbook_filters
+
+        // 16 bytes of opaque gameplay_options blob — values that *almost* look
+        // like an inventory header but fail validation (wtype > 2 or count too
+        // big), forcing the heuristic to walk past them.
+        writer.Write(0xDEADBEEFu);       // looks like inv_count = 0xDEADBEEF (> 10_000) — rejected
+        writer.Write(0xCAFEBABEu);
+        writer.Write(0x12345678u);
+        writer.Write(0x87654321u);
+
+        // Real inventory: 1 entry, then equipped: 1 entry — must consume to EOF.
+        writer.Write(1u);
+        writer.Write(0x50000200u); writer.Write(0u);
+        writer.Write(1u);
+        writer.Write(0x50000300u); writer.Write(0x00000200u); writer.Write(1u);
+
+        var parsed = PlayerDescriptionParser.TryParse(sb.ToArray());
+
+        Assert.NotNull(parsed);
+        Assert.Single(parsed!.Value.Inventory);
+        Assert.Equal(0x50000200u, parsed.Value.Inventory[0].Guid);
+        Assert.Single(parsed.Value.Equipped);
+        Assert.Equal(0x50000300u, parsed.Value.Equipped[0].Guid);
+        Assert.Equal(16, parsed.Value.GameplayOptions.Length);
+    }
 }