Switch to net9.0; improve AcBinary diagnostics & chunk fallback

- Change target framework to net9.0 in AyCode.Core.targets.
- Add DEBUG-only property access diagnostics to AcBinarySerializer for better error reporting.
- Update AcBinaryHubProtocol to dispose chunk state and retry normal parse on unknown bytes, improving resilience after serialization failures.
- Update comments to clarify new logic and rationale.

AyCode.Core.targets

@@ -7,7 +7,7 @@
 		<!--<GitBranch>$([System.IO.File]::ReadAlltext('$(MsBuildThisFileDirectory)\.git\HEAD').Replace('ref: refs/heads/', '').Trim())</GitBranch>
 		<_ProjectName>$(GitBranch)</_ProjectName>-->
 
-		<TargetFramework Condition="'$(TargetFramework)' == ''">net10.0</TargetFramework>
+		<TargetFramework Condition="'$(TargetFramework)' == ''">net9.0</TargetFramework>
 		<ImplicitUsings>enable</ImplicitUsings>
 		<Nullable>enable</Nullable>
 

AyCode.Core/Serializers/Binaries/AcBinarySerializer.cs

@@ -6,6 +6,7 @@ using System.Collections.Concurrent;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq.Expressions;
+using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Text;
@@ -1965,7 +1966,12 @@ public static partial class AcBinarySerializer
                     // Use pre-cached wrapper, fallback to GetWrapper on miss/polymorphism
                     // Set interning eligibility for string collection elements
                     context.StringInternEligible = prop.IsStringCollectionProperty && prop.UseStringPropertyInterning(context.InternBit);
+
+                    #if DEBUG
+                    var value = GetPropertyValueWithDiagnostics(obj, prop);
+                    #else
                     var value = prop.GetValue(obj);
+                    #endif
 
                     // SKIP marker only for null (reference types)
                     // Empty string, empty collections, etc. are valid values and must be written!
@@ -2004,6 +2010,26 @@ public static partial class AcBinarySerializer
         }
     }
 
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static object? GetPropertyValueWithDiagnostics(object source, BinaryPropertyAccessor property)
+    {
+        try
+        {
+            return property.GetValue(source);
+        }
+        catch (Exception ex) when (ex is NullReferenceException || ex is TargetInvocationException)
+        {
+            var sourceType = source.GetType().FullName ?? source.GetType().Name;
+            var propertyName = property.Name;
+            var declaredType = property.PropertyType?.FullName ?? "<unknown>";
+
+            throw new InvalidOperationException(
+                $"AcBinary runtime property write failed at {sourceType}.{propertyName} (declaredType={declaredType}, accessor={property.AccessorType}). " +
+                "This usually indicates a null-sensitive property getter or malformed source data.",
+                ex);
+        }
+    }
+
     #endregion
 
     #region Specialized Array Writers

AyCode.Services/SignalRs/AcBinaryHubProtocol.cs

@@ -964,11 +964,12 @@ public class AcBinaryHubProtocol : IHubProtocol
                 return true;
             }
 
-            // Unknown byte in chunk mode — break out (shouldn't happen).
-            // Note: AsyncPipeReaderInput's WritePos/ReadPos are private, so the previous diagnostic
-            // fields are unavailable here. Enable AsyncPipeReaderInput.DiagnosticLog (DEBUG-only)
-            // for deeper instrumentation when investigating framing-state corruption.
-            _logger?.LogWarning("TryParseChunkData unknown byte {FirstByte} in chunk mode, breaking. " +
+            // Unknown byte in chunk mode.
+            // Real-world case: server-side serialization fails after CHUNK_START was sent, then SignalR
+            // emits a normal framed CloseMessage. The first byte here is then the little-endian payload
+            // length (e.g. 114), not [201]/[202]. If we keep chunk state, subsequent parses keep failing
+            // with the same warning. Instead, tear down chunk mode and re-parse as normal framed message.
+            _logger?.LogWarning("TryParseChunkData unknown byte {FirstByte} in chunk mode, falling back to normal parse. " +
                 "binderHash={BinderHash} inputLength={InputLength} " +
                 "state: streamedArgType={TargetType} deserTaskStatus={TaskStatus} chunkFrameBytesConsumed={ChunkFrameBytesConsumed}",
                 firstByte,
@@ -977,7 +978,10 @@ public class AcBinaryHubProtocol : IHubProtocol
                 state.StreamedArgType.Name,
                 state.DeserTask?.Status.ToString() ?? "null",
                 state.ChunkFrameBytesConsumed);
-            break;
+
+            state.Input.Dispose();
+            _chunkStates.Remove(binder);
+            return TryParseMessage(ref input, binder, out message);
         }
 
         return false;