Fix IcedAssembler immediate overflow and unwrap invoke exceptions

- TryBind wraps Convert.ChangeType in TryChangeType so an immediate that
  overflows a candidate parameter type returns false (letting a wider overload
  be tried) instead of throwing OverflowException out of assembly. Verified:
  "mov eax, 4294967295" and "mov eax, -2147483649" no longer crash.
- Immediate now carries a boxed long OR ulong; TryParseImmediate parses decimal
  values above long.MaxValue via a ulong fallback, and hex via ulong. Previously
  such literals were rejected at parse time.
- Unwrap TargetInvocationException from method.Invoke so callers see the real
  Iced failure, not the reflection wrapper.

Tests: 231 passing, 4 skipped.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

WhiteMagic/Assembly/IcedAssembler.cs

@@ -128,8 +128,17 @@ public sealed class IcedAssembler : IAssembler
                 continue;
 
             if (TryBind(parameters, operands, out object?[]? boundArgs))
+            {
+                try
                 {
                     method.Invoke(assembler, boundArgs);
+                }
+                catch (TargetInvocationException ex) when (ex.InnerException is not null)
+                {
+                    // Surface the real Iced failure rather than the reflection wrapper.
+                    throw ex.InnerException;
+                }
+
                 return;
             }
         }
@@ -151,7 +160,16 @@ public sealed class IcedAssembler : IAssembler
             switch (operand)
             {
                 case Immediate imm when IsNumeric(paramType):
-                    args[i] = Convert.ChangeType(imm.Value, paramType, CultureInfo.InvariantCulture);
+                    // An immediate that overflows this parameter's type means this overload
+                    // is the wrong width; return false so a wider overload can be tried
+                    // instead of crashing the whole assembly.
+                    if (!TryChangeType(imm.Value, paramType, out object? converted))
+                    {
+                        boundArgs = null;
+                        return false;
+                    }
+
+                    args[i] = converted;
                     break;
 
                 case not null when paramType.IsInstanceOfType(operand):
@@ -178,28 +196,63 @@ public sealed class IcedAssembler : IAssembler
         if (labels.TryGetValue(token, out Label label))
             return label;
 
-        if (TryParseImmediate(token, out long value))
-            return new Immediate(value);
+        if (TryParseImmediate(token, out object? value))
+            return new Immediate(value!);
 
         throw new NotSupportedException(
             $"Unrecognized operand '{token}' (expected a register, an immediate, or a label).");
     }
 
-    private static bool TryParseImmediate(string token, out long value)
+    // Parses an immediate as the narrowest of long/ulong that holds it, boxed. Storing the
+    // widest representation lets TryChangeType later narrow it to whatever integer parameter
+    // the chosen overload expects — and reject (rather than crash on) values that do not fit.
+    private static bool TryParseImmediate(string token, out object? value)
     {
+        value = null;
         bool negative = token.StartsWith('-');
         string body = negative ? token[1..] : token;
 
-        bool ok;
         if (body.StartsWith("0x", StringComparison.OrdinalIgnoreCase))
-            ok = long.TryParse(body[2..], NumberStyles.HexNumber, CultureInfo.InvariantCulture, out value);
+        {
+            if (!ulong.TryParse(body[2..], NumberStyles.HexNumber, CultureInfo.InvariantCulture, out ulong hex))
+                return false;
+
+            value = negative ? -(long)hex : hex;
+            return true;
+        }
+
+        if (negative)
+        {
+            if (!long.TryParse(token, NumberStyles.Integer, CultureInfo.InvariantCulture, out long signed))
+                return false;
+
+            value = signed;
+            return true;
+        }
+
+        // Non-negative decimal: prefer long, fall back to ulong for values above long.MaxValue.
+        if (long.TryParse(body, NumberStyles.Integer, CultureInfo.InvariantCulture, out long asLong))
+            value = asLong;
+        else if (ulong.TryParse(body, NumberStyles.Integer, CultureInfo.InvariantCulture, out ulong asULong))
+            value = asULong;
         else
-            ok = long.TryParse(body, NumberStyles.Integer, CultureInfo.InvariantCulture, out value);
+            return false;
 
-        if (ok && negative)
-            value = -value;
+        return true;
+    }
 
-        return ok;
+    private static bool TryChangeType(object value, Type targetType, out object? result)
+    {
+        try
+        {
+            result = Convert.ChangeType(value, targetType, CultureInfo.InvariantCulture);
+            return true;
+        }
+        catch (Exception ex) when (ex is OverflowException or InvalidCastException or FormatException)
+        {
+            result = null;
+            return false;
+        }
     }
 
     private static bool IsNumeric(Type type) => Type.GetTypeCode(type) is
@@ -266,9 +319,10 @@ public sealed class IcedAssembler : IAssembler
         return map;
     }
 
-    // A parsed immediate, distinguished from register/label operands so binding can widen
-    // or narrow it to whichever integer parameter type the chosen overload expects.
-    private readonly record struct Immediate(long Value);
+    // A parsed immediate (boxed long or ulong), distinguished from register/label operands
+    // so binding can narrow it to whichever integer parameter type the chosen overload
+    // expects — or reject it when it does not fit.
+    private readonly record struct Immediate(object Value);
 
     private sealed class ByteListCodeWriter : CodeWriter
     {

WhiteMagicTest/Assembly/IcedAssemblerTests.cs

@@ -82,6 +82,32 @@ public class IcedAssemblerTests
         Assert.Equal(expected, jmp.NearBranchTarget);
     }
 
+    [Theory]
+    [InlineData("mov eax, 4294967295")]   // 0xFFFFFFFF — needs the uint overload, not int
+    [InlineData("mov eax, 0xFFFFFFFF")]    // same value, hex form
+    [InlineData("mov rax, 18446744073709551615")] // ulong.MaxValue — decimal above long.MaxValue
+    public void Assemble_binds_wide_unsigned_immediates(string source)
+    {
+        var assembler = new IcedAssembler(64);
+
+        byte[] code = assembler.Assemble(source);
+        Assert.NotEmpty(code);
+
+        Instruction[] instructions = Disassemble(code, 64, 0);
+        Assert.Single(instructions);
+        Assert.Equal(Mnemonic.Mov, instructions[0].Mnemonic);
+    }
+
+    [Fact]
+    public void Assemble_rejects_immediate_that_fits_no_overload_without_crashing()
+    {
+        var assembler = new IcedAssembler(64);
+
+        // -2147483649 is below int.MinValue and eax has no wider signed overload; must be a
+        // clean NotSupportedException, not an OverflowException escaping from ChangeType.
+        Assert.Throws<NotSupportedException>(() => assembler.Assemble("mov eax, -2147483649"));
+    }
+
     [Fact]
     public void Assemble_throws_on_unsupported_operand()
     {