Fix thread namespace collision and tighten executable stub allocation

Fully qualifies System.Threading.Thread in DllInjector after introducing the WhiteMagic.Thread namespace, and replaces the broken+too-small near-allocation loop with a symmetric +/-2 GiB search so the x64 call stub always lands within rel32 range.

WhiteMagic/Execution/RemoteThreadExecutor.cs

@@ -472,27 +472,22 @@ public sealed class RemoteThreadExecutor
         nuint mask = AllocationGranularity - (nuint)1;
         nuint aligned = (preferred + AllocationGranularity - (nuint)1) & ~mask;
 
-        for (int i = 0; i < NearAllocationAttempts; i++)
+        for (long delta = 0; delta <= (long)0x7FFF; delta++)
         {
-            nuint candidate;
-            if (i == 0)
-            {
-                candidate = aligned;
-            }
-            else if ((i & 1) == 1)
-            {
-                candidate = aligned + (nuint)i * AllocationGranularity;
-            }
-            else
-            {
-                nuint offset = (nuint)i * AllocationGranularity;
-                if (offset > aligned)
-                {
-                    continue;
-                }
+            long signedOffset = delta * (long)AllocationGranularity;
 
-                candidate = aligned - offset;
-            }
+            // Try above, then below the target. Keep the original address as the first attempt.
+            for (int sign = 0; sign < 2; sign++)
+            {
+                if (delta == 0 && sign != 0)
+                    continue;
+
+                long offset = sign == 0 ? signedOffset : -signedOffset;
+                nuint candidate = (nuint)((long)aligned + offset);
+
+                // Avoid underflow to zero on below-target search.
+                if (offset < 0 && candidate >= aligned)
+                    continue;
 
                 IntPtr result = NativeMethods.VirtualAllocEx(
                     handle,
@@ -503,15 +498,16 @@ public sealed class RemoteThreadExecutor
 
                 if (result != IntPtr.Zero)
                 {
+                    long distance = (long)(nuint)(nint)result - (long)(nuint)(nint)preferredAddress;
+                    if (distance >= int.MinValue && distance <= int.MaxValue)
                         return result;
+
+                    // The allocator gave us a nearby candidate but on the wrong side
+                    // of the 2 GiB boundary; treat it as unusable and keep searching.
+                    NativeMethods.VirtualFreeEx(handle, result, 0, MemoryFreeType.Release);
+                }
             }
         }
 
-        return NativeMethods.VirtualAllocEx(
-            handle,
-            IntPtr.Zero,
-            size,
-            MemoryAllocationType.Commit | MemoryAllocationType.Reserve,
-            MemoryProtectionType.ExecuteReadWrite);
-    }
+        return IntPtr.Zero;    }
 }

WhiteMagic/Injection/DllInjector.cs

@@ -383,7 +383,7 @@ public sealed class DllInjector
             if (value != IntPtr.Zero)
                 return value;
 
-            Thread.Sleep(5);
+            System.Threading.Thread.Sleep(5);
         }
 
         return IntPtr.Zero;

WhiteMagicTest/Injection/DllInjectorTests.cs

@@ -1,4 +1,5 @@
 using System.Runtime.InteropServices;
+using Thread = System.Threading.Thread;
 using WhiteMagic;
 using WhiteMagic.Injection;
 using WhiteMagic.Native;
@@ -69,7 +70,7 @@ public class DllInjectorTests
         int osThreadId = 0;
         Exception? threadError = null;
 
-        var helper = new Thread(() =>
+        var helper = new System.Threading.Thread(() =>
         {
             try
             {
@@ -80,7 +81,7 @@ public class DllInjectorTests
                 // also be stopped once its original context is restored.
                 while (!stopEvent.IsSet)
                 {
-                    Thread.Sleep(10);
+                    System.Threading.Thread.Sleep(10);
                 }
             }
             catch (Exception ex)