Add memory-region query, enumeration, and scoped protection

Implements VirtualQueryEx + MEMORY_BASIC_INFORMATION wrappers, the immutable MemoryRegion record, the ProtectionScope disposable helper, and MemoryBase.QueryRegion/EnumerateRegions/ChangeProtection. Closes section 1 of add-thread-region-finder.

WhiteMagic/MemoryBase.cs

@@ -1,5 +1,7 @@
 using WhiteMagic.Hooking;
+using WhiteMagic.Memory;
 using WhiteMagic.Native;
+using System.Collections.Generic;
 using System.Runtime.InteropServices;
 using System.Text;
 
@@ -268,6 +270,58 @@ public abstract class MemoryBase : IDisposable
         return (IntPtr)((nint)absolute - (nint)ImageBase);
     }
 
+    // ── Memory region query ────────────────────────────────────────────────
+
+    /// <summary>
+    /// Queries the memory region that contains <paramref name="address"/> in the target
+    /// process using <c>VirtualQueryEx</c>.
+    /// </summary>
+    /// <returns>An immutable snapshot of the region.</returns>
+    /// <exception cref="InvalidOperationException">The query fails.</exception>
+    public MemoryRegion QueryRegion(IntPtr address)
+    {
+        nuint bufferSize = (nuint)Marshal.SizeOf<MemoryBasicInformation>();
+        nuint result = NativeMethods.VirtualQueryEx(Handle, address, out MemoryBasicInformation info, bufferSize);
+
+        if (result == 0)
+        {
+            int error = Marshal.GetLastPInvokeError();
+            throw new InvalidOperationException($"VirtualQueryEx failed for address 0x{address:X}: error {error}.");
+        }
+
+        return new MemoryRegion(info);
+    }
+
+    /// <summary>
+    /// Enumerates the memory regions of the target process from the lowest address upward.
+    /// The walk is lazy; callers can stop early without walking the entire address space.
+    /// </summary>
+    public IEnumerable<MemoryRegion> EnumerateRegions()
+    {
+        IntPtr address = IntPtr.Zero;
+        nuint bufferSize = (nuint)Marshal.SizeOf<MemoryBasicInformation>();
+
+        while (true)
+        {
+            nuint result = NativeMethods.VirtualQueryEx(Handle, address, out MemoryBasicInformation info, bufferSize);
+            if (result == 0)
+                yield break;
+
+            yield return new MemoryRegion(info);
+            address = info.BaseAddress + (nint)info.RegionSize;
+        }
+    }
+
+    /// <summary>
+    /// Changes the page protection on a region of memory and returns a disposable scope
+    /// that restores the original protection on dispose, including when an exception escapes
+    /// the guarded body.
+    /// </summary>
+    public ProtectionScope ChangeProtection(IntPtr address, nint size, MemoryProtectionType protection)
+    {
+        return new ProtectionScope(this, address, size, protection);
+    }
+
     // ── Lifecycle ──────────────────────────────────────────────────────────
 
     /// <inheritdoc />