Address review: forwarder split, CreateDelegate guard, API-set docs

- PeHeaderParser: split export forwarders on the FIRST dot (IndexOf), not the
  last. A forwarder is "Module.Function" and the module name has no extension, so
  the last-dot split misparsed export names that themselves contain a dot.
- PeHeaderParser: document that API-set (api-ms-win-*/ext-ms-*) and ordinal
  forwarders are unsupported and should be resolved via the OS loader.
- RemoteFunction.CreateDelegate now throws InvalidOperationException unless the
  session is in-process; an external target's address is not host-mapped and a
  delegate to it would access-violate on invocation. Tests cover both paths.
- Reword the SSE-payload comment: the 16-byte scratch sits below the saved
  return address, which the aligned store leaves intact (it never overwrote it).

Tests: 223 passing, 4 skipped.

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

WhiteMagic/Discovery/PeHeaderParser.cs

@@ -112,6 +112,15 @@ public sealed class PeHeaderParser
     /// <param name="functionName">The exported symbol name (case-sensitive, as stored
     /// in the export name table).</param>
     /// <returns>The absolute address of the export in the target process.</returns>
+    /// <remarks>
+    /// Forwarders are resolved by locating the target module in the process's loaded-module
+    /// list. API-set forwarders (virtual <c>api-ms-win-*</c> / <c>ext-ms-*</c> names) are NOT
+    /// supported: those are not real loaded modules, so resolution through the module list is
+    /// impossible without parsing the API-set schema — such a forwarder throws
+    /// <see cref="NotSupportedException"/>. On modern Windows many system-DLL exports forward
+    /// through API sets; resolve those via the OS loader (<c>GetProcAddress</c>) instead.
+    /// Ordinal forwarders (<c>Module.#N</c>) are likewise unsupported.
+    /// </remarks>
     /// <exception cref="InvalidOperationException">The export is not present.</exception>
     /// <exception cref="NotSupportedException">The export forwards to an ordinal or to a
     /// module (such as an API set) that is not resolvable from the target's module list.</exception>
@@ -212,7 +221,10 @@ public sealed class PeHeaderParser
 
     private IntPtr ResolveForwarder(string forwarder, int depth)
     {
-        int dot = forwarder.LastIndexOf('.');
+        // A forwarder is "Module.Function"; the module name carries no extension, so the
+        // FIRST dot is the boundary. Splitting on the last dot would misparse export names
+        // that themselves contain a dot (e.g. some C++/managed exports).
+        int dot = forwarder.IndexOf('.');
         if (dot <= 0 || dot >= forwarder.Length - 1)
             throw new InvalidDataException($"Malformed export forwarder string '{forwarder}'.");