Fix SWELL drag guard, channel-fork the VST editor window class, dedupe own-module match

Panel drag no longer misfires on SWELL's always-zero wParam; stable/beta VST editors register distinct window classes against their own module instead of colliding on REAPER's; own-module basename matching moves to a tested pure helper.

src/shell/instrument/editor_platform.cpp

@@ -13,6 +13,7 @@
 
 #include "shell/instrument/editor_internal.h"  // (transitively: lice + the kit, Windows only)
 #include "shell/instrument/reasampler_processor.h"
+#include "core/version/app_version.h"  // vstOutputName — channel-forked window class name
 
 using namespace Steinberg;
 
@@ -20,7 +21,32 @@ namespace reasampler::vst {
 
 #ifdef _WIN32
 namespace {
-constexpr const wchar_t* kChildClassName = L"ReaSampler9000VstEditor";
+
+// Channel-forked so stable and beta never fight over one class registration (a second
+// RegisterClassW against an already-taken name silently fails, leaving that channel's editors
+// running the FIRST-registered channel's wndProc). vstOutputName() is ASCII (CMake OUTPUT_NAME),
+// so a plain widen is safe.
+const std::wstring& childClassName() {
+    static const std::wstring name = [] {
+        const std::string& base = version::vstOutputName();
+        return std::wstring(base.begin(), base.end()) + L"VstEditor";
+    }();
+    return name;
+}
+
+// The module holding a given code address — used to resolve THIS wndProc's own module rather
+// than the parent's hInstance REAPER hands us. Registering against the parent would put the class
+// in REAPER's own module, where a second .vst3 (the other channel) sharing that hInstance could
+// collide on the (now channel-forked) name, and any lookup-by-class would resolve into the wrong
+// binary. Takes the address rather than naming wndProc directly so a free function in this
+// anonymous namespace doesn't need access to the private member.
+HMODULE moduleHandleFor(void* codeAddress) {
+    HMODULE mod = nullptr;
+    GetModuleHandleExW(GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS |
+                            GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,
+                        reinterpret_cast<LPCWSTR>(codeAddress), &mod);
+    return mod;
+}
 
 // The change-detection poll (WM_TIMER on the child window). A low-frequency UI-thread
 // timer: responsive enough that a recapture/ingest/assign refreshes within a bounded
@@ -105,8 +131,9 @@ void ReaSamplerEditor::attachedToParent() {
     HWND parent = static_cast<HWND>(systemWindow);
     if (!parent) return;
 
-    HINSTANCE hInst =
-        reinterpret_cast<HINSTANCE>(GetWindowLongPtr(parent, GWLP_HINSTANCE));
+    // Own module, not the parent's hInstance — see moduleHandleFor() above.
+    HINSTANCE hInst = reinterpret_cast<HINSTANCE>(
+        moduleHandleFor(reinterpret_cast<void*>(&ReaSamplerEditor::wndProc)));
     if (!hInst) hInst = GetModuleHandle(nullptr);
 
     static bool classRegistered = false;
@@ -114,7 +141,7 @@ void ReaSamplerEditor::attachedToParent() {
         WNDCLASSW wc{};
         wc.lpfnWndProc = &ReaSamplerEditor::wndProc;
         wc.hInstance = hInst;
-        wc.lpszClassName = kChildClassName;
+        wc.lpszClassName = childClassName().c_str();
         wc.hCursor = LoadCursor(nullptr, IDC_ARROW);
         // CS_DBLCLKS is what makes WM_LBUTTONDBLCLK arrive at all. It also REPLACES the second
         // WM_LBUTTONDOWN of a double-click, so every surface that counted two downs (Browse's
@@ -134,7 +161,7 @@ void ReaSamplerEditor::attachedToParent() {
     refreshFromBank();
 
     const ViewRect& r = getRect();
-    childHwnd_ = CreateWindowExW(0, kChildClassName, L"", WS_CHILD | WS_VISIBLE, 0, 0,
+    childHwnd_ = CreateWindowExW(0, childClassName().c_str(), L"", WS_CHILD | WS_VISIBLE, 0, 0,
                                  r.getWidth(), r.getHeight(), parent, nullptr, hInst, nullptr);
     if (childHwnd_) {
         SetWindowLongPtr(childHwnd_, GWLP_USERDATA, reinterpret_cast<LONG_PTR>(this));