Fix drag-out losing audio and FX-container drops losing the capture; re-home ingest under shell/actions

src/shell/actions/drag_out_win.cpp

@@ -62,6 +62,29 @@ HGLOBAL buildHDrop(const std::vector<std::string>& paths) {
     return h;
 }
 
+// COM reference counts MUST be interlocked. A CF_HDROP target is free to marshal the data
+// object into another apartment and finish the copy on a background thread AFTER DoDragDrop
+// has returned (Explorer's async file copy does exactly this). A plain ++/-- there races the
+// source thread's post-DoDragDrop Release: one lost increment destroys the object — and with
+// it the source HGLOBAL — before the target reads it, and the drop lands with no file. That
+// race is intermittent and a retry usually wins it; do not "simplify" these back.
+inline ULONG comAddRef(volatile LONG& refs) {
+    return static_cast<ULONG>(InterlockedIncrement(&refs));
+}
+
+// DoDragDrop requires the calling thread to be OLE-initialized — CoInitialize alone is not
+// enough, and an uninitialized thread fails the call outright, so the drag never starts.
+// Relying on REAPER having done it is a first-use hazard: whether it has depends on what else
+// ran first in the session. OleInitialize is per-thread refcounted, so this is additive to
+// whatever the host did; we deliberately never OleUninitialize — the extension lives for the
+// process, and unbalancing a REAPER-owned apartment is the hazard worth avoiding, not this.
+// RPC_E_CHANGED_MODE means the thread joined an MTA, where OLE drag-drop is unavailable.
+bool ensureOleForThisThread() {
+    static thread_local int state = 0;  // 0 untried, 1 ready, -1 unavailable
+    if (state == 0) state = SUCCEEDED(OleInitialize(nullptr)) ? 1 : -1;
+    return state > 0;
+}
+
 // Minimal IDropSource: continue until the (left) button releases or Escape cancels; always
 // request the copy cursor. This is the standard textbook drop source — no custom feedback.
 class DropSource final : public IDropSource {
@@ -76,11 +99,11 @@ public:
         *ppv = nullptr;
         return E_NOINTERFACE;
     }
-    ULONG STDMETHODCALLTYPE AddRef() override { return ++refs_; }
+    ULONG STDMETHODCALLTYPE AddRef() override { return comAddRef(refs_); }
     ULONG STDMETHODCALLTYPE Release() override {
-        const ULONG r = --refs_;
+        const LONG r = InterlockedDecrement(&refs_);
         if (r == 0) delete this;
-        return r;
+        return static_cast<ULONG>(r);
     }
     // IDropSource
     HRESULT STDMETHODCALLTYPE QueryContinueDrag(BOOL escapePressed, DWORD keyState) override {
@@ -92,7 +115,7 @@ public:
         return DRAGDROP_S_USEDEFAULTCURSORS;  // let OLE draw the standard copy cursor
     }
 private:
-    ULONG refs_ = 1;
+    volatile LONG refs_ = 1;
 };
 
 // Minimal IDataObject exposing exactly one format (CF_HDROP / TYMED_HGLOBAL). The HDROP is
@@ -112,11 +135,11 @@ public:
         *ppv = nullptr;
         return E_NOINTERFACE;
     }
-    ULONG STDMETHODCALLTYPE AddRef() override { return ++refs_; }
+    ULONG STDMETHODCALLTYPE AddRef() override { return comAddRef(refs_); }
     ULONG STDMETHODCALLTYPE Release() override {
-        const ULONG r = --refs_;
+        const LONG r = InterlockedDecrement(&refs_);
         if (r == 0) delete this;
-        return r;
+        return static_cast<ULONG>(r);
     }
 
     // IDataObject — the two that matter for a drag source.
@@ -184,7 +207,7 @@ private:
                (fe.tymed & TYMED_HGLOBAL) &&
                fe.dwAspect == DVASPECT_CONTENT;
     }
-    ULONG refs_ = 1;
+    volatile LONG refs_ = 1;
     HGLOBAL hdrop_ = nullptr;
 };
 
@@ -192,10 +215,8 @@ private:
 
 bool initiateDragOut(HWND__* /*panelHwnd*/, const std::vector<std::string>& absolutePaths) {
     if (absolutePaths.empty()) return false;
+    if (!ensureOleForThisThread()) return false;
 
-    // REAPER's main thread is already OLE-initialized (it hosts OLE drag targets); we
-    // deliberately do NOT call OleInitialize — pairing OleUninitialize across a
-    // REAPER-owned apartment is the kind of thing that bites.
     HGLOBAL hdrop = buildHDrop(absolutePaths);
     if (!hdrop) return false;