Fix drag-handoff bugs: gate FX re-resolve on outside-panel, cache unresolvable OS-drag verdict, block double FX-add retry

src/core/ui/drag_out.cpp

@@ -50,8 +50,7 @@ PathList assemblePathList(const std::vector<ResolvedSample>& resolved) {
 
 OsHandoff decideOsHandoff(const std::vector<std::string>& paths) {
     OsHandoff out;
-    out.startOsDrag = !paths.empty();
-    out.releaseInternalDrag = out.startOsDrag;
+    out.handOffToOs = !paths.empty();
     return out;
 }