Ψ-W1-T4 remediation: gate silent arrange drops, pin surface totality, hedge unverified SDK claims, close comment/exception-safety minors

tests/test_drag_out.cpp

@@ -12,6 +12,7 @@
 
 #include "../src/core/ui/drag_out.h"
 
+#include <cstddef>
 #include <cstdio>
 #include <string>
 #include <vector>
@@ -43,6 +44,14 @@ static const ReaperSurface kAllSurfaces[] = {
     ReaperSurface::FxEmbed,   ReaperSurface::Arrange,    ReaperSurface::Other,
 };
 
+// Pins kAllSurfaces against ReaperSurface::Count so a 7th surface added to the enum without a
+// matching entry here fails the BUILD, not just a silently-incomplete matrix — the compiler
+// alone does not enforce this (no -Wswitch/-Wall or /W4 anywhere in the build; see
+// panel_drag.cpp's onLBtnUp for the same caveat on DropClass).
+static_assert(sizeof(kAllSurfaces) / sizeof(kAllSurfaces[0]) ==
+             static_cast<std::size_t>(ReaperSurface::Count),
+             "kAllSurfaces must list exactly the surfaces below ReaperSurface::Count");
+
 // A point comfortably outside the panel client rect.
 static const int kOutX = 500, kOutY = 150;