One undo-block opener for the whole tree: fourteen sites route through it, and the reclaim span can no longer swallow a user's act

The drain refuses a tick inside a foreign block; applyMode wakes the reclaimer
before it opens the span.

src/shell/actions/instrument_drop_win.cpp

@@ -13,6 +13,7 @@
 
 #include "core/version/app_version.h"      // vstPluginName() — the CHANNEL-correct FX name (stable/beta pairing)
 #include "core/wire/instrument_drop.h"  // classifyReaperSurface — the PURE, unit-tested classifier
+#include "shell/undo/undo_block.h"      // the ONE undo-block opener
 
 #include "reaper_plugin.h"
 
@@ -22,8 +23,6 @@
 #define REAPERAPI_WANT_TrackFX_Delete
 #define REAPERAPI_WANT_TrackFX_GetCount
 #define REAPERAPI_WANT_TrackFX_SetPreset
-#define REAPERAPI_WANT_Undo_BeginBlock2
-#define REAPERAPI_WANT_Undo_EndBlock2
 #include "reaper_plugin_functions.h"
 
 namespace reasampler {
@@ -138,9 +137,9 @@ bool loadInstrumentOntoTrack(MediaTrack* track, const std::vector<std::uint8_t>&
 bool performInstrumentDrop(MediaTrack* track, const std::vector<std::uint8_t>& presetBytes) {
     if (!track || presetBytes.empty()) return false;
 
-    Undo_BeginBlock2(nullptr);
+    UndoBlock undo(nullptr);
     const bool ok = loadInstrumentOntoTrack(track, presetBytes);
-    Undo_EndBlock2(nullptr, "ReaSampler: drop capture onto FX chain", -1);
+    undo.recordPoint("ReaSampler: drop capture onto FX chain", -1);
     return ok;
 }