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/capture/bake_land.cpp

@@ -1,7 +1,8 @@
 // bake_land.cpp — see bake_land.h. main.cpp owns the API pointers; this TU gets them
 // extern. REAPER symbols used here (EnumProjects, EnumProjExtState, GetProjExtState,
-// SetProjExtState, ShowConsoleMsg, Undo_BeginBlock2/EndBlock2) are verified against
-// vendor/reaper-sdk/sdk/reaper_plugin_functions.h. Landing one request is bake_landing's.
+// SetProjExtState, ShowConsoleMsg) are verified against
+// vendor/reaper-sdk/sdk/reaper_plugin_functions.h. Landing one request is
+// bake_landing's; the undo block is shell/undo's.
 
 #include "shell/capture/bake_land.h"
 
@@ -19,6 +20,7 @@
 #include "shell/capture/bake_landing.h"
 #include "shell/panel/panel_input.h"     // bankPanelRefresh
 #include "shell/persist/session.h"
+#include "shell/undo/undo_block.h"       // the ONE undo-block opener
 
 #include "reaper_plugin.h"  // UNDO_STATE_MISCCFG
 
@@ -28,8 +30,6 @@
 #define REAPERAPI_WANT_GetProjExtState
 #define REAPERAPI_WANT_SetProjExtState
 #define REAPERAPI_WANT_ShowConsoleMsg
-#define REAPERAPI_WANT_Undo_BeginBlock2
-#define REAPERAPI_WANT_Undo_EndBlock2
 #include "reaper_plugin_functions.h"
 
 namespace reasampler::capture {
@@ -107,26 +107,6 @@ struct ScannedKey {
     wire::BakeKeyOutcome report;
 };
 
-// Undo_BeginBlock2/EndBlock2 as stack RAII, the FxBypassGuard discipline: a landing reads a
-// whole WAV and hashes it, so a bad_alloc between the two calls would otherwise leave an
-// open undo block in the user's project. Closing with an empty description records no undo
-// point, which is what every path that landed nothing wants anyway.
-class UndoBlock {
-public:
-    UndoBlock() { Undo_BeginBlock2(nullptr); }
-    ~UndoBlock() { Undo_EndBlock2(nullptr, description_.c_str(), flags_); }
-    void recordPoint(std::string description, int flags) {
-        description_ = std::move(description);
-        flags_ = flags;
-    }
-    UndoBlock(const UndoBlock&) = delete;
-    UndoBlock& operator=(const UndoBlock&) = delete;
-
-private:
-    std::string description_;
-    int flags_ = 0;
-};
-
 // One entry's write-back, and the proof of whether it took. Guarded whole: it encodes into
 // a fresh string and readKey grows a buffer toward 16 MB, and a throw escaping here would
 // skip the ShowConsoleMsg for EVERY key — the silent console this action exists to make
@@ -206,7 +186,7 @@ void RunResampleBake(ReaSamplerSession& session) {
     // the answers already buffered — the exact no-answer-with-a-silent-console this action
     // exists to make impossible. UndoBlock is inside the try, so unwinding still closes it.
     try {
-        UndoBlock undo;
+        UndoBlock undo(nullptr);
         for (const OpenProject& open : openProjects()) {
             ++tally.tabsScanned;
             const bool activeTab = static_cast<const void*>(open.proj) == active;