feat(S9/S8): bank-generation change-detection + instrument-side assignment reader

Extension stamps a monotonic bank_generation counter, bumped at content
mutations; the VST3 instrument polls it off-thread on an editor timer and
consumes assignment requests, refreshing playback hands-free.

src/persist.cpp

@@ -96,6 +96,7 @@
 #include "app_version.h"
 #include "capture_paths.h"
 #include "prune_reconcile.h"
+#include "vst/bank_sync.h"  // parseBankGeneration / formatBankGeneration (SHARED with the instrument reader)
 
 #define REAPERAPI_MINIMAL
 #define REAPERAPI_WANT_EnumProjects
@@ -252,6 +253,16 @@ bool ReaSamplerSession::saveToActiveProject() {
     SetProjExtState(static_cast<ReaProject*>(proj), projExtNamespace(),
                     kProjExtVersionKey, stampVersion().c_str());
 
+    // S9: stamp the current bank-generation counter under its own wire-shared key, on the SAME
+    // seam so the counter and MarkProjectDirty stay paired. The value is whatever
+    // bumpBankGeneration() advanced it to since the last save (0 if never bumped / pre-S9), so
+    // every content mutation's own save carries the fresh generation the instrument reads. The
+    // format is the SHARED pure encoder (vst::formatBankGeneration) so writer and reader agree
+    // byte-for-byte — a decimal integer. Additive: does not disturb the blobs above.
+    SetProjExtState(static_cast<ReaProject*>(proj), projExtNamespace(),
+                    kProjExtBankGenKey,
+                    vst::formatBankGeneration(bankGeneration_).c_str());
+
     MarkProjectDirty(static_cast<ReaProject*>(proj));
     return true;
 }
@@ -580,6 +591,16 @@ void ReaSamplerSession::loadFromProject(void* proj, const std::string& projectDi
                                      kProjExtVersionKey)
              : std::string{});
 
+    // S9: recover the bank-generation counter on EVERY load path (peer-symmetry with
+    // writingVersion_/tail_/view_ above), so it continues monotonic from the stored value
+    // rather than resetting to 0 on reopen — a next bump then reads > the stored value. A
+    // project switch reads THAT project's counter, not the previous one's; an absent/malformed
+    // stamp (pre-S9 or corrupt) parses to 0 via the SHARED decoder. proj == nullptr -> 0.
+    bankGeneration_ = vst::parseBankGeneration(
+        proj ? getProjExtStateString(static_cast<ReaProject*>(proj), projExtNamespace(),
+                                     kProjExtBankGenKey)
+             : std::string{});
+
     if (!proj) {
         book_ = BankBook{};
         return;