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.h

@@ -17,6 +17,7 @@
 // calls live in persist.cpp. It depends on bank_model (pure) for JSON round-trip
 // and capture_paths (pure) for the path arithmetic it drives.
 
+#include <cstdint>
 #include <string>
 
 #include "app_version.h"
@@ -149,6 +150,24 @@ public:
     // reason about the origin build without re-reading ext state.
     const WritingVersion& writingVersion() const { return writingVersion_; }
 
+    // The S9 bank-generation counter (the value stamped under `bank_generation`). Monotonic
+    // per project: recovered on load (so it continues from the stored value rather than
+    // resetting), bumped by bank-content mutations via bumpBankGeneration(), and written on
+    // every saveToActiveProject(). Exposed const for the writer sites to read/log.
+    std::int64_t bankGeneration() const { return bankGeneration_; }
+
+    // Bump the S9 bank-generation counter — call at every bank-CONTENT mutation that changes
+    // what a live instance would PLAY (capture add, re-capture-in-place, sample remove,
+    // move/copy affecting banks, ingest import). NOT the pure-organizational verbs (create /
+    // rename / activate / reorder a bank), which change no existing (bankId, sampleId) ->
+    // content mapping. The bumped value is persisted by the NEXT saveToActiveProject() call
+    // the same mutation already makes (the counter rides the persist blob, so there is no
+    // separate write). In-memory only here — cheap and REAPER-free; the persist is the write.
+    // Over-bumping is safe (a reload that finds unchanged content atomically re-installs the
+    // same instrument, no glitch); under-bumping misses a hands-free refresh, so the sites err
+    // toward bumping. Idempotent per logical op — call once per mutation, before the persist.
+    void bumpBankGeneration() { ++bankGeneration_; }
+
     // Serialize the current book (under the `banks` key), view model, and tail setting
     // to the active project's ext state (namespace "reasampler"), and clear the retired
     // legacy `bank_index` key. Non-destructive beyond writing our own ext-state keys.
@@ -282,6 +301,14 @@ private:
     // the previous project's stamp. Read-only to consumers via writingVersion().
     WritingVersion writingVersion_;
 
+    // The S9 bank-generation counter (peer to writingVersion_). Recovered on EVERY load path
+    // from the stored `bank_generation` stamp (parseBankGeneration; absent -> 0), so it
+    // continues monotonic from the persisted value across reopen and resets cleanly on a
+    // project switch (a different project's counter, not the previous project's). bumped by
+    // bumpBankGeneration() at bank-content mutations and stamped by saveToActiveProject().
+    // Default 0 for an unsaved / never-loaded / pre-S9 session.
+    std::int64_t bankGeneration_ = 0;
+
     // The project identity last observed by poll(), used to detect load/Save-As.
     // The GUID is the PRIMARY signal (a different stored GUID = a different project
     // of record = Load, immune to pointer recycling). The pointer disambiguates the