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/vst/reasampler_processor.h

@@ -122,6 +122,27 @@ public:
     // resolved selection id ("" if nothing was loaded) for the editor to reflect.
     std::string reloadFromBank();
 
+    // The result of a bank-sync poll (S9/S8): what pollBankSync did this tick, so the editor
+    // can react (repaint / re-snapshot its own view) only when something actually changed.
+    struct BankSyncResult {
+        bool reloaded = false;    // the bank generation changed -> reloadFromBank ran
+        bool applied = false;     // a new assignment request was applied -> selection changed
+    };
+
+    // Poll the S9 bank-generation counter and the S8 assignment request over the bridge, OFF
+    // THE AUDIO THREAD (the editor's UI timer drives this — NEVER process()). Semantics:
+    //   * S9: if the bank generation differs from what we last saw, call reloadFromBank() so a
+    //     recapture/ingest refreshes playback hands-free (atomic swap, glitch-free).
+    //   * S8: if a NEW (generation > last consumed) assignment request names a resolvable
+    //     sample AND this instance is the target (isFocusedTarget), apply it as the selection
+    //     and reload; an unresolvable request is DROPPED silently (marker advanced, no change);
+    //     a non-target instance neither applies nor advances its marker.
+    // The consumed marker advances in component state (marked dirty via the host handler) so a
+    // re-open does not re-apply. `isFocusedTarget` is the shell's thundering-herd policy input
+    // (the editor passes true only for the instance whose editor is open — see the handoff).
+    // Idempotent on an idle tick (generation unchanged + no new request -> no work).
+    BankSyncResult pollBankSync(bool isFocusedTarget);
+
     // The bridge, for the editor's live-state readout + sample list. Owned here; the
     // editor borrows it (outlives the editor).
     ReaperBridge& bridge() { return bridge_; }
@@ -210,6 +231,22 @@ private:
     std::mutex channelModeMutex_;
     ChannelMode channelMode_ = ChannelMode::Mono;
 
+    // The last assignment-request generation this instance CONSUMED (S8 reader). Persisted in
+    // component state (v5) so a re-open does not re-apply a request the user already got and
+    // then changed away from. Written by pollBankSync (UI/timer thread) and getState; read by
+    // pollBankSync + getState; seeded by setState. Guarded against a getState/poll race. NEVER
+    // read on the audio thread. Default 0 -> a genuinely new first assign (gen >= 1) applies.
+    std::mutex assignMarkerMutex_;
+    std::int64_t lastConsumedAssignGeneration_ = 0;
+
+    // The bank generation this instance last SAW (S9 reader). UI/timer-thread only (pollBankSync
+    // is the sole reader/writer) — no mutex needed, and it is NOT persisted. Initialized to a
+    // -1 SENTINEL (no real generation can be negative — parseBankGeneration yields >= 0) so the
+    // FIRST poll after an editor open BASELINES the seen value without a redundant reload (setState
+    // already loaded the current bank); a subsequent generation CHANGE then drives the reload.
+    // NOT read on the audio thread.
+    std::int64_t lastSeenBankGeneration_ = -1;
+
     // Latched from setupProcessing so setActive/reload can size against it. Read
     // off-thread only.
     double sampleRate_ = 44100.0;