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_editor.cpp

@@ -38,6 +38,14 @@ namespace {
 #ifdef _WIN32
 constexpr const wchar_t* kChildClassName = L"ReaSampler9000VstEditor";
 
+// The S9/S8 change-detection poll (WM_TIMER on the child window). A low-frequency UI-thread
+// timer: responsive enough that a recapture/ingest/assign refreshes "within a bounded cadence"
+// (the S9 verify criterion) yet cheap — three small ext-state reads per tick, coalescing many
+// bumps between ticks into one reload. 500 ms is a deliberate build-time residual: fast enough
+// to feel hands-free, slow enough to be free. The id is a per-window SetTimer id (any nonzero).
+constexpr UINT_PTR kSyncTimerId = 1;
+constexpr UINT     kSyncTimerIntervalMs = 500;
+
 // Top-level band metrics (shell arithmetic — the load-bearing card/tab/key/zone geometry
 // is in capture_browser / keyboard_strip). The title band names the plugin + a live
 // readout; the toggle band carries the Browser/Zones switch; the setup band (single-
@@ -173,6 +181,35 @@ void ReaSamplerEditor::rebuildVisible() {
     }
 }
 
+#ifdef _WIN32
+// Windows-only (the WM_TIMER cadence + invalidate() are the Win32 child-window path). Declared
+// under the same _WIN32 guard in the header; keep the definition guarded to match (D5 makes
+// Windows the only build target, but the TU must still compile elsewhere).
+void ReaSamplerEditor::onSyncTimer() {
+    // UI thread (WM_TIMER). Poll the S9 bank generation + the S8 assignment request via the
+    // processor (off the audio thread — the poll itself never touches process()). NEVER while a
+    // drag is in flight: a reload mid-drag would rebuild the instrument and repaint under the
+    // user's cursor, yanking the edit. The next tick (500 ms) picks up the change after release.
+    if (!processor_) return;
+    if (drag_ != DragKind::kNone) return;  // defer past the in-flight edit
+
+    // An open editor marks THIS instance the focused assignment target (the thundering-herd
+    // policy — only an editor-open instance applies a pending assign; see the handoff). Pass
+    // true so this instance consumes the request; instances with no editor open do not poll at
+    // all (the timer is bound to the child window), so they never contend for the request.
+    const ReaSamplerProcessor::BankSyncResult r = processor_->pollBankSync(/*isFocusedTarget=*/true);
+
+    // Re-snapshot the editor's own view only when something changed (a reload from a bank
+    // content change, or an applied assignment). refreshFromBank re-reads the bank blob + the
+    // processor's (possibly just-updated) selection/map and drops the stale thumbnail/PCM
+    // caches, then repaints — so the browser + setup surface reflect the new bank hands-free.
+    if (r.reloaded || r.applied) {
+        refreshFromBank();
+        invalidate();
+    }
+}
+#endif  // _WIN32
+
 void ReaSamplerEditor::commitAndReload() {
     // UI thread only. Publish the edited selection + zones to the processor, then rebuild
     // the instrument off the audio thread (reloadFromBank bakes them into the live Keymap).
@@ -372,11 +409,21 @@ void ReaSamplerEditor::attachedToParent() {
                                  r.getWidth(), r.getHeight(), parent, nullptr, hInst, nullptr);
     if (childHwnd_) {
         SetWindowLongPtr(childHwnd_, GWLP_USERDATA, reinterpret_cast<LONG_PTR>(this));
+        // Start the S9/S8 change-detection poll (UI thread). Tied to the child window's
+        // lifetime — created here, killed in removedFromParent — so an instance whose editor
+        // is closed does NOT poll (the editor-open-only cadence; see the handoff limitation).
+        SetTimer(childHwnd_, kSyncTimerId, kSyncTimerIntervalMs, nullptr);
+        // Poll ONCE immediately so a pending assignment (an S8 ingest fired while this editor
+        // was closed) or a bank change applies the instant the editor opens, rather than waiting
+        // up to one timer interval. refreshFromBank above already primed the view; this folds in
+        // any pending assign/generation so the just-opened editor shows the assigned capture.
+        onSyncTimer();
     }
 }
 
 void ReaSamplerEditor::removedFromParent() {
     if (childHwnd_) {
+        KillTimer(childHwnd_, kSyncTimerId);  // stop the poll before the window goes away
         DestroyWindow(childHwnd_);
         childHwnd_ = nullptr;
     }
@@ -1063,6 +1110,9 @@ LRESULT CALLBACK ReaSamplerEditor::wndProc(HWND hwnd, UINT msg, WPARAM wParam,
                 self->invalidate();
             }
             return 0;
+        case WM_TIMER:
+            if (self && wParam == kSyncTimerId) self->onSyncTimer();
+            return 0;
         case WM_ERASEBKGND:
             return 1;  // fully repaint in WM_PAINT; skip the flicker-inducing erase
         default: