first build attempt

src/knob_panel.h

@@ -0,0 +1,32 @@
+/*
+ * MIT License
+ * Author: Mark Allyn
+ *
+ * knob_panel.h — Thread 3 stub: future hardware encoder panel.
+ *
+ * When physical encoders are installed, KnobPanel will read them via
+ * GPIO/serial and write to SharedRenderState under Mutex A.  Until
+ * then, the thread starts but idles immediately without touching
+ * SharedRenderState.  The keyboard equivalents in PPIScope handle
+ * the same state fields in the meantime.
+ */
+
+#pragma once
+#include <thread>
+#include <atomic>
+#include "shared_render_state.h"
+
+class KnobPanel {
+public:
+    explicit KnobPanel(SharedRenderState& srs) : srs_(srs) {}
+
+    void start();
+    void stop();
+
+private:
+    void run();
+
+    SharedRenderState& srs_;
+    std::thread        thread_;
+    std::atomic<bool>  running_{false};
+};