v0.4: CARemoteLayerServer architecture — crash-safe + GUI inside Ableton window

COMPLETE REWRITE to proper solution:
- Plugin runs in Helper process (crash-safe, like v0.2)
- GUI renders in Helper via CARemoteLayerServer
- PluginBridge.vst3 displays it via CARemoteLayerClient (CALayer inside its own editor)
- Mach port transferred via NSMachBootstrapServer (named port per PID)
- Mouse/keyboard events forwarded from host → helper via Unix socket IPC
- Audio routes via shared memory (same as v0.2)

This gives BOTH crash safety AND GUI inside Ableton's window (including fullscreen).

Based on: Apple's CARemoteLayerServer/Client public API (macOS 10.7+)
Reference: krevis/RemoteLayerDemo on GitHub"

Source/Shared/IPCProtocol.h

@@ -4,11 +4,15 @@
 #include <cstdint>
 
 // IPC Protocol between PluginBridge (parent) and PluginBridgeHelper (child)
-// Transport: Unix domain socket, newline-delimited JSON messages
-// 
-// Flow:
-//   Parent → Helper: commands (load plugin, get/set params, show GUI, quit)
-//   Helper → Parent: responses + notifications (param changes from GUI, crash)
+//
+// v0.4 Architecture:
+// - Audio: POSIX shared memory (zero-copy, same as v0.2)
+// - Sync: Named semaphores (same as v0.2)
+// - Commands: Unix domain socket, newline-delimited JSON
+// - GUI: CARemoteLayerServer in Helper → Mach port → CARemoteLayerClient in Host
+//
+// The Mach port for CARemoteLayerServer is transferred via NSMachBootstrapServer
+// using the name "com.pluginbridge.layer.<parentPid>"
 
 namespace IPC {
 
@@ -18,7 +22,7 @@ inline std::string getSocketPath(int parentPid)
     return "/tmp/pluginbridge_" + std::to_string(parentPid) + ".sock";
 }
 
-// Shared memory name (unique per instance)
+// Shared memory name
 inline std::string getShmName(int parentPid)
 {
     return "pluginbridge_audio_" + std::to_string(parentPid);
@@ -35,64 +39,43 @@ inline std::string getOutputSemName(int parentPid)
     return "pb_output_" + std::to_string(parentPid);
 }
 
-// --- Message Types (Parent → Helper) ---
-
-// Load a plugin by file path
-// {"cmd":"load","path":"/Library/Audio/Plug-Ins/VST3/Pro-Q 4.vst3"}
-// Response: {"ok":true,"name":"Pro-Q 4","params":737} or {"ok":false,"error":"..."}
+// Mach bootstrap port name for CARemoteLayerServer
+inline std::string getLayerPortName(int parentPid)
+{
+    return "com.pluginbridge.layer." + std::to_string(parentPid);
+}
 
-// Unload current plugin
+// --- Message Types (Parent → Helper) ---
+// {"cmd":"load","path":"/path/to/plugin.vst3","sampleRate":44100,"blockSize":512}
 // {"cmd":"unload"}
-// Response: {"ok":true}
-
-// Search parameters by keyword
 // {"cmd":"search_param","keyword":"gain"}
-// Response: {"ok":true,"results":[{"i":12,"n":"Band 1 Gain","v":0.5,"t":"0.0 dB"},...]}
-
-// Get parameter values by index
-// {"cmd":"get_params","ids":[12,13,14]}
-// Response: {"ok":true,"values":{"12":0.5,"13":0.7,"14":0.0}}
-
-// Set parameter values
-// {"cmd":"set_params","values":{"12":0.75,"13":0.3}}
-// Response: {"ok":true}
-
-// Show/hide plugin GUI
+// {"cmd":"get_params","ids":[0,1,2]}
+// {"cmd":"set_params","values":{"0":0.5,"1":0.75}}
 // {"cmd":"show_gui"}
 // {"cmd":"hide_gui"}
-// Response: {"ok":true}
-
-// Get plugin state (for save)
 // {"cmd":"get_state"}
-// Response: {"ok":true,"state":"<base64-encoded state>"}
-
-// Set plugin state (for restore)
-// {"cmd":"set_state","state":"<base64-encoded state>"}
-// Response: {"ok":true}
-
-// Configure audio
+// {"cmd":"set_state","state":"<base64>"}
 // {"cmd":"configure","sampleRate":44100,"blockSize":512,"channels":2}
-// Response: {"ok":true}
-
-// Quit helper
 // {"cmd":"quit"}
-// No response (process exits)
-
-// --- Message Types (Helper → Parent, unsolicited notifications) ---
-
-// Parameter changed from GUI interaction
-// {"notify":"param_changed","index":12,"value":0.75}
-
-// Plugin crashed (sent if helper catches it before dying)
+//
+// --- Mouse/Keyboard forwarding (Parent → Helper) ---
+// {"cmd":"mouse","type":"down","x":120.5,"y":45.0,"button":0}
+// {"cmd":"mouse","type":"up","x":120.5,"y":45.0,"button":0}
+// {"cmd":"mouse","type":"move","x":130.0,"y":50.0}
+// {"cmd":"mouse","type":"drag","x":135.0,"y":52.0,"button":0}
+// {"cmd":"mouse","type":"scroll","x":120.5,"y":45.0,"dx":0,"dy":-3.0}
+// {"cmd":"key","type":"down","keyCode":36,"chars":"a","modifiers":0}
+// {"cmd":"key","type":"up","keyCode":36,"chars":"a","modifiers":0}
+//
+// --- Notifications (Helper → Parent) ---
+// {"notify":"ready","layerPortName":"com.pluginbridge.layer.12345","width":800,"height":600}
+// {"notify":"param_changed","index":5,"value":0.75}
+// {"notify":"resized","width":900,"height":650}
 // {"notify":"crashed","error":"..."}
 
-// Helper ready (sent after startup)
-// {"notify":"ready"}
-
 // --- Constants ---
-
-static constexpr int kMaxMessageSize = 65536;  // 64KB max for state blobs
-static constexpr int kHelperTimeoutMs = 5000;   // 5s to start up
+static constexpr int kMaxMessageSize = 65536;
+static constexpr int kHelperTimeoutMs = 10000;   // 10s for startup (CARemoteLayer init takes time)
 static constexpr int kProcessBlockTimeoutMs = 50; // 50ms max wait in processBlock
 
 } // namespace IPC