Draw all of a client's views in one renderer process

The adapter starts one renderer process per client, with the first engine
(again if it has exited), and attaches each engine's channel to it through a
control section (protocol version 5: Control, the -attach event). The renderer
process keeps a window, swap chain and scene per channel on one Direct3D
device, takes the views' frames in turns, and closes a view when its engine
does.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

adapter/renderer_process.hpp

@@ -1,6 +1,7 @@
 #pragma once
-// The renderer process (t5de-renderer.exe, 64-bit) an engine draws through: started with the engine, sent the
-// command stream through a shared memory channel (include/t5de/protocol/channel.hpp), and told to exit with it.
+// The renderer process (t5de-renderer.exe, 64-bit) an engine draws through: one for the whole client, started with
+// the first engine; each engine sends it the command stream through a shared memory channel of its own
+// (include/t5de/protocol/channel.hpp), and closes the channel when it's destroyed.
 
 #include <windows.h>
 
@@ -14,7 +15,8 @@ namespace t5de {
 
 class RendererProcess {
 public:
-    // Starts t5de-renderer.exe from this DLL's folder, drawing into part of window; null if it can't.
+    // A channel to the renderer process (t5de-renderer.exe from this DLL's folder, started if it isn't running),
+    // drawing into part of window; null if it can't.
     static std::unique_ptr<RendererProcess> start(HWND window, protocol::View view);
 
     RendererProcess(const RendererProcess&) = delete;