Batch serial reads before rendering to improve ANSI throughput

Drain all available serial data before calling FlipToScreen so
overlapping screen changes collapse into a single GDI render pass.
Messages are checked between chunks to keep keyboard responsive.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

delphi/TESTMAIN.PAS

@@ -189,18 +189,35 @@ begin
     if FDone then
       Break;
 
-    { Poll serial data -- read one chunk per iteration }
+    { Drain all available serial data before rendering.  Batching     }
+    { many chunks into one render pass avoids per-chunk GDI overhead. }
+    { Messages are checked between chunks so keyboard stays responsive.}
     HasData := False;
     if FComm.PortOpen then
     begin
       S := FComm.Input;
-      if Length(S) > 0 then
+      while (Length(S) > 0) and not FDone do
       begin
         FAnsi.WriteDeferred(S);
         HasData := True;
+        { Check for messages between chunks }
+        while PeekMessage(Msg, 0, 0, 0, pm_Remove or pm_NoYield) do
+        begin
+          if Msg.message = wm_Quit then
+          begin
+            FDone := True;
+            Break;
+          end;
+          TranslateMessage(Msg);
+          DispatchMessage(Msg);
+        end;
+        S := FComm.Input;
       end;
     end;
 
+    if FDone then
+      Break;
+
     { Tick blink (dirties rows if interval elapsed), then render }
     FAnsi.TickBlink;
     FAnsi.FlipToScreen;