fix(window): defer caption-button window ops out of the ImGui frame

The custom minimize / maximize / restore buttons are drawn from inside
app.render(), while an ImGui frame is open. Calling SDL to change the
window state there pushes resize events synchronously, which re-enters
the resize watcher and can nest a new frame inside the open one.

- A click now records the requested op instead of acting on it, and the
  window state change is applied once the frame has closed, after the
  pacing block so the follow-up redraw is not dropped.

Windows-only; it rides the borderless caption controls.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main.cpp

@@ -334,6 +334,11 @@ static LRESULT CALLBACK BorderlessWndProc(HWND hwnd, UINT msg,
     return CallWindowProcW(g_sdlWndProc, hwnd, msg, wParam, lParam);
 }
 
+// Caption-button window ops are deferred out of the open ImGui frame and run
+// after the frame closes (SDL pushes resize events synchronously). (C146)
+enum class CaptionOp { None, Minimize, Maximize, Restore };
+static CaptionOp g_pendingCaptionOp = CaptionOp::None;
+
 // Draw custom window-control buttons (minimize / maximize-restore / close)
 // on the foreground draw list, and handle title-bar dragging.
 static void renderBorderlessControls(SDL_Window* window, HWND /*hwnd*/,
@@ -380,7 +385,7 @@ static void renderBorderlessControls(SDL_Window* window, HWND /*hwnd*/,
         float cy = oy + btnH * 0.5f, lx = minX + btnW * 0.5f - iconHalf;
         fg->AddLine(ImVec2(lx, cy), ImVec2(lx + iconHalf * 2.0f, cy),
                     wcIcon, lineThk);
-        if (hov && click) SDL_MinimizeWindow(window);
+        if (hov && click) g_pendingCaptionOp = CaptionOp::Minimize;
     }
 
     // --- Maximize / Restore button ---
@@ -402,10 +407,7 @@ static void renderBorderlessControls(SDL_Window* window, HWND /*hwnd*/,
                         ImVec2(cx + iconHalf, cy + iconHalf - dp),
                         wcIcon, 0, 0, lineThk);
         }
-        if (hov && click) {
-            if (maximized) SDL_RestoreWindow(window);
-            else           SDL_MaximizeWindow(window);
-        }
+        if (hov && click) g_pendingCaptionOp = maximized ? CaptionOp::Restore : CaptionOp::Maximize;
     }
 
     // --- Close button ---
@@ -2374,6 +2376,18 @@ int main(int argc, char* argv[])
                 nextAmbientFrameMs = lastFrameStartNs / 1000000 + interval;
             }
         }
+#ifdef DRAGONX_USE_DX11
+        if (g_pendingCaptionOp != CaptionOp::None) {
+            switch (g_pendingCaptionOp) {
+                case CaptionOp::Minimize: SDL_MinimizeWindow(window); break;
+                case CaptionOp::Maximize: SDL_MaximizeWindow(window); break;
+                case CaptionOp::Restore:  SDL_RestoreWindow(window);  break;
+                default: break;
+            }
+            g_pendingCaptionOp = CaptionOp::None;
+            needsRedraw = true;   // after the pacing block, so it is not overwritten
+        }
+#endif
     }
 
     // Remove resize event watcher