fix(input): handle the first Alt+wheel while idle in the wait path

Alt + mouse wheel adjusts the font scale, but it was only handled in the
poll loop that runs after the app wakes. When the app was idle it blocks
in a single timed wait, and that first wheel event went straight to
ImGui, scrolling the window instead of changing the scale until a later
event arrived.

- The Alt+wheel handling is pulled into a shared helper used by both the
  idle wait path and the poll loop, so the first event while idle is
  consumed and triggers a redraw.
- Behaviour is otherwise unchanged: the visual scale updates smoothly and
  the font atlas is rebuilt once scrolling stops.

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

src/main.cpp

@@ -1639,6 +1639,25 @@ int main(int argc, char* argv[])
         else if (isWindowStateEvent(e.type)) settleFrames = kSettleFrames;
     };
 
+    // Deferred font-scale commit: smooth visual update during Alt+scroll,
+    // atlas rebuild after scrolling stops (~200ms idle).
+    Uint64 fontScaleCommitTick = 0;  // 0 = nothing pending
+    // Alt + scroll wheel -> font scale. Returns true if the event was consumed.
+    auto handleAltWheel = [&](const SDL_Event& e) -> bool {
+        if (e.type != SDL_EVENT_MOUSE_WHEEL) return false;
+        if (!(SDL_GetModState() & SDL_KMOD_ALT)) return false;
+        float step = 0.05f * e.wheel.y;
+        float cur  = dragonx::ui::Layout::userFontScale();
+        float next = std::max(1.0f, std::min(1.5f, cur + step));
+        if (next != cur) {
+            // Smooth preview — no atlas rebuild yet
+            dragonx::ui::Layout::setUserFontScaleVisual(next);
+            // Schedule atlas rebuild after scrolling stops
+            fontScaleCommitTick = SDL_GetTicks() + 200;
+        }
+        return true;
+    };
+
     // Headless verification hook (DRAGONX_FULL_SWEEP=1, handled after present), hoisted so the pacing
     // decision can keep its warm-up frames coming.
 #if DRAGONX_ENABLE_UI_SWEEP
@@ -1726,7 +1745,8 @@ int main(int argc, char* argv[])
             SDL_Event waitEvent;
             if (waitMs > 0 && SDL_WaitEventTimeout(&waitEvent, waitMs)) {
                 noteEvent(waitEvent);
-                ImGui_ImplSDL3_ProcessEvent(&waitEvent);
+                if (handleAltWheel(waitEvent)) needsRedraw = true;
+                else ImGui_ImplSDL3_ProcessEvent(&waitEvent);
                 if (waitEvent.type == SDL_EVENT_QUIT) {
                     app.beginShutdown();
                 }
@@ -1828,29 +1848,10 @@ int main(int argc, char* argv[])
 
         // Poll remaining events
         SDL_Event event;
-        // Deferred font-scale commit: smooth visual update during Alt+scroll,
-        // atlas rebuild after scrolling stops (~200ms idle).
-        static Uint64 fontScaleCommitTick = 0;  // 0 = nothing pending
-
         while (SDL_PollEvent(&event)) {
             noteEvent(event);
-            // Alt + scroll wheel: smooth font scale adjustment
+            // Alt + scroll wheel: smooth font scale adjustment (don't pass to ImGui: would scroll windows)
-            if (event.type == SDL_EVENT_MOUSE_WHEEL) {
+            if (handleAltWheel(event)) continue;
-                SDL_Keymod mods = SDL_GetModState();
-                if (mods & SDL_KMOD_ALT) {
-                    float step = 0.05f * event.wheel.y;
-                    float cur  = dragonx::ui::Layout::userFontScale();
-                    float next = std::max(1.0f, std::min(1.5f, cur + step));
-                    if (next != cur) {
-                        // Smooth preview — no atlas rebuild yet
-                        dragonx::ui::Layout::setUserFontScaleVisual(next);
-                        // Schedule atlas rebuild after scrolling stops
-                        fontScaleCommitTick = SDL_GetTicks() + 200;
-                    }
-                    // Don't pass Alt+scroll to ImGui (would scroll windows)
-                    continue;
-                }
-            }
             ImGui_ImplSDL3_ProcessEvent(&event);
             
             if (event.type == SDL_EVENT_QUIT) {