perf(render): avoid forced FIFO fallback without mailbox

adapters/fparkan-render-vulkan/src/ffi/tests.rs

@@ -418,6 +418,32 @@ fn swapchain_plan_enables_transfer_source_when_surface_supports_it() {
     );
 }
 
+#[test]
+fn swapchain_plan_falls_back_to_immediate_without_overriding_supported_preference() {
+    let mut request = swapchain_request();
+    request.present_modes = vec![
+        vk::PresentModeKHR::IMMEDIATE.as_raw(),
+        vk::PresentModeKHR::FIFO.as_raw(),
+    ];
+    assert_eq!(
+        plan_vulkan_swapchain(&request).unwrap().present_mode,
+        vk::PresentModeKHR::IMMEDIATE.as_raw()
+    );
+    request.preferred_present_mode = vk::PresentModeKHR::FIFO.as_raw();
+    assert_eq!(
+        plan_vulkan_swapchain(&request).unwrap().present_mode,
+        vk::PresentModeKHR::FIFO.as_raw()
+    );
+    request
+        .present_modes
+        .push(vk::PresentModeKHR::MAILBOX.as_raw());
+    request.preferred_present_mode = vk::PresentModeKHR::MAILBOX.as_raw();
+    assert_eq!(
+        plan_vulkan_swapchain(&request).unwrap().present_mode,
+        vk::PresentModeKHR::MAILBOX.as_raw()
+    );
+}
+
 #[test]
 fn swapchain_plan_uses_fifo_and_current_extent_fallbacks() {
     let mut request = swapchain_request();

adapters/fparkan-render-vulkan/src/policy.rs

@@ -495,6 +495,8 @@ fn undefined_surface_format_override(
 fn select_present_mode(present_modes: &[i32], preferred: i32) -> Result<i32, VulkanSwapchainError> {
     if present_modes.contains(&preferred) {
         Ok(preferred)
+    } else if present_modes.contains(&vk::PresentModeKHR::IMMEDIATE.as_raw()) {
+        Ok(vk::PresentModeKHR::IMMEDIATE.as_raw())
     } else if present_modes.contains(&vk::PresentModeKHR::FIFO.as_raw()) {
         Ok(vk::PresentModeKHR::FIFO.as_raw())
     } else {