fix #387: window resize never recreated the Vulkan swapchain (stretch)

User report: resolution picks (and window drags) stretched the image
instead of changing the pixel count. Root cause: Campaign V slice V11
deleted the GL viewport target and left a null target, assuming the
driver's OUT_OF_DATE/SUBOPTIMAL acquire/present results would drive
swapchain recreation on resize. That is driver-dependent and
spec-insufficient — this machine's Windows AMD driver keeps presenting
the stale-extent swapchain scaled to the new window indefinitely, so
OnFramebufferResize only ever updated the camera aspect while every
pass (UI included) kept rendering at the old extent.

Fix: SwapchainRecreateViewportTarget implements the existing
IFramebufferViewportTarget seam for Vulkan and arms
VulkanGraphicsContext.RequestRecreate() on every resize event; the next
PrepareFrame rebuilds the swapchain at the live FramebufferSize (bursts
collapse to one recreation, stale events cannot install a stale extent,
minimised sizes stay gated by FramebufferResizeController).

Tests: SwapchainRecreateViewportTargetTests (target contract, size-
agnostic arming, null hook, controller-to-target end-to-end with the
minimised gate). Full Debug App suite 4,941/3 skips.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/AcDream.App.Tests/Composition/SwapchainRecreateViewportTargetTests.cs

@@ -0,0 +1,80 @@
+using AcDream.App.Composition;
+using AcDream.App.Input;
+using AcDream.App.Rendering;
+
+namespace AcDream.App.Tests.Composition;
+
+/// <summary>
+/// #387: the V11 null viewport target assumed the driver's OUT_OF_DATE/
+/// SUBOPTIMAL results would drive swapchain recreation on window resize; on
+/// Windows AMD the driver instead presents the stale-extent swapchain scaled
+/// to the new window (the "resolution pick just stretches" 2026-08-13 user
+/// gate report). These pin the replacement target's contract: every resize
+/// event reaching the seam arms the context's frame-boundary recreation.
+/// </summary>
+public sealed class SwapchainRecreateViewportTargetTests
+{
+    [Fact]
+    public void ResizeViewport_ArmsRecreation_OncePerEvent()
+    {
+        int armed = 0;
+        IFramebufferViewportTarget target =
+            new VulkanHostInputCameraCompositionFactory.SwapchainRecreateViewportTarget(
+                () => armed++);
+
+        target.ResizeViewport(1024, 768);
+        Assert.Equal(1, armed);
+
+        // A second resize arms again — the context collapses bursts itself at
+        // the frame boundary (it re-reads the live FramebufferSize), so the
+        // target must never de-duplicate or latch.
+        target.ResizeViewport(800, 600);
+        Assert.Equal(2, armed);
+    }
+
+    [Fact]
+    public void ResizeViewport_IgnoresTheEventSize_ContextReadsLiveFramebuffer()
+    {
+        // The width/height are deliberately unused (doc on the target): the
+        // context reads the CURRENT framebuffer size at the frame boundary,
+        // so a stale event cannot install a stale extent. Pin that the arm
+        // fires regardless of the reported size values.
+        int armed = 0;
+        IFramebufferViewportTarget target =
+            new VulkanHostInputCameraCompositionFactory.SwapchainRecreateViewportTarget(
+                () => armed++);
+
+        target.ResizeViewport(int.MaxValue, 1);
+        Assert.Equal(1, armed);
+    }
+
+    [Fact]
+    public void Constructor_RejectsNullRecreateHook()
+    {
+        Assert.Throws<ArgumentNullException>(() =>
+            new VulkanHostInputCameraCompositionFactory.SwapchainRecreateViewportTarget(null!));
+    }
+
+    [Fact]
+    public void ResizeController_DeliversResizeEventsToTheBoundTarget()
+    {
+        // The end-to-end seam FramebufferResizeController.Resize →
+        // ResizeViewport → arm: the same event flow GameWindow's
+        // OnFramebufferResize drives in production. Zero-area (minimised)
+        // events are gated by the controller and must NOT arm.
+        int armed = 0;
+        var controller = new FramebufferResizeController(new ViewportAspectState());
+        controller.BindViewport(
+            new VulkanHostInputCameraCompositionFactory.SwapchainRecreateViewportTarget(
+                () => armed++));
+
+        controller.Resize(1280, 720);
+        Assert.Equal(1, armed);
+
+        controller.Resize(0, 0);       // minimised — gated, no arm
+        Assert.Equal(1, armed);
+
+        controller.Resize(1024, 768);
+        Assert.Equal(2, armed);
+    }
+}