[Fix] (MG_Backend/DirectVulkan): keep the transient arena's outgrown buffers alive until frame rewind - the transient drain freed them while frame-serial memos still bound them

MobileGL/MG_Backend/DirectVulkan/Renderer/BufferArena.cpp

@@ -111,6 +111,11 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         }
 
         if (buffer.IsValid()) {
+            // Outgrown, not dead: every BufferSlice handed out from this frame's arena so far
+            // still names it, and those slices stay in service until the frame slot is rewound
+            // (VkBufferResource::transientSlice, the converted-vertex-stream cache, the draw
+            // memos). The release therefore has to survive every mid-frame reclaim and land on
+            // the next ResetFrame of this slot - see VkBufferManager::CollectAllDeferredReleases.
             m_deferredReleases[frameIndex].push_back(std::move(buffer));
         }
 

MobileGL/MG_Backend/DirectVulkan/Renderer/VkBufferManager.cpp

@@ -161,12 +161,23 @@ namespace MobileGL::MG_Backend::DirectVulkan {
     }
 
     void VkBufferManager::CollectAllDeferredReleases() {
+        // Per-resource releases only. Every one of them was deferred behind a BumpSliceEpoch,
+        // so no memo can still name the handle, and the caller has proved the GPU is idle.
+        //
+        // The transient arena's releases are deliberately NOT collected here. A buffer lands
+        // there when the arena outgrows it mid-frame (BufferArena::EnsureCapacity), and at
+        // that moment every slice already handed out from this frame's arena still names it -
+        // VkBufferResource::transientSlice above all, which AcquireStreamedSlice keeps
+        // serving for the whole frame serial on the strength of transientFrameSerial alone.
+        // Nothing bumps the slice epoch for those other resources, so freeing the buffer
+        // here left the streamed memo handing a destroyed VkBuffer to vkCmdBindIndexBuffer
+        // (llvmpipe then faulted inside the draw; the Create/Flywheel indirect retrace died
+        // exactly this way). Mid-frame drains do not advance m_frameSerial, so they must not
+        // free arena storage either: the arena's own ResetFrame/BeginFrame is the point where
+        // the slot's slices stop being reachable, and that is where these releases land.
         for (Uint32 frameIndex = 0; frameIndex < m_deferredBufferReleases.size(); ++frameIndex) {
             CollectDeferredReleases(frameIndex);
         }
-        for (Uint32 frameIndex = 0; frameIndex < m_transientUploadArena.GetFrameCount(); ++frameIndex) {
-            m_transientUploadArena.CollectDeferredReleases(frameIndex);
-        }
     }
 
     void VkBufferManager::NotifyDeviceIdle() {

MobileGL/MG_Backend/DirectVulkan/Renderer/VkBufferManager.h

@@ -102,10 +102,11 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         // Recreate all per-frame transient arenas
         Bool RecreateTransientArenas(Uint32 frameCount);
         void BeginFrame(Uint32 frameIndex);
-        // Drains every frame slot's deferred buffer/resource releases (and the
-        // transient arena's parked superseded blocks). Only valid when the
-        // caller has proven every queue submission complete; used by the
-        // present-less frame-boundary drain.
+        // Drains every frame slot's deferred buffer/resource releases. Only valid when
+        // the caller has proven every queue submission complete; used by the present-less
+        // frame-boundary drain. Deliberately does NOT touch the transient arena's parked
+        // superseded blocks: those are still named by this frame's slices (see the
+        // definition), and only a frame rewind retires them.
         void CollectAllDeferredReleases();
         // All previously submitted GPU work has completed (vkDeviceWaitIdle).
         void NotifyDeviceIdle();