[Refactor] (P13 W5 S3): the apply side's backend comes through MG_Backend's ApplyRoleBackend hook, which ServerLoop installs.

MobileGL/MG_Backend/DirectVulkan/Renderer/VertexInputStateFactory.cpp

@@ -6,6 +6,7 @@
 // SPDX-License-Identifier: LGPL-3.0-only
 // End of Source File Header
 
+#include <MG_Backend/Record/ApplyRoleBackend.h>
 #include "VertexInputStateFactory.h"
 #include "MagmaPipeArms.h"
 #include "MG_Util/Converters/MGToStr/DataTypeConverter.h"
@@ -464,7 +465,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
                                                attr.IsBgra, attr.IsLong);
             auto conversion = VertexStreamConversion::None;
             if (format == VK_FORMAT_UNDEFINED && type == DataType::Float64) {
-                const auto* backend = MG_Remote::Server::ServerLoopInstance().Backend();
+                const auto* backend = MG_Backend::ApplyRoleBackend();
                 if (backend && backend->GetDynamicParameters().SupportsFloat64VertexAttributes) {
                     // Exactly the monolith arm's answer for the same state: with native fp64
                     // the module KEPT its 64-bit inputs (DemoteFloat64Pass did not run), so

MobileGL/MG_Backend/Record/ApplyRoleBackend.h

@@ -0,0 +1,27 @@
+// MobileGL - MobileGL/MG_Backend/Record/ApplyRoleBackend.h
+// Copyright (c) 2025-2026 MobileGL-Dev
+// Licensed under the GNU Lesser General Public License v3.0:
+//   https://www.gnu.org/licenses/gpl-3.0.txt
+//   https://www.gnu.org/licenses/lgpl-3.0.txt
+// SPDX-License-Identifier: LGPL-3.0-only
+// End of Source File Header
+
+// P13 W5: WHOSE BACKEND ANSWERS A CAPABILITY QUESTION ON THE APPLY SIDE. Under a transport the
+// server's own backend (ServerLoop's) is the authority for the records it applies; the record arm
+// asked MG_Remote for it by name, which a library without MG_Remote cannot. The answer now comes
+// through this hook, which ServerLoop.cpp installs at static init. Without it - a library without
+// a transport - the answer is null, which is exactly what a monolith process got before (a
+// monolith has no server loop, so its server backend was always null).
+
+#pragma once
+
+namespace MobileGL::MG_Backend {
+    class BackendObject;
+
+    using ApplyRoleBackendHook = BackendObject* (*)();
+    inline constinit ApplyRoleBackendHook gApplyRoleBackendHook = nullptr;
+
+    inline BackendObject* ApplyRoleBackend() {
+        return gApplyRoleBackendHook != nullptr ? gApplyRoleBackendHook() : nullptr;
+    }
+} // namespace MobileGL::MG_Backend

MobileGL/MG_Remote/Server/ServerLoop.cpp

@@ -9,6 +9,7 @@
 // P5 package v1: the apply thread, its affinity, its parking, and the EGL ownership move.
 
 #include "ServerLoop.h"
+#include <MG_Backend/Record/ApplyRoleBackend.h>
 #include "ApplyThreadPolicy.h"
 #include "SessionRuntime.h"
 #include <MG_Remote/FatalFunnel.h>
@@ -1460,6 +1461,18 @@ namespace MobileGL::MG_Remote::Server {
         return instance;
     }
 
+    // P13 W5: the record arm asks for the apply side's backend through MG_Backend's hook
+    // (Record/ApplyRoleBackend.h), which has no MG_Remote to name. Installed at static init so it
+    // answers from the first record on, exactly as the direct ServerLoopInstance().Backend() did.
+    namespace {
+        [[maybe_unused]] const bool g_applyRoleBackendHookInstalled = [] {
+            MG_Backend::gApplyRoleBackendHook = []() -> MG_Backend::BackendObject* {
+                return ServerLoopInstance().Backend();
+            };
+            return true;
+        }();
+    } // namespace
+
     // ---------------------------------------------------------------------------------
     // The control-frame dispatch and the twelve EGL forwarders (P5f, package fc)
     // ---------------------------------------------------------------------------------

MobileGL/MG_State/GLState/BufferState/BufferObject.cpp

@@ -66,6 +66,9 @@ namespace MobileGL::MG_State::GLState {
             if (!MG_Record::PersistentMapTracker::OnServerRole()) return;
             FatalLegacyBufferArmFromApplyThread(accessor);
         }
+#else
+        // P13 W5: no transport, no apply thread to refuse.
+        inline void RefuseLegacyBufferArmFromApplyThread(const char*) {}
 #endif
     }