Blueprint-only installed plugin: packaging and module load

Verified 2026-10-13 on UE5.6.1CL44394996 Win64 Development. prepare_blueprint_package_host.py --tag BP56B --restore-default-policy copies the current compiled plugin and eight actual survey/source/entry/root dependency packages into a private project with no authored Source directory or Modules entry. RunUAT BuildCookRun builds, cooks, stages and archives /Engine/Maps/Entry; the actual inner BlueprintUI executable then exits0 after five seconds. verify_blueprint_package.py returns PASS_BLUEPRINT_ONLY_PACKAGE_AND_MODULE_LOAD.

The first BP56 cook/archive reported success in11.63s but its actual bootstrap exited3: InterfaceForge could not load because CommonUI was absent from the staged plugin manifest. No runtime acceptance was inferred from that build. Crash logs remain under that private archive's Saved/Crashes and are excluded from delivery.

Official BuildPlugin clears EnabledByDefault in its output descriptor. UnrealBuildTool treats a project plugin with the omitted field as enabled by default. Its default-versus-project code-plugin comparison therefore skipped the temporary game target and staged the stock UnrealGame receipt, which omitted CommonUI. These installed-engine source functions were inspected directly: BuildPluginCommand.Automation.cs, Plugins.cs IsEnabledByDefault and NativeProjects.cs RequiresTempTargetForCodePlugin.

Restoring the original EnabledByDefault=false in a fresh BP56B copy changed metadata only. UAT then explicitly generated its temporary BlueprintUI target/module files under Intermediate/Source, built the game and staged CommonUI. Package54.76s, no native/cook warning/error diagnostic. Actual game log confirms UE5.6.1, InterfaceForge/CommonUI mounting and one live IFSettingsSubsystem. Eight original Blueprint packages appear in the exact staging manifest; no optional SDK/inventory plugin enters the package. Core sources/assets remain identical to the64-file strict proof. UAT rebuilt generated plugin outputs; their before/after hashes are recorded instead of pretending the original generated binaries were unchanged.

The matching Review2 compiled archives preserve this original default policy. EP56/57/58 independently load23required reflected types/16distinct packages without authored game C++ or optional dependencies. They contain the same official binary/precompiled outputs as prior EB copies except the recorded descriptor restoration. Older Review ZIPs remain historical and should not be used for project-installed packaging.

This fixture proves installed-plugin packaging/module load, not a new playable interface or eight Blueprint instances running. Playable custom screen/entry/source/theme interactions have separate current example and IF5 receipts. Windows C++ build tools are required to compile Unreal's generated temporary target; developers author no game C++. Newer-engine and Shipping Blueprint-only packaging remain unverified. This is not whole-goal completion or hardware certification.