EditorIntegration

Editor-side integration for typed scene (Tscn[T]) exports.

Installs an EditorInspectorPlugin; for Tscn[T] properties (recorded in SceneExportRegistry) it knows the required root node type T. Registered at the EDITOR init level (tool classes, isRuntime=false).

Status — the plugin pipeline (editor registration → editor_add_plugin → EditorPlugin._enter_tree → add_inspector_plugin → _can_handle/ _parse_property) is wired and the reusable primitives for a custom picker exist (Callable, Signals.connect, SignalRegistration.callDeferred, MethodRegistration.registerAction, a custom EditorProperty that renders).

Follow-up (deferred): a custom property editor that filters the scene picker by root type. Two blockers remain: (1) a child Control (e.g. a Button) added to an extension-created EditorProperty segfaults reading its theme on enter-tree ("theme items too early") — unresolved across pre-tree / _ready / call_deferred / minimal-addChild attempts; likely a theme-owner propagation issue for extension EditorPropertys. (2) The picker UI also needs engine methods absent from the curated codegen (PopupMenu.popup, DirAccess/PackedStringArray for scanning, EditorProperty.emit_changed). Until then the plugin stays inert and the default (unfiltered) PackedScene picker is used.