Add editor panel host lifecycle contract

tests/UI/Editor/integration/README.md

@@ -28,6 +28,7 @@ Layout:
 - `shell/workspace_viewport_compose/`: workspace body external presentation compose only
 - `shell/workspace_interaction_basic/`: workspace unified interaction only
 - `state/panel_session_flow/`: panel session state flow only
+- `state/panel_host_lifecycle/`: panel host attach/detach/show/hide/activate/focus contract only
 - `state/layout_persistence/`: layout save/load/reset only
 - `state/shortcut_dispatch/`: shortcut match/suppression/dispatch only
 - `state/viewport_input_bridge_basic/`: viewport hover/focus/capture, local pointer coordinates, wheel/key/character bridge only
@@ -104,6 +105,11 @@ Scenarios:
   Executable: `XCUIEditorPanelSessionFlowValidation.exe`
   Scope: command dispatch + workspace controller + open/close/show/hide/activate
 
+- `editor.state.panel_host_lifecycle`
+  Build target: `editor_ui_panel_host_lifecycle_validation`
+  Executable: `XCUIEditorPanelHostLifecycleValidation.exe`
+  Scope: panel host attach/detach/show/hide/activate/focus lifecycle only; active/focus decoupling and hidden-tab attached state
+
 - `editor.state.layout_persistence`
   Build target: `editor_ui_layout_persistence_validation`
   Executable: `XCUIEditorLayoutPersistenceValidation.exe`
@@ -174,6 +180,9 @@ Selected controls:
 - `state/panel_session_flow/`
   Click `Hide Active / Show Doc A / Close Doc B / Open Doc B / Activate Details / Reset`, press `F12`.
 
+- `state/panel_host_lifecycle/`
+  Click `Hide Active / Close Doc B / Open Doc B / Activate Details / Focus Active / Clear Focus / Reset`, inspect `Events` and the three host cards, press `Capture` or `F12`.
+
 - `state/layout_persistence/`
   Click `Hide Active -> Save Layout -> Close Doc B -> Load Layout`, click `Load Invalid`, press `F12`.