Add editor panel host lifecycle contract

new_editor/CMakeLists.txt

@@ -18,6 +18,7 @@ add_library(XCUIEditorLib STATIC
     src/Core/UIEditorDockHostInteraction.cpp
     src/Core/UIEditorMenuModel.cpp
     src/Core/UIEditorMenuSession.cpp
+    src/Core/UIEditorPanelHostLifecycle.cpp
     src/Core/UIEditorPanelRegistry.cpp
     src/Core/UIEditorShellCompose.cpp
     src/Core/UIEditorShellInteraction.cpp

new_editor/include/XCEditor/Core/UIEditorPanelHostLifecycle.h

@@ -0,0 +1,68 @@
+#pragma once
+
+#include <XCEditor/Core/UIEditorPanelRegistry.h>
+#include <XCEditor/Core/UIEditorWorkspaceSession.h>
+
+#include <cstdint>
+#include <string>
+#include <string_view>
+#include <vector>
+
+namespace XCEngine::UI::Editor {
+
+enum class UIEditorPanelHostLifecycleEventKind : std::uint8_t {
+    Attached = 0,
+    Detached,
+    Shown,
+    Hidden,
+    Activated,
+    Deactivated,
+    FocusGained,
+    FocusLost
+};
+
+std::string_view GetUIEditorPanelHostLifecycleEventKindName(
+    UIEditorPanelHostLifecycleEventKind kind);
+
+struct UIEditorPanelHostState {
+    std::string panelId = {};
+    bool attached = false;
+    bool visible = false;
+    bool active = false;
+    bool focused = false;
+};
+
+struct UIEditorPanelHostLifecycleEvent {
+    UIEditorPanelHostLifecycleEventKind kind = UIEditorPanelHostLifecycleEventKind::Attached;
+    std::string panelId = {};
+};
+
+struct UIEditorPanelHostLifecycleState {
+    std::vector<UIEditorPanelHostState> panelStates = {};
+};
+
+struct UIEditorPanelHostLifecycleRequest {
+    std::string focusedPanelId = {};
+};
+
+struct UIEditorPanelHostLifecycleFrame {
+    std::vector<UIEditorPanelHostState> panelStates = {};
+    std::vector<UIEditorPanelHostLifecycleEvent> events = {};
+};
+
+const UIEditorPanelHostState* FindUIEditorPanelHostState(
+    const UIEditorPanelHostLifecycleState& state,
+    std::string_view panelId);
+
+const UIEditorPanelHostState* FindUIEditorPanelHostState(
+    const UIEditorPanelHostLifecycleFrame& frame,
+    std::string_view panelId);
+
+UIEditorPanelHostLifecycleFrame UpdateUIEditorPanelHostLifecycle(
+    UIEditorPanelHostLifecycleState& state,
+    const UIEditorPanelRegistry& panelRegistry,
+    const UIEditorWorkspaceModel& workspace,
+    const UIEditorWorkspaceSession& session,
+    const UIEditorPanelHostLifecycleRequest& request = {});
+
+} // namespace XCEngine::UI::Editor

new_editor/src/Core/UIEditorPanelHostLifecycle.cpp

@@ -0,0 +1,207 @@
+#include <XCEditor/Core/UIEditorPanelHostLifecycle.h>
+
+#include <unordered_map>
+#include <unordered_set>
+#include <utility>
+
+namespace XCEngine::UI::Editor {
+
+namespace {
+
+using HostStateMap = std::unordered_map<std::string_view, const UIEditorPanelHostState*>;
+
+HostStateMap BuildHostStateMap(const std::vector<UIEditorPanelHostState>& states) {
+    HostStateMap map = {};
+    map.reserve(states.size());
+    for (const UIEditorPanelHostState& state : states) {
+        map.emplace(state.panelId, &state);
+    }
+    return map;
+}
+
+const UIEditorPanelHostState* FindHostState(
+    const std::vector<UIEditorPanelHostState>& states,
+    std::string_view panelId) {
+    for (const UIEditorPanelHostState& state : states) {
+        if (state.panelId == panelId) {
+            return &state;
+        }
+    }
+
+    return nullptr;
+}
+
+void AppendLeaveEvents(
+    std::vector<UIEditorPanelHostLifecycleEvent>& events,
+    const std::vector<UIEditorPanelHostState>& previousStates,
+    const HostStateMap& currentStateMap) {
+    auto appendCategory = [&](auto predicate, UIEditorPanelHostLifecycleEventKind kind) {
+        for (const UIEditorPanelHostState& previous : previousStates) {
+            const UIEditorPanelHostState emptyState = {};
+            const UIEditorPanelHostState& current =
+                currentStateMap.contains(previous.panelId)
+                    ? *currentStateMap.at(previous.panelId)
+                    : emptyState;
+            if (predicate(previous, current)) {
+                events.push_back({ kind, previous.panelId });
+            }
+        }
+    };
+
+    appendCategory(
+        [](const UIEditorPanelHostState& previous, const UIEditorPanelHostState& current) {
+            return previous.focused && !current.focused;
+        },
+        UIEditorPanelHostLifecycleEventKind::FocusLost);
+    appendCategory(
+        [](const UIEditorPanelHostState& previous, const UIEditorPanelHostState& current) {
+            return previous.active && !current.active;
+        },
+        UIEditorPanelHostLifecycleEventKind::Deactivated);
+    appendCategory(
+        [](const UIEditorPanelHostState& previous, const UIEditorPanelHostState& current) {
+            return previous.visible && !current.visible;
+        },
+        UIEditorPanelHostLifecycleEventKind::Hidden);
+    appendCategory(
+        [](const UIEditorPanelHostState& previous, const UIEditorPanelHostState& current) {
+            return previous.attached && !current.attached;
+        },
+        UIEditorPanelHostLifecycleEventKind::Detached);
+}
+
+void AppendEnterEvents(
+    std::vector<UIEditorPanelHostLifecycleEvent>& events,
+    const std::vector<UIEditorPanelHostState>& currentStates,
+    const HostStateMap& previousStateMap) {
+    auto appendCategory = [&](auto predicate, UIEditorPanelHostLifecycleEventKind kind) {
+        for (const UIEditorPanelHostState& current : currentStates) {
+            const UIEditorPanelHostState emptyState = {};
+            const UIEditorPanelHostState& previous =
+                previousStateMap.contains(current.panelId)
+                    ? *previousStateMap.at(current.panelId)
+                    : emptyState;
+            if (predicate(previous, current)) {
+                events.push_back({ kind, current.panelId });
+            }
+        }
+    };
+
+    appendCategory(
+        [](const UIEditorPanelHostState& previous, const UIEditorPanelHostState& current) {
+            return !previous.attached && current.attached;
+        },
+        UIEditorPanelHostLifecycleEventKind::Attached);
+    appendCategory(
+        [](const UIEditorPanelHostState& previous, const UIEditorPanelHostState& current) {
+            return !previous.visible && current.visible;
+        },
+        UIEditorPanelHostLifecycleEventKind::Shown);
+    appendCategory(
+        [](const UIEditorPanelHostState& previous, const UIEditorPanelHostState& current) {
+            return !previous.active && current.active;
+        },
+        UIEditorPanelHostLifecycleEventKind::Activated);
+    appendCategory(
+        [](const UIEditorPanelHostState& previous, const UIEditorPanelHostState& current) {
+            return !previous.focused && current.focused;
+        },
+        UIEditorPanelHostLifecycleEventKind::FocusGained);
+}
+
+std::vector<UIEditorPanelHostState> BuildResolvedPanelHostStates(
+    const UIEditorPanelRegistry& panelRegistry,
+    const UIEditorWorkspaceModel& workspace,
+    const UIEditorWorkspaceSession& session,
+    const UIEditorPanelHostLifecycleRequest& request) {
+    const std::vector<UIEditorWorkspaceVisiblePanel> visiblePanels =
+        CollectUIEditorWorkspaceVisiblePanels(workspace, session);
+    std::unordered_set<std::string_view> visiblePanelIds = {};
+    visiblePanelIds.reserve(visiblePanels.size());
+    for (const UIEditorWorkspaceVisiblePanel& panel : visiblePanels) {
+        visiblePanelIds.insert(panel.panelId);
+    }
+
+    std::vector<UIEditorPanelHostState> states = {};
+    states.reserve(panelRegistry.panels.size());
+    for (const UIEditorPanelDescriptor& descriptor : panelRegistry.panels) {
+        if (!ContainsUIEditorWorkspacePanel(workspace, descriptor.panelId)) {
+            continue;
+        }
+
+        const UIEditorPanelSessionState* sessionState =
+            FindUIEditorPanelSessionState(session, descriptor.panelId);
+        if (sessionState == nullptr) {
+            continue;
+        }
+
+        UIEditorPanelHostState state = {};
+        state.panelId = descriptor.panelId;
+        state.attached = sessionState->open;
+        state.visible = state.attached && visiblePanelIds.contains(state.panelId);
+        state.active = state.visible && workspace.activePanelId == state.panelId;
+        state.focused = state.active && request.focusedPanelId == state.panelId;
+        states.push_back(std::move(state));
+    }
+
+    return states;
+}
+
+} // namespace
+
+std::string_view GetUIEditorPanelHostLifecycleEventKindName(
+    UIEditorPanelHostLifecycleEventKind kind) {
+    switch (kind) {
+    case UIEditorPanelHostLifecycleEventKind::Attached:
+        return "Attached";
+    case UIEditorPanelHostLifecycleEventKind::Detached:
+        return "Detached";
+    case UIEditorPanelHostLifecycleEventKind::Shown:
+        return "Shown";
+    case UIEditorPanelHostLifecycleEventKind::Hidden:
+        return "Hidden";
+    case UIEditorPanelHostLifecycleEventKind::Activated:
+        return "Activated";
+    case UIEditorPanelHostLifecycleEventKind::Deactivated:
+        return "Deactivated";
+    case UIEditorPanelHostLifecycleEventKind::FocusGained:
+        return "FocusGained";
+    case UIEditorPanelHostLifecycleEventKind::FocusLost:
+        return "FocusLost";
+    }
+
+    return "Unknown";
+}
+
+const UIEditorPanelHostState* FindUIEditorPanelHostState(
+    const UIEditorPanelHostLifecycleState& state,
+    std::string_view panelId) {
+    return FindHostState(state.panelStates, panelId);
+}
+
+const UIEditorPanelHostState* FindUIEditorPanelHostState(
+    const UIEditorPanelHostLifecycleFrame& frame,
+    std::string_view panelId) {
+    return FindHostState(frame.panelStates, panelId);
+}
+
+UIEditorPanelHostLifecycleFrame UpdateUIEditorPanelHostLifecycle(
+    UIEditorPanelHostLifecycleState& state,
+    const UIEditorPanelRegistry& panelRegistry,
+    const UIEditorWorkspaceModel& workspace,
+    const UIEditorWorkspaceSession& session,
+    const UIEditorPanelHostLifecycleRequest& request) {
+    UIEditorPanelHostLifecycleFrame frame = {};
+    frame.panelStates =
+        BuildResolvedPanelHostStates(panelRegistry, workspace, session, request);
+
+    const HostStateMap previousStateMap = BuildHostStateMap(state.panelStates);
+    const HostStateMap currentStateMap = BuildHostStateMap(frame.panelStates);
+    AppendLeaveEvents(frame.events, state.panelStates, currentStateMap);
+    AppendEnterEvents(frame.events, frame.panelStates, previousStateMap);
+
+    state.panelStates = frame.panelStates;
+    return frame;
+}
+
+} // namespace XCEngine::UI::Editor

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`.
 

tests/UI/Editor/integration/state/CMakeLists.txt

@@ -1,4 +1,5 @@
 add_subdirectory(panel_session_flow)
+add_subdirectory(panel_host_lifecycle)
 add_subdirectory(layout_persistence)
 add_subdirectory(shortcut_dispatch)
 if(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/viewport_input_bridge_basic/CMakeLists.txt")

tests/UI/Editor/integration/state/panel_host_lifecycle/CMakeLists.txt

@@ -0,0 +1,31 @@
+add_executable(editor_ui_panel_host_lifecycle_validation WIN32
+    main.cpp
+)
+
+target_include_directories(editor_ui_panel_host_lifecycle_validation PRIVATE
+    ${CMAKE_SOURCE_DIR}/engine/include
+    ${CMAKE_SOURCE_DIR}/new_editor/include
+    ${CMAKE_SOURCE_DIR}/new_editor/app
+    ${CMAKE_SOURCE_DIR}/new_editor/src
+)
+
+target_compile_definitions(editor_ui_panel_host_lifecycle_validation PRIVATE
+    UNICODE
+    _UNICODE
+    XCENGINE_EDITOR_UI_TESTS_REPO_ROOT="${XCENGINE_EDITOR_UI_TESTS_REPO_ROOT_PATH}"
+)
+
+if(MSVC)
+    target_compile_options(editor_ui_panel_host_lifecycle_validation PRIVATE /utf-8 /FS)
+    set_property(TARGET editor_ui_panel_host_lifecycle_validation PROPERTY
+        MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>DLL")
+endif()
+
+target_link_libraries(editor_ui_panel_host_lifecycle_validation PRIVATE
+    XCUIEditorLib
+    XCUIEditorHost
+)
+
+set_target_properties(editor_ui_panel_host_lifecycle_validation PROPERTIES
+    OUTPUT_NAME "XCUIEditorPanelHostLifecycleValidation"
+)

tests/UI/Editor/integration/state/panel_host_lifecycle/captures/.gitkeep

@@ -0,0 +1 @@
+

tests/UI/Editor/integration/state/panel_host_lifecycle/main.cpp

@@ -0,0 +1,659 @@
+#ifndef NOMINMAX
+#define NOMINMAX
+#endif
+
+#include <XCEditor/Core/UIEditorPanelHostLifecycle.h>
+#include <XCEditor/Core/UIEditorWorkspaceController.h>
+#include "Host/AutoScreenshot.h"
+#include "Host/NativeRenderer.h"
+
+#include <XCEngine/UI/DrawData.h>
+
+#include <windows.h>
+#include <windowsx.h>
+
+#include <algorithm>
+#include <filesystem>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <utility>
+#include <vector>
+
+#ifndef XCENGINE_EDITOR_UI_TESTS_REPO_ROOT
+#define XCENGINE_EDITOR_UI_TESTS_REPO_ROOT "."
+#endif
+
+namespace {
+
+using XCEngine::UI::UIColor;
+using XCEngine::UI::UIDrawData;
+using XCEngine::UI::UIDrawList;
+using XCEngine::UI::UIPoint;
+using XCEngine::UI::UIRect;
+using XCEngine::UI::Editor::BuildDefaultUIEditorWorkspaceController;
+using XCEngine::UI::Editor::BuildUIEditorWorkspacePanel;
+using XCEngine::UI::Editor::BuildUIEditorWorkspaceSplit;
+using XCEngine::UI::Editor::BuildUIEditorWorkspaceTabStack;
+using XCEngine::UI::Editor::CollectUIEditorWorkspaceVisiblePanels;
+using XCEngine::UI::Editor::FindUIEditorPanelHostState;
+using XCEngine::UI::Editor::GetUIEditorPanelHostLifecycleEventKindName;
+using XCEngine::UI::Editor::GetUIEditorWorkspaceCommandStatusName;
+using XCEngine::UI::Editor::Host::AutoScreenshotController;
+using XCEngine::UI::Editor::Host::NativeRenderer;
+using XCEngine::UI::Editor::UIEditorPanelHostLifecycleFrame;
+using XCEngine::UI::Editor::UIEditorPanelHostLifecycleRequest;
+using XCEngine::UI::Editor::UIEditorPanelHostLifecycleState;
+using XCEngine::UI::Editor::UIEditorPanelRegistry;
+using XCEngine::UI::Editor::UIEditorWorkspaceCommand;
+using XCEngine::UI::Editor::UIEditorWorkspaceCommandKind;
+using XCEngine::UI::Editor::UIEditorWorkspaceController;
+using XCEngine::UI::Editor::UIEditorWorkspaceModel;
+using XCEngine::UI::Editor::UIEditorWorkspaceSplitAxis;
+using XCEngine::UI::Editor::UpdateUIEditorPanelHostLifecycle;
+
+constexpr const wchar_t* kWindowClassName = L"XCUIEditorPanelHostLifecycleValidation";
+constexpr const wchar_t* kWindowTitle = L"XCUI Editor | Panel Host Lifecycle";
+
+constexpr UIColor kWindowBg(0.12f, 0.12f, 0.12f, 1.0f);
+constexpr UIColor kCardBg(0.18f, 0.18f, 0.18f, 1.0f);
+constexpr UIColor kCardBorder(0.29f, 0.29f, 0.29f, 1.0f);
+constexpr UIColor kTextPrimary(0.94f, 0.94f, 0.94f, 1.0f);
+constexpr UIColor kTextMuted(0.72f, 0.72f, 0.72f, 1.0f);
+constexpr UIColor kTextWeak(0.56f, 0.56f, 0.56f, 1.0f);
+constexpr UIColor kSuccess(0.45f, 0.72f, 0.49f, 1.0f);
+constexpr UIColor kWarning(0.81f, 0.67f, 0.35f, 1.0f);
+constexpr UIColor kDanger(0.78f, 0.36f, 0.36f, 1.0f);
+constexpr UIColor kAccent(0.68f, 0.72f, 0.78f, 1.0f);
+constexpr UIColor kButtonBg(0.25f, 0.25f, 0.25f, 1.0f);
+constexpr UIColor kButtonHover(0.33f, 0.33f, 0.33f, 1.0f);
+constexpr UIColor kButtonBorder(0.46f, 0.46f, 0.46f, 1.0f);
+constexpr UIColor kPreviewCard(0.15f, 0.15f, 0.15f, 1.0f);
+constexpr UIColor kAttachedBorder(0.54f, 0.64f, 0.74f, 1.0f);
+constexpr UIColor kVisibleBorder(0.46f, 0.72f, 0.50f, 1.0f);
+constexpr UIColor kActiveBorder(0.86f, 0.76f, 0.46f, 1.0f);
+
+enum class ActionId : unsigned char {
+    HideActive = 0,
+    CloseDocB,
+    OpenDocB,
+    ActivateDetails,
+    FocusActive,
+    ClearFocus,
+    Reset,
+    Capture
+};
+
+struct ButtonState {
+    ActionId action = ActionId::HideActive;
+    std::string label = {};
+    UIRect rect = {};
+    bool hovered = false;
+};
+
+std::filesystem::path ResolveRepoRootPath() {
+    std::string root = XCENGINE_EDITOR_UI_TESTS_REPO_ROOT;
+    if (root.size() >= 2u && root.front() == '"' && root.back() == '"') {
+        root = root.substr(1u, root.size() - 2u);
+    }
+    return std::filesystem::path(root).lexically_normal();
+}
+
+UIEditorPanelRegistry BuildPanelRegistry() {
+    UIEditorPanelRegistry registry = {};
+    registry.panels = {
+        { "doc-a", "Document A", {}, true, true, true },
+        { "doc-b", "Document B", {}, true, true, true },
+        { "details", "Details", {}, true, true, true }
+    };
+    return registry;
+}
+
+UIEditorWorkspaceModel BuildWorkspace() {
+    UIEditorWorkspaceModel workspace = {};
+    workspace.root = BuildUIEditorWorkspaceSplit(
+        "root-split",
+        UIEditorWorkspaceSplitAxis::Horizontal,
+        0.66f,
+        BuildUIEditorWorkspaceTabStack(
+            "document-tabs",
+            {
+                BuildUIEditorWorkspacePanel("doc-a-node", "doc-a", "Document A", true),
+                BuildUIEditorWorkspacePanel("doc-b-node", "doc-b", "Document B", true)
+            },
+            0u),
+        BuildUIEditorWorkspacePanel("details-node", "details", "Details", true));
+    workspace.activePanelId = "doc-a";
+    return workspace;
+}
+
+bool ContainsPoint(const UIRect& rect, float x, float y) {
+    return x >= rect.x &&
+        x <= rect.x + rect.width &&
+        y >= rect.y &&
+        y <= rect.y + rect.height;
+}
+
+std::string JoinVisiblePanelIds(const UIEditorWorkspaceController& controller) {
+    const auto panels =
+        CollectUIEditorWorkspaceVisiblePanels(controller.GetWorkspace(), controller.GetSession());
+    if (panels.empty()) {
+        return "(none)";
+    }
+
+    std::ostringstream stream = {};
+    for (std::size_t index = 0; index < panels.size(); ++index) {
+        if (index > 0u) {
+            stream << ", ";
+        }
+        stream << panels[index].panelId;
+    }
+    return stream.str();
+}
+
+std::string FormatBool(bool value) {
+    return value ? "true" : "false";
+}
+
+std::string FormatEvents(const UIEditorPanelHostLifecycleFrame& frame) {
+    if (frame.events.empty()) {
+        return "(none)";
+    }
+
+    std::ostringstream stream = {};
+    for (std::size_t index = 0; index < frame.events.size(); ++index) {
+        if (index > 0u) {
+            stream << " | ";
+        }
+        stream << GetUIEditorPanelHostLifecycleEventKindName(frame.events[index].kind)
+               << ":" << frame.events[index].panelId;
+    }
+    return stream.str();
+}
+
+UIColor ResolveFlagColor(bool value, const UIColor& onColor) {
+    return value ? onColor : kTextWeak;
+}
+
+UIColor ResolveHostBorderColor(bool attached, bool visible, bool active, bool focused) {
+    if (focused) {
+        return kActiveBorder;
+    }
+    if (active) {
+        return kActiveBorder;
+    }
+    if (visible) {
+        return kVisibleBorder;
+    }
+    if (attached) {
+        return kAttachedBorder;
+    }
+    return kCardBorder;
+}
+
+void DrawCard(
+    UIDrawList& drawList,
+    const UIRect& rect,
+    std::string_view title,
+    std::string_view subtitle = {}) {
+    drawList.AddFilledRect(rect, kCardBg, 12.0f);
+    drawList.AddRectOutline(rect, kCardBorder, 1.0f, 12.0f);
+    drawList.AddText(UIPoint(rect.x + 18.0f, rect.y + 16.0f), std::string(title), kTextPrimary, 17.0f);
+    if (!subtitle.empty()) {
+        drawList.AddText(UIPoint(rect.x + 18.0f, rect.y + 42.0f), std::string(subtitle), kTextMuted, 12.0f);
+    }
+}
+
+void DrawButton(UIDrawList& drawList, const ButtonState& button) {
+    drawList.AddFilledRect(button.rect, button.hovered ? kButtonHover : kButtonBg, 8.0f);
+    drawList.AddRectOutline(button.rect, kButtonBorder, 1.0f, 8.0f);
+    drawList.AddText(UIPoint(button.rect.x + 12.0f, button.rect.y + 10.0f), button.label, kTextPrimary, 12.0f);
+}
+
+void DrawHostStateCard(
+    UIDrawList& drawList,
+    const UIRect& rect,
+    std::string_view title,
+    const XCEngine::UI::Editor::UIEditorPanelHostState* state) {
+    const bool attached = state != nullptr && state->attached;
+    const bool visible = state != nullptr && state->visible;
+    const bool active = state != nullptr && state->active;
+    const bool focused = state != nullptr && state->focused;
+
+    drawList.AddFilledRect(rect, kPreviewCard, 10.0f);
+    drawList.AddRectOutline(
+        rect,
+        ResolveHostBorderColor(attached, visible, active, focused),
+        active || focused ? 2.0f : 1.0f,
+        10.0f);
+    drawList.AddText(UIPoint(rect.x + 16.0f, rect.y + 14.0f), std::string(title), kTextPrimary, 16.0f);
+
+    float lineY = rect.y + 48.0f;
+    auto addFlag = [&](std::string_view label, bool value, const UIColor& color) {
+        drawList.AddText(
+            UIPoint(rect.x + 16.0f, lineY),
+            std::string(label) + ": " + (value ? "true" : "false"),
+            ResolveFlagColor(value, color),
+            12.0f);
+        lineY += 22.0f;
+    };
+
+    addFlag("Attached", attached, kAccent);
+    addFlag("Visible", visible, kSuccess);
+    addFlag("Active", active, kWarning);
+    addFlag("Focused", focused, kActiveBorder);
+
+    std::string footer = {};
+    if (!attached) {
+        footer = "host 已 detached";
+    } else if (!visible) {
+        footer = "host 保留 attach，但当前不在屏幕上";
+    } else if (focused) {
+        footer = "当前 host 已 visible + active + focused";
+    } else if (active) {
+        footer = "当前 host 已 active，但还没 focus";
+    } else {
+        footer = "当前 host 只处于 attached/visible";
+    }
+    drawList.AddText(UIPoint(rect.x + 16.0f, rect.y + rect.height - 26.0f), footer, kTextMuted, 11.0f);
+}
+
+class ScenarioApp {
+public:
+    int Run(HINSTANCE hInstance, int nCmdShow) {
+        if (!Initialize(hInstance, nCmdShow)) {
+            Shutdown();
+            return 1;
+        }
+
+        MSG message = {};
+        while (message.message != WM_QUIT) {
+            if (PeekMessageW(&message, nullptr, 0U, 0U, PM_REMOVE)) {
+                TranslateMessage(&message);
+                DispatchMessageW(&message);
+                continue;
+            }
+
+            RenderFrame();
+            Sleep(8);
+        }
+
+        Shutdown();
+        return static_cast<int>(message.wParam);
+    }
+
+private:
+    static LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) {
+        if (message == WM_NCCREATE) {
+            const auto* createStruct = reinterpret_cast<CREATESTRUCTW*>(lParam);
+            auto* app = reinterpret_cast<ScenarioApp*>(createStruct->lpCreateParams);
+            SetWindowLongPtrW(hwnd, GWLP_USERDATA, reinterpret_cast<LONG_PTR>(app));
+            return TRUE;
+        }
+
+        auto* app = reinterpret_cast<ScenarioApp*>(GetWindowLongPtrW(hwnd, GWLP_USERDATA));
+        switch (message) {
+        case WM_SIZE:
+            if (app != nullptr && wParam != SIZE_MINIMIZED) {
+                app->OnResize(static_cast<UINT>(LOWORD(lParam)), static_cast<UINT>(HIWORD(lParam)));
+            }
+            return 0;
+        case WM_PAINT:
+            if (app != nullptr) {
+                PAINTSTRUCT paintStruct = {};
+                BeginPaint(hwnd, &paintStruct);
+                app->RenderFrame();
+                EndPaint(hwnd, &paintStruct);
+                return 0;
+            }
+            break;
+        case WM_MOUSEMOVE:
+            if (app != nullptr) {
+                app->HandleMouseMove(
+                    static_cast<float>(GET_X_LPARAM(lParam)),
+                    static_cast<float>(GET_Y_LPARAM(lParam)));
+                return 0;
+            }
+            break;
+        case WM_LBUTTONUP:
+            if (app != nullptr) {
+                app->HandleClick(
+                    static_cast<float>(GET_X_LPARAM(lParam)),
+                    static_cast<float>(GET_Y_LPARAM(lParam)));
+                return 0;
+            }
+            break;
+        case WM_KEYDOWN:
+        case WM_SYSKEYDOWN:
+            if (app != nullptr && wParam == VK_F12) {
+                app->m_autoScreenshot.RequestCapture("manual_f12");
+                return 0;
+            }
+            break;
+        case WM_ERASEBKGND:
+            return 1;
+        case WM_DESTROY:
+            if (app != nullptr) {
+                app->m_hwnd = nullptr;
+            }
+            PostQuitMessage(0);
+            return 0;
+        default:
+            break;
+        }
+
+        return DefWindowProcW(hwnd, message, wParam, lParam);
+    }
+
+    bool Initialize(HINSTANCE hInstance, int nCmdShow) {
+        m_hInstance = hInstance;
+        ResetScenario();
+
+        WNDCLASSEXW windowClass = {};
+        windowClass.cbSize = sizeof(windowClass);
+        windowClass.style = CS_HREDRAW | CS_VREDRAW;
+        windowClass.lpfnWndProc = &ScenarioApp::WndProc;
+        windowClass.hInstance = hInstance;
+        windowClass.hCursor = LoadCursorW(nullptr, IDC_ARROW);
+        windowClass.lpszClassName = kWindowClassName;
+
+        m_windowClassAtom = RegisterClassExW(&windowClass);
+        if (m_windowClassAtom == 0) {
+            return false;
+        }
+
+        m_hwnd = CreateWindowExW(
+            0,
+            kWindowClassName,
+            kWindowTitle,
+            WS_OVERLAPPEDWINDOW | WS_VISIBLE,
+            CW_USEDEFAULT,
+            CW_USEDEFAULT,
+            1440,
+            920,
+            nullptr,
+            nullptr,
+            hInstance,
+            this);
+        if (m_hwnd == nullptr) {
+            return false;
+        }
+
+        ShowWindow(m_hwnd, nCmdShow);
+        UpdateWindow(m_hwnd);
+
+        if (!m_renderer.Initialize(m_hwnd)) {
+            return false;
+        }
+
+        m_captureRoot =
+            ResolveRepoRootPath() /
+            "tests/UI/Editor/integration/state/panel_host_lifecycle/captures";
+        m_autoScreenshot.Initialize(m_captureRoot);
+        return true;
+    }
+
+    void Shutdown() {
+        m_autoScreenshot.Shutdown();
+        m_renderer.Shutdown();
+
+        if (m_hwnd != nullptr) {
+            DestroyWindow(m_hwnd);
+            m_hwnd = nullptr;
+        }
+
+        if (m_windowClassAtom != 0) {
+            UnregisterClassW(kWindowClassName, m_hInstance);
+            m_windowClassAtom = 0;
+        }
+    }
+
+    void ResetScenario() {
+        m_controller =
+            BuildDefaultUIEditorWorkspaceController(BuildPanelRegistry(), BuildWorkspace());
+        m_lifecycleState = {};
+        m_focusRequestPanelId.clear();
+        RefreshLifecycle(
+            "Ready",
+            "已重置。先看 doc-b：它默认是 attached，但因为不是选中 tab，所以 visible=false。");
+    }
+
+    void RefreshLifecycle(std::string status, std::string message) {
+        m_lifecycleFrame = UpdateUIEditorPanelHostLifecycle(
+            m_lifecycleState,
+            m_controller.GetPanelRegistry(),
+            m_controller.GetWorkspace(),
+            m_controller.GetSession(),
+            UIEditorPanelHostLifecycleRequest{ m_focusRequestPanelId });
+        m_lastStatus = std::move(status);
+        m_lastMessage = std::move(message);
+    }
+
+    void UpdateLayout() {
+        RECT clientRect = {};
+        GetClientRect(m_hwnd, &clientRect);
+        const float width = static_cast<float>((std::max)(clientRect.right - clientRect.left, 1L));
+        const float height = static_cast<float>((std::max)(clientRect.bottom - clientRect.top, 1L));
+
+        constexpr float padding = 20.0f;
+        constexpr float leftWidth = 440.0f;
+        m_introRect = UIRect(padding, padding, leftWidth, 208.0f);
+        m_controlsRect = UIRect(padding, 244.0f, leftWidth, 244.0f);
+        m_stateRect = UIRect(padding, 504.0f, leftWidth, height - 524.0f);
+        m_previewRect = UIRect(leftWidth + padding * 2.0f, padding, width - leftWidth - padding * 3.0f, height - padding * 2.0f);
+
+        const float buttonLeft = m_controlsRect.x + 16.0f;
+        const float buttonTop = m_controlsRect.y + 62.0f;
+        const float buttonWidth = (m_controlsRect.width - 32.0f - 16.0f) * 0.5f;
+        const float buttonHeight = 34.0f;
+        const float rowGap = 10.0f;
+        m_buttons = {
+            { ActionId::HideActive, "Hide Active", UIRect(buttonLeft, buttonTop, buttonWidth, buttonHeight), false },
+            { ActionId::CloseDocB, "Close Doc B", UIRect(buttonLeft + buttonWidth + 16.0f, buttonTop, buttonWidth, buttonHeight), false },
+            { ActionId::OpenDocB, "Open Doc B", UIRect(buttonLeft, buttonTop + buttonHeight + rowGap, buttonWidth, buttonHeight), false },
+            { ActionId::ActivateDetails, "Activate Details", UIRect(buttonLeft + buttonWidth + 16.0f, buttonTop + buttonHeight + rowGap, buttonWidth, buttonHeight), false },
+            { ActionId::FocusActive, "Focus Active", UIRect(buttonLeft, buttonTop + (buttonHeight + rowGap) * 2.0f, buttonWidth, buttonHeight), false },
+            { ActionId::ClearFocus, "Clear Focus", UIRect(buttonLeft + buttonWidth + 16.0f, buttonTop + (buttonHeight + rowGap) * 2.0f, buttonWidth, buttonHeight), false },
+            { ActionId::Reset, "Reset", UIRect(buttonLeft, buttonTop + (buttonHeight + rowGap) * 3.0f, buttonWidth, buttonHeight), false },
+            { ActionId::Capture, "Capture(F12)", UIRect(buttonLeft + buttonWidth + 16.0f, buttonTop + (buttonHeight + rowGap) * 3.0f, buttonWidth, buttonHeight), false }
+        };
+
+        const float previewPadding = 24.0f;
+        const float hostCardGap = 18.0f;
+        const float docWidth = (m_previewRect.width - previewPadding * 2.0f - hostCardGap) * 0.56f;
+        const float sideWidth = m_previewRect.width - previewPadding * 2.0f - hostCardGap - docWidth;
+        const float cardTop = m_previewRect.y + 76.0f;
+        const float cardHeight = (m_previewRect.height - 116.0f - hostCardGap) * 0.5f;
+        m_docARect = UIRect(m_previewRect.x + previewPadding, cardTop, docWidth, cardHeight);
+        m_docBRect = UIRect(m_previewRect.x + previewPadding, cardTop + cardHeight + hostCardGap, docWidth, cardHeight);
+        m_detailsRect = UIRect(m_docARect.x + docWidth + hostCardGap, cardTop, sideWidth, cardHeight * 2.0f + hostCardGap);
+    }
+
+    void OnResize(UINT width, UINT height) {
+        m_renderer.Resize(width, height);
+        InvalidateRect(m_hwnd, nullptr, FALSE);
+    }
+
+    void HandleMouseMove(float x, float y) {
+        UpdateLayout();
+        for (ButtonState& button : m_buttons) {
+            button.hovered = ContainsPoint(button.rect, x, y);
+        }
+    }
+
+    void HandleClick(float x, float y) {
+        UpdateLayout();
+        for (const ButtonState& button : m_buttons) {
+            if (ContainsPoint(button.rect, x, y)) {
+                ExecuteAction(button.action);
+                return;
+            }
+        }
+    }
+
+    void ExecuteAction(ActionId action) {
+        if (action == ActionId::Reset) {
+            ResetScenario();
+            return;
+        }
+
+        if (action == ActionId::Capture) {
+            m_autoScreenshot.RequestCapture("manual_button");
+            m_lastStatus = "Ready";
+            m_lastMessage = "截图已排队，输出到 tests/UI/Editor/integration/state/panel_host_lifecycle/captures/。";
+            return;
+        }
+
+        if (action == ActionId::FocusActive) {
+            m_focusRequestPanelId = m_controller.GetWorkspace().activePanelId;
+            RefreshLifecycle(
+                "Focus",
+                m_focusRequestPanelId.empty()
+                    ? "当前没有 active panel 可 focus。"
+                    : "已把 focus request 指向当前 active panel。");
+            return;
+        }
+
+        if (action == ActionId::ClearFocus) {
+            m_focusRequestPanelId.clear();
+            RefreshLifecycle("Focus", "已清空 focus request。");
+            return;
+        }
+
+        UIEditorWorkspaceCommand command = {};
+        switch (action) {
+        case ActionId::HideActive:
+            command.kind = UIEditorWorkspaceCommandKind::HidePanel;
+            command.panelId = m_controller.GetWorkspace().activePanelId;
+            break;
+        case ActionId::CloseDocB:
+            command.kind = UIEditorWorkspaceCommandKind::ClosePanel;
+            command.panelId = "doc-b";
+            break;
+        case ActionId::OpenDocB:
+            command.kind = UIEditorWorkspaceCommandKind::OpenPanel;
+            command.panelId = "doc-b";
+            break;
+        case ActionId::ActivateDetails:
+            command.kind = UIEditorWorkspaceCommandKind::ActivatePanel;
+            command.panelId = "details";
+            break;
+        default:
+            return;
+        }
+
+        const auto result = m_controller.Dispatch(command);
+        RefreshLifecycle(
+            std::string(GetUIEditorWorkspaceCommandStatusName(result.status)),
+            result.message);
+    }
+
+    void RenderFrame() {
+        UpdateLayout();
+
+        RECT clientRect = {};
+        GetClientRect(m_hwnd, &clientRect);
+        const float width = static_cast<float>((std::max)(clientRect.right - clientRect.left, 1L));
+        const float height = static_cast<float>((std::max)(clientRect.bottom - clientRect.top, 1L));
+
+        UIDrawData drawData = {};
+        UIDrawList& drawList = drawData.EmplaceDrawList("PanelHostLifecycle");
+        drawList.AddFilledRect(UIRect(0.0f, 0.0f, width, height), kWindowBg);
+
+        DrawCard(drawList, m_introRect, "这个测试验证什么功能", "只验证 Editor panel host lifecycle contract，不做业务面板。");
+        drawList.AddText(UIPoint(m_introRect.x + 18.0f, m_introRect.y + 72.0f), "1. 验证 attach/detach 由 panel open/close 驱动，而不是由 visible 驱动。", kTextPrimary, 12.0f);
+        drawList.AddText(UIPoint(m_introRect.x + 18.0f, m_introRect.y + 94.0f), "2. 验证非选中 tab 依然 attached，但 visible=false。", kTextPrimary, 12.0f);
+        drawList.AddText(UIPoint(m_introRect.x + 18.0f, m_introRect.y + 116.0f), "3. 验证 active 与 focused 是两层不同状态，focus 由外部 request 决定。", kTextPrimary, 12.0f);
+        drawList.AddText(UIPoint(m_introRect.x + 18.0f, m_introRect.y + 138.0f), "4. 验证 hide/close/reopen/activate 会输出稳定的 lifecycle events。", kTextPrimary, 12.0f);
+        drawList.AddText(UIPoint(m_introRect.x + 18.0f, m_introRect.y + 164.0f), "建议操作：先看 doc-b 默认 attached 但 hidden；再点 Hide Active / Focus Active / Close Doc B / Open Doc B。", kTextWeak, 11.0f);
+
+        DrawCard(drawList, m_controlsRect, "操作", "只保留这组 contract 必要的按钮。");
+        for (const ButtonState& button : m_buttons) {
+            DrawButton(drawList, button);
+        }
+
+        DrawCard(drawList, m_stateRect, "状态", "重点检查 host flags 和本帧 lifecycle events。");
+        float stateY = m_stateRect.y + 66.0f;
+        auto addStateLine = [&](std::string label, std::string value, const UIColor& color, float fontSize = 12.0f) {
+            drawList.AddText(UIPoint(m_stateRect.x + 18.0f, stateY), std::move(label) + ": " + std::move(value), color, fontSize);
+            stateY += 20.0f;
+        };
+
+        addStateLine("Active Panel", m_controller.GetWorkspace().activePanelId.empty() ? "(none)" : m_controller.GetWorkspace().activePanelId, kTextPrimary, 11.0f);
+        addStateLine("Focus Request", m_focusRequestPanelId.empty() ? "(none)" : m_focusRequestPanelId, m_focusRequestPanelId.empty() ? kTextMuted : kWarning, 11.0f);
+        addStateLine("Visible Panels", JoinVisiblePanelIds(m_controller), kTextPrimary, 11.0f);
+        const UIColor resultColor =
+            m_lastStatus == "Rejected" ? kDanger :
+            (m_lastStatus == "Ready" ? kWarning : kSuccess);
+        addStateLine("Result", m_lastStatus, resultColor);
+        drawList.AddText(UIPoint(m_stateRect.x + 18.0f, stateY + 4.0f), m_lastMessage, kTextMuted, 11.0f);
+        stateY += 32.0f;
+        addStateLine("Events", FormatEvents(m_lifecycleFrame), kAccent, 11.0f);
+
+        const auto* docA = FindUIEditorPanelHostState(m_lifecycleFrame, "doc-a");
+        const auto* docB = FindUIEditorPanelHostState(m_lifecycleFrame, "doc-b");
+        const auto* details = FindUIEditorPanelHostState(m_lifecycleFrame, "details");
+        auto formatHostLine = [](std::string_view panelId, const XCEngine::UI::Editor::UIEditorPanelHostState* state) {
+            if (state == nullptr) {
+                return std::string(panelId) + " missing";
+            }
+            return std::string(panelId) +
+                " a=" + (state->attached ? "1" : "0") +
+                " v=" + (state->visible ? "1" : "0") +
+                " act=" + (state->active ? "1" : "0") +
+                " f=" + (state->focused ? "1" : "0");
+        };
+        addStateLine("doc-a", formatHostLine("doc-a", docA), kTextWeak, 11.0f);
+        addStateLine("doc-b", formatHostLine("doc-b", docB), kTextWeak, 11.0f);
+        addStateLine("details", formatHostLine("details", details), kTextWeak, 11.0f);
+        addStateLine(
+            "Screenshot",
+            m_autoScreenshot.HasPendingCapture()
+                ? "截图排队中..."
+                : (m_autoScreenshot.GetLastCaptureSummary().empty()
+                    ? std::string("F12 或 Capture -> captures/")
+                    : m_autoScreenshot.GetLastCaptureSummary()),
+            kTextWeak,
+            11.0f);
+
+        DrawCard(drawList, m_previewRect, "Preview", "这里不是业务面板，只把 host state 直接可视化。");
+        DrawHostStateCard(drawList, m_docARect, "Document A", docA);
+        DrawHostStateCard(drawList, m_docBRect, "Document B", docB);
+        DrawHostStateCard(drawList, m_detailsRect, "Details", details);
+
+        const bool framePresented = m_renderer.Render(drawData);
+        m_autoScreenshot.CaptureIfRequested(
+            m_renderer,
+            drawData,
+            static_cast<unsigned int>(width),
+            static_cast<unsigned int>(height),
+            framePresented);
+    }
+
+    HINSTANCE m_hInstance = nullptr;
+    HWND m_hwnd = nullptr;
+    ATOM m_windowClassAtom = 0;
+    NativeRenderer m_renderer = {};
+    AutoScreenshotController m_autoScreenshot = {};
+    std::filesystem::path m_captureRoot = {};
+    UIEditorWorkspaceController m_controller = {};
+    UIEditorPanelHostLifecycleState m_lifecycleState = {};
+    UIEditorPanelHostLifecycleFrame m_lifecycleFrame = {};
+    std::string m_focusRequestPanelId = {};
+    std::string m_lastStatus = {};
+    std::string m_lastMessage = {};
+    UIRect m_introRect = {};
+    UIRect m_controlsRect = {};
+    UIRect m_stateRect = {};
+    UIRect m_previewRect = {};
+    UIRect m_docARect = {};
+    UIRect m_docBRect = {};
+    UIRect m_detailsRect = {};
+    std::vector<ButtonState> m_buttons = {};
+};
+
+} // namespace
+
+int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, LPWSTR, int nCmdShow) {
+    return ScenarioApp().Run(hInstance, nCmdShow);
+}

tests/UI/Editor/unit/CMakeLists.txt

@@ -9,6 +9,7 @@ set(EDITOR_UI_UNIT_TEST_SOURCES
     test_ui_editor_menu_session.cpp
     test_ui_editor_menu_bar.cpp
     test_ui_editor_menu_popup.cpp
+    test_ui_editor_panel_host_lifecycle.cpp
     test_ui_editor_panel_registry.cpp
     test_ui_editor_shell_compose.cpp
     test_ui_editor_shell_interaction.cpp

tests/UI/Editor/unit/test_ui_editor_panel_host_lifecycle.cpp

@@ -0,0 +1,246 @@
+#include <gtest/gtest.h>
+
+#include <XCEditor/Core/UIEditorPanelHostLifecycle.h>
+
+namespace {
+
+using XCEngine::UI::Editor::BuildDefaultUIEditorWorkspaceSession;
+using XCEngine::UI::Editor::BuildUIEditorWorkspacePanel;
+using XCEngine::UI::Editor::BuildUIEditorWorkspaceSplit;
+using XCEngine::UI::Editor::BuildUIEditorWorkspaceTabStack;
+using XCEngine::UI::Editor::FindUIEditorPanelHostState;
+using XCEngine::UI::Editor::GetUIEditorPanelHostLifecycleEventKindName;
+using XCEngine::UI::Editor::TryCloseUIEditorWorkspacePanel;
+using XCEngine::UI::Editor::TryHideUIEditorWorkspacePanel;
+using XCEngine::UI::Editor::TryOpenUIEditorWorkspacePanel;
+using XCEngine::UI::Editor::UIEditorPanelHostLifecycleRequest;
+using XCEngine::UI::Editor::UIEditorPanelHostLifecycleState;
+using XCEngine::UI::Editor::UIEditorPanelRegistry;
+using XCEngine::UI::Editor::UIEditorWorkspaceModel;
+using XCEngine::UI::Editor::UIEditorWorkspaceSession;
+using XCEngine::UI::Editor::UIEditorWorkspaceSplitAxis;
+using XCEngine::UI::Editor::UpdateUIEditorPanelHostLifecycle;
+
+UIEditorPanelRegistry BuildPanelRegistry() {
+    UIEditorPanelRegistry registry = {};
+    registry.panels = {
+        { "doc-a", "Document A", {}, true, true, true },
+        { "doc-b", "Document B", {}, true, true, true },
+        { "details", "Details", {}, true, true, true }
+    };
+    return registry;
+}
+
+UIEditorWorkspaceModel BuildWorkspace() {
+    UIEditorWorkspaceModel workspace = {};
+    workspace.root = BuildUIEditorWorkspaceSplit(
+        "root-split",
+        UIEditorWorkspaceSplitAxis::Horizontal,
+        0.66f,
+        BuildUIEditorWorkspaceTabStack(
+            "document-tabs",
+            {
+                BuildUIEditorWorkspacePanel("doc-a-node", "doc-a", "Document A", true),
+                BuildUIEditorWorkspacePanel("doc-b-node", "doc-b", "Document B", true)
+            },
+            0u),
+        BuildUIEditorWorkspacePanel("details-node", "details", "Details", true));
+    workspace.activePanelId = "doc-a";
+    return workspace;
+}
+
+std::vector<std::string> FormatEvents(
+    const std::vector<XCEngine::UI::Editor::UIEditorPanelHostLifecycleEvent>& events) {
+    std::vector<std::string> formatted = {};
+    formatted.reserve(events.size());
+    for (const auto& event : events) {
+        formatted.push_back(
+            std::string(GetUIEditorPanelHostLifecycleEventKindName(event.kind)) + ":" + event.panelId);
+    }
+    return formatted;
+}
+
+} // namespace
+
+TEST(UIEditorPanelHostLifecycleTest, InitialFrameResolvesAttachedVisibleActiveAndFocusedPanels) {
+    const UIEditorPanelRegistry registry = BuildPanelRegistry();
+    const UIEditorWorkspaceModel workspace = BuildWorkspace();
+    const UIEditorWorkspaceSession session =
+        BuildDefaultUIEditorWorkspaceSession(registry, workspace);
+
+    UIEditorPanelHostLifecycleState lifecycleState = {};
+    const auto frame = UpdateUIEditorPanelHostLifecycle(
+        lifecycleState,
+        registry,
+        workspace,
+        session,
+        UIEditorPanelHostLifecycleRequest{ "doc-a" });
+
+    ASSERT_EQ(frame.panelStates.size(), 3u);
+    const auto* docA = FindUIEditorPanelHostState(frame, "doc-a");
+    const auto* docB = FindUIEditorPanelHostState(frame, "doc-b");
+    const auto* details = FindUIEditorPanelHostState(frame, "details");
+    ASSERT_NE(docA, nullptr);
+    ASSERT_NE(docB, nullptr);
+    ASSERT_NE(details, nullptr);
+
+    EXPECT_TRUE(docA->attached);
+    EXPECT_TRUE(docA->visible);
+    EXPECT_TRUE(docA->active);
+    EXPECT_TRUE(docA->focused);
+
+    EXPECT_TRUE(docB->attached);
+    EXPECT_FALSE(docB->visible);
+    EXPECT_FALSE(docB->active);
+    EXPECT_FALSE(docB->focused);
+
+    EXPECT_TRUE(details->attached);
+    EXPECT_TRUE(details->visible);
+    EXPECT_FALSE(details->active);
+    EXPECT_FALSE(details->focused);
+
+    const std::vector<std::string> expectedEvents = {
+        "Attached:doc-a",
+        "Attached:doc-b",
+        "Attached:details",
+        "Shown:doc-a",
+        "Shown:details",
+        "Activated:doc-a",
+        "FocusGained:doc-a"
+    };
+    EXPECT_EQ(FormatEvents(frame.events), expectedEvents);
+}
+
+TEST(UIEditorPanelHostLifecycleTest, HidingActiveTabKeepsPanelAttachedButEmitsVisibilityAndActivationTransitions) {
+    const UIEditorPanelRegistry registry = BuildPanelRegistry();
+    UIEditorWorkspaceModel workspace = BuildWorkspace();
+    UIEditorWorkspaceSession session =
+        BuildDefaultUIEditorWorkspaceSession(registry, workspace);
+
+    UIEditorPanelHostLifecycleState lifecycleState = {};
+    UpdateUIEditorPanelHostLifecycle(
+        lifecycleState,
+        registry,
+        workspace,
+        session,
+        UIEditorPanelHostLifecycleRequest{ "doc-a" });
+
+    ASSERT_TRUE(TryHideUIEditorWorkspacePanel(registry, workspace, session, "doc-a"));
+    const auto frame = UpdateUIEditorPanelHostLifecycle(
+        lifecycleState,
+        registry,
+        workspace,
+        session,
+        UIEditorPanelHostLifecycleRequest{ "doc-b" });
+
+    const auto* docA = FindUIEditorPanelHostState(frame, "doc-a");
+    const auto* docB = FindUIEditorPanelHostState(frame, "doc-b");
+    ASSERT_NE(docA, nullptr);
+    ASSERT_NE(docB, nullptr);
+
+    EXPECT_TRUE(docA->attached);
+    EXPECT_FALSE(docA->visible);
+    EXPECT_FALSE(docA->active);
+    EXPECT_FALSE(docA->focused);
+
+    EXPECT_TRUE(docB->attached);
+    EXPECT_TRUE(docB->visible);
+    EXPECT_TRUE(docB->active);
+    EXPECT_TRUE(docB->focused);
+
+    const std::vector<std::string> expectedEvents = {
+        "FocusLost:doc-a",
+        "Deactivated:doc-a",
+        "Hidden:doc-a",
+        "Shown:doc-b",
+        "Activated:doc-b",
+        "FocusGained:doc-b"
+    };
+    EXPECT_EQ(FormatEvents(frame.events), expectedEvents);
+}
+
+TEST(UIEditorPanelHostLifecycleTest, ClosingHiddenPanelEmitsDetachWithoutVisibilityTransitions) {
+    const UIEditorPanelRegistry registry = BuildPanelRegistry();
+    UIEditorWorkspaceModel workspace = BuildWorkspace();
+    UIEditorWorkspaceSession session =
+        BuildDefaultUIEditorWorkspaceSession(registry, workspace);
+
+    UIEditorPanelHostLifecycleState lifecycleState = {};
+    UpdateUIEditorPanelHostLifecycle(
+        lifecycleState,
+        registry,
+        workspace,
+        session,
+        UIEditorPanelHostLifecycleRequest{ "doc-a" });
+
+    ASSERT_TRUE(TryCloseUIEditorWorkspacePanel(registry, workspace, session, "doc-b"));
+    const auto frame = UpdateUIEditorPanelHostLifecycle(
+        lifecycleState,
+        registry,
+        workspace,
+        session,
+        UIEditorPanelHostLifecycleRequest{ "doc-a" });
+
+    const auto* docB = FindUIEditorPanelHostState(frame, "doc-b");
+    ASSERT_NE(docB, nullptr);
+    EXPECT_FALSE(docB->attached);
+    EXPECT_FALSE(docB->visible);
+    EXPECT_FALSE(docB->active);
+    EXPECT_FALSE(docB->focused);
+
+    const std::vector<std::string> expectedEvents = {
+        "Detached:doc-b"
+    };
+    EXPECT_EQ(FormatEvents(frame.events), expectedEvents);
+}
+
+TEST(UIEditorPanelHostLifecycleTest, ClearingFocusOnlyEmitsFocusLostAndReopeningPanelReattachesIt) {
+    const UIEditorPanelRegistry registry = BuildPanelRegistry();
+    UIEditorWorkspaceModel workspace = BuildWorkspace();
+    UIEditorWorkspaceSession session =
+        BuildDefaultUIEditorWorkspaceSession(registry, workspace);
+
+    UIEditorPanelHostLifecycleState lifecycleState = {};
+    UpdateUIEditorPanelHostLifecycle(
+        lifecycleState,
+        registry,
+        workspace,
+        session,
+        UIEditorPanelHostLifecycleRequest{ "doc-a" });
+
+    const auto focusLostFrame = UpdateUIEditorPanelHostLifecycle(
+        lifecycleState,
+        registry,
+        workspace,
+        session,
+        UIEditorPanelHostLifecycleRequest{});
+    EXPECT_EQ(
+        FormatEvents(focusLostFrame.events),
+        std::vector<std::string>({ "FocusLost:doc-a" }));
+
+    ASSERT_TRUE(TryCloseUIEditorWorkspacePanel(registry, workspace, session, "doc-b"));
+    UpdateUIEditorPanelHostLifecycle(
+        lifecycleState,
+        registry,
+        workspace,
+        session,
+        UIEditorPanelHostLifecycleRequest{});
+
+    ASSERT_TRUE(TryOpenUIEditorWorkspacePanel(registry, workspace, session, "doc-b"));
+    const auto reopenFrame = UpdateUIEditorPanelHostLifecycle(
+        lifecycleState,
+        registry,
+        workspace,
+        session,
+        UIEditorPanelHostLifecycleRequest{ "doc-b" });
+
+    const std::vector<std::string> expectedEvents = {
+        "Deactivated:doc-a",
+        "Hidden:doc-a",
+        "Attached:doc-b",
+        "Shown:doc-b",
+        "Activated:doc-b",
+        "FocusGained:doc-b"
+    };
+    EXPECT_EQ(FormatEvents(reopenFrame.events), expectedEvents);
+}