diff --git a/booru_viewer/gui/app.py b/booru_viewer/gui/app.py
deleted file mode 100644
index d546b5d..0000000
--- a/booru_viewer/gui/app.py
+++ /dev/null
@@ -1,60 +0,0 @@
-"""Main Qt6 application window."""
-
-from __future__ import annotations
-
-import asyncio
-import logging
-import os
-import sys
-import threading
-from pathlib import Path
-
-from PySide6.QtCore import Qt, QTimer, Signal, QObject, QUrl, Property
-from PySide6.QtGui import QPixmap, QAction, QKeySequence, QDesktopServices, QShortcut, QColor
-from PySide6.QtWidgets import (
-    QApplication,
-    QMainWindow,
-    QWidget,
-    QVBoxLayout,
-    QHBoxLayout,
-    QStackedWidget,
-    QComboBox,
-    QLabel,
-    QPushButton,
-    QStatusBar,
-    QSplitter,
-    QMessageBox,
-    QTextEdit,
-    QMenu,
-    QFileDialog,
-    QSpinBox,
-    QScrollArea,
-    QProgressBar,
-)
-
-from dataclasses import dataclass, field
-
-from ..core.db import Database, Site
-from ..core.api.base import BooruClient, Post
-from ..core.api.detect import client_for_type
-from ..core.cache import download_image, download_thumbnail, cache_size_bytes, evict_oldest, evict_oldest_thumbnails
-from ..core.config import MEDIA_EXTENSIONS
-
-from .grid import ThumbnailGrid
-from .preview import ImagePreview
-from .search import SearchBar
-from .sites import SiteManagerDialog
-from .bookmarks import BookmarksView
-from .library import LibraryView
-from .settings import SettingsDialog
-
-log = logging.getLogger("booru")
-
-
-# -- Refactor compatibility shims (deleted in commit 14) --
-from .search_state import SearchState  # re-export for refactor compat
-from .log_handler import LogHandler  # re-export for refactor compat
-from .async_signals import AsyncSignals  # re-export for refactor compat
-from .info_panel import InfoPanel  # re-export for refactor compat
-from .main_window import BooruApp  # re-export for refactor compat
-from .app_runtime import run  # re-export for refactor compat
diff --git a/booru_viewer/gui/main_window.py b/booru_viewer/gui/main_window.py
index 60d85fd..a545a85 100644
--- a/booru_viewer/gui/main_window.py
+++ b/booru_viewer/gui/main_window.py
@@ -41,7 +41,7 @@ from ..core.cache import download_image, download_thumbnail, cache_size_bytes, e
 from ..core.config import MEDIA_EXTENSIONS
 
 from .grid import ThumbnailGrid
-from .preview import ImagePreview
+from .preview_pane import ImagePreview
 from .search import SearchBar
 from .sites import SiteManagerDialog
 from .bookmarks import BookmarksView
@@ -1130,7 +1130,7 @@ class BooruApp(QMainWindow):
             # the entire multi-MB file to land. Cached videos go through
             # the normal flow because the local path is already there.
             from ..core.cache import is_cached
-            from .preview import VIDEO_EXTENSIONS
+            from .media.constants import VIDEO_EXTENSIONS
             is_video = bool(
                 post.file_url
                 and Path(post.file_url.split('?')[0]).suffix.lower() in VIDEO_EXTENSIONS
@@ -2058,7 +2058,7 @@ class BooruApp(QMainWindow):
         idx = self._grid.selected_index
         if 0 <= idx < len(self._posts):
             self._info_panel.set_post(self._posts[idx])
-        from .preview import FullscreenPreview
+        from .popout.window import FullscreenPreview
         # Restore persisted window state
         saved_geo = self._db.get_setting("slideshow_geometry")
         saved_fs = self._db.get_setting_bool("slideshow_fullscreen")
@@ -2132,7 +2132,7 @@ class BooruApp(QMainWindow):
     def _on_fullscreen_closed(self) -> None:
         # Persist popout window state to DB
         if self._fullscreen_window:
-            from .preview import FullscreenPreview
+            from .popout.window import FullscreenPreview
             fs = FullscreenPreview._saved_fullscreen
             geo = FullscreenPreview._saved_geometry
             self._db.set_setting("slideshow_fullscreen", "1" if fs else "0")
diff --git a/booru_viewer/gui/preview.py b/booru_viewer/gui/preview.py
deleted file mode 100644
index c3ffaaa..0000000
--- a/booru_viewer/gui/preview.py
+++ /dev/null
@@ -1,28 +0,0 @@
-"""Full media preview — image viewer with zoom/pan and video player."""
-
-from __future__ import annotations
-
-import logging
-from pathlib import Path
-from typing import NamedTuple
-
-from PySide6.QtCore import Qt, QPointF, QRect, Signal, QTimer, Property
-from PySide6.QtGui import QPixmap, QPainter, QWheelEvent, QMouseEvent, QKeyEvent, QMovie, QColor
-from PySide6.QtWidgets import (
-    QWidget, QVBoxLayout, QHBoxLayout, QLabel, QMainWindow,
-    QStackedWidget, QPushButton, QSlider, QMenu, QInputDialog, QStyle,
-)
-
-import mpv as mpvlib
-
-_log = logging.getLogger("booru")
-
-
-# -- Refactor compatibility shims (deleted in commit 14) --
-from .media.constants import VIDEO_EXTENSIONS, _is_video  # re-export for refactor compat
-from .popout.viewport import Viewport, _DRIFT_TOLERANCE  # re-export for refactor compat
-from .media.image_viewer import ImageViewer  # re-export for refactor compat
-from .media.mpv_gl import _MpvGLWidget, _MpvOpenGLSurface  # re-export for refactor compat
-from .media.video_player import _ClickSeekSlider, VideoPlayer  # re-export for refactor compat
-from .popout.window import FullscreenPreview  # re-export for refactor compat
-from .preview_pane import ImagePreview  # re-export for refactor compat
diff --git a/booru_viewer/main_gui.py b/booru_viewer/main_gui.py
index b0c8660..e4687b6 100644
--- a/booru_viewer/main_gui.py
+++ b/booru_viewer/main_gui.py
@@ -35,7 +35,7 @@ def main() -> None:
                 file=sys.stderr,
             )
 
-    from booru_viewer.gui.app import run
+    from booru_viewer.gui.app_runtime import run
     run()