Move qt conf env var setting earlier into startup

Maybe that will convince webengine to use it

src/calibre/constants.py

@@ -411,6 +411,9 @@ if getattr(sys, 'frozen', False):
         is_running_from_develop = running_in_develop_mode()
 
 in_develop_mode = os.getenv('CALIBRE_ENABLE_DEVELOP_MODE') == '1'
+if iswindows:
+    # Needed to get Qt to use the correct cache dir, relies on a patched Qt
+    os.environ['CALIBRE_QT_CACHE_LOCATION'] = cache_dir()
 
 
 def get_version():

src/calibre/gui2/__init__.py

@@ -23,9 +23,8 @@ from threading import Lock, RLock
 import calibre.gui2.pyqt6_compat as pqc
 from calibre import as_unicode, prints
 from calibre.constants import (
-    DEBUG, __appname__ as APP_UID, __version__, cache_dir, config_dir,
+    DEBUG, __appname__ as APP_UID, __version__, config_dir, is_running_from_develop,
-    is_running_from_develop, isbsd, isfrozen, islinux, ismacos, iswindows, isxp,
+    isbsd, isfrozen, islinux, ismacos, iswindows, isxp, plugins_loc
-    plugins_loc
 )
 from calibre.ebooks.metadata import MetaInformation
 from calibre.gui2.linux_file_dialogs import (
@@ -1052,8 +1051,6 @@ class Application(QApplication):
             if gprefs['color_palette'] != 'system':
                 set_appearance(gprefs['color_palette'])
         self.ignore_palette_changes = False
-        if iswindows:
-            os.environ['CALIBRE_QT_CACHE_LOCATION'] = cache_dir()
         QNetworkProxyFactory.setUseSystemConfiguration(True)
         # Allow import of webengine after construction of QApplication on new
         # enough PyQt

src/calibre/gui2/tweak_book/main.py

@@ -7,7 +7,6 @@ import sys
 import time
 
 from qt.core import QIcon
-from qt.webengine import QWebEngineUrlScheme
 
 from calibre.constants import EDITOR_APP_UID, FAKE_PROTOCOL, islinux
 from calibre.ebooks.oeb.polish.check.css import shutdown as shutdown_css_check_pool
@@ -51,6 +50,7 @@ def gui_main(path=None, notify=None):
 
 
 def _run(args, notify=None):
+    from qt.webengine import QWebEngineUrlScheme
     # Ensure we can continue to function if GUI is closed
     os.environ.pop('CALIBRE_WORKER_TEMP_DIR', None)
     reset_base_dir()

src/calibre/gui2/viewer/main.py

@@ -7,7 +7,6 @@ import os
 import sys
 from contextlib import closing
 from qt.core import QIcon, QObject, Qt, QTimer, pyqtSignal
-from qt.webengine import QWebEngineUrlScheme
 
 from calibre.constants import FAKE_PROTOCOL, VIEWER_APP_UID, islinux
 from calibre.gui2 import Application, error_dialog, setup_gui_option_parser
@@ -168,6 +167,7 @@ def run_gui(app, opts, args, internal_book_data, listener=None):
 
 
 def main(args=sys.argv):
+    from qt.webengine import QWebEngineUrlScheme
     # Ensure viewer can continue to function if GUI is closed
     os.environ.pop('CALIBRE_WORKER_TEMP_DIR', None)
     reset_base_dir()