fix: fit main window within screen on startup

tests/test_gui.py

@@ -17,7 +17,7 @@ from app import accounts, ai, appconfig, db, prompts
 if gui.QT_IMPORT_ERROR is not None:
     raise unittest.SkipTest("PySide6 未安装")
 
-from PySide6.QtCore import QItemSelectionModel
+from PySide6.QtCore import QItemSelectionModel, QRect
 from PySide6.QtGui import QTextCursor
 from PySide6.QtWidgets import QApplication, QCheckBox, QLineEdit, QPlainTextEdit, QProgressBar, QTableView
 
@@ -39,6 +39,7 @@ from app.gui import (
     TAB_TITLES,
     WriteBackWorker,
 )
+from app.gui.main_window import _fit_and_center_window
 
 
 class GuiTests(TempDirMixin, unittest.TestCase):
@@ -182,6 +183,42 @@ class GuiTests(TempDirMixin, unittest.TestCase):
 
         self.assert_removed(temp_dir)
 
+    def test_main_window_initial_fit_limits_size_on_small_screen(self):
+        class FakeWindow:
+            def __init__(self):
+                self.size = None
+                self.position = None
+
+            def resize(self, width, height):
+                self.size = (width, height)
+
+            def move(self, x, y):
+                self.position = (x, y)
+
+        window = FakeWindow()
+        _fit_and_center_window(window, available_geometry=QRect(0, 0, 900, 700))
+
+        self.assertEqual((820, 620), window.size)
+        self.assertEqual((40, 40), window.position)
+
+    def test_main_window_initial_fit_centers_preferred_size_on_large_screen(self):
+        class FakeWindow:
+            def __init__(self):
+                self.size = None
+                self.position = None
+
+            def resize(self, width, height):
+                self.size = (width, height)
+
+            def move(self, x, y):
+                self.position = (x, y)
+
+        window = FakeWindow()
+        _fit_and_center_window(window, available_geometry=QRect(100, 50, 1600, 900))
+
+        self.assertEqual((1180, 760), window.size)
+        self.assertEqual((310, 120), window.position)
+
     def test_collect_tab_shows_empty_state_without_accounts(self):
         with self.make_temp_dir() as temp_dir:
             cfg = self.make_config(temp_dir)