fix: refresh quotes without blocking UI

tests/test_ui.py

@@ -1,4 +1,7 @@
 from decimal import Decimal
+import time
+
+from grid_trading.domain.models import Instrument
 
 
 def test_formatters_render_money_percent_and_empty_values():
@@ -30,3 +33,40 @@ def test_main_window_can_be_constructed_offscreen(tmp_path, monkeypatch):
     window.close()
     service.close()
     app.processEvents()
+
+
+def test_quote_refresh_does_not_block_main_window(tmp_path, monkeypatch):
+    monkeypatch.setenv("QT_QPA_PLATFORM", "offscreen")
+
+    from PySide6.QtWidgets import QApplication
+
+    from grid_trading.services.trading_service import TradingService
+    from grid_trading.ui.main_window import MainWindow
+
+    class SlowQuoteProvider:
+        def fetch_quotes(self, instruments):
+            time.sleep(0.3)
+            return {}
+
+    app = QApplication.instance() or QApplication([])
+    service = TradingService(tmp_path / "grid.db", quote_provider=SlowQuoteProvider())
+    service.ensure_defaults()
+    service.add_instrument(Instrument(id=None, code="000001", name="Ping An Bank"))
+    window = MainWindow(service)
+
+    started_at = time.perf_counter()
+    window._refresh_quotes()
+    elapsed = time.perf_counter() - started_at
+
+    assert elapsed < 0.15
+
+    deadline = time.perf_counter() + 2
+    while getattr(window, "_quote_thread", None) is not None and time.perf_counter() < deadline:
+        app.processEvents()
+        time.sleep(0.01)
+
+    assert getattr(window, "_quote_thread", None) is None
+
+    window.close()
+    service.close()
+    app.processEvents()