test(frontend): keep saved-session boot coverage aligned (#4961)

tests/test_new_chat_default_model_frontend.py

@@ -60,7 +60,8 @@ def test_hard_refresh_hydrates_saved_session_model_before_revealing_model_chip()
     boot_js = Path("static/boot.js").read_text(encoding="utf-8")
     load_marker = "await loadSession(saved, {preserveActiveInput:true});"
     assert load_marker in boot_js
-    saved_restore = boot_js[boot_js.index(load_marker) : boot_js.index("await checkInflightOnBoot(saved);return;", boot_js.index(load_marker))]
+    restore_end = "await checkInflightOnBoot(saved);"
+    saved_restore = boot_js[boot_js.index(load_marker) : boot_js.index(restore_end, boot_js.index(load_marker))]
     assert "await _startBootModelDropdown();" in saved_restore
     assert saved_restore.index("await _startBootModelDropdown();") > saved_restore.index(load_marker)
     assert saved_restore.index("await _startBootModelDropdown();") < saved_restore.index("S._bootReady=true;"), (