fix(cli): initialize ctx_len before compact banner path

tests/test_cli_context_warning.py

@@ -145,3 +145,15 @@ class TestLowContextWarning:
         calls = [str(c) for c in cli_obj.console.print.call_args_list]
         warning_calls = [c for c in calls if "too low" in c]
         assert len(warning_calls) == 0
+
+    def test_compact_banner_does_not_crash_on_narrow_terminal(self, cli_obj):
+        """Compact mode should still have ctx_len defined for warning logic."""
+        cli_obj.agent.context_compressor.context_length = 4096
+
+        with patch("shutil.get_terminal_size", return_value=os.terminal_size((70, 40))), \
+             patch("cli._build_compact_banner", return_value="compact banner"):
+            cli_obj.show_banner()
+
+        calls = [str(c) for c in cli_obj.console.print.call_args_list]
+        warning_calls = [c for c in calls if "too low" in c]
+        assert len(warning_calls) == 1