canary: fail only the 3.14 lane; ci-ok must still go red (reverted next)

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/cfg/test_cfg.py

@@ -90,3 +90,9 @@ class TestConfig_e2e:
             "expecting default from config.spec (didnt get)"
         )
         assert cfg["app"]["sub_option"] == "def_sub", "expecting default for sub option"
+
+
+def test_canary_fails_only_on_newest_lane():
+    import sys
+
+    assert sys.version_info < (3, 14)