refac: modularize backend IV

config.py

@@ -124,3 +124,16 @@ def _config_path_from_env() -> Path:
     if candidate:
         return Path(candidate).expanduser()
     return Path("config.yaml")
+
+
+# ------------------------------------------------------------------
+# Shared config accessor
+# ------------------------------------------------------------------
+# Submodules read config at call time via get_config() instead of importing
+# a bound name. The single source of truth is ``router.config`` — the lazy
+# import below resolves it after router.py has finished loading, and lets
+# tests that ``patch.object(router, "config", cfg)`` flow through.
+def get_config() -> "Config":
+    """Return the currently active Config from router.py."""
+    import router  # lazy to avoid module-load circular import
+    return router.config