diff --git a/packages/kaya-core/src/kaya/core/_mixin.py b/packages/kaya-core/src/kaya/core/_mixin.py
index fd9444b..f743939 100644
--- a/packages/kaya-core/src/kaya/core/_mixin.py
+++ b/packages/kaya-core/src/kaya/core/_mixin.py
@@ -29,9 +29,22 @@ class KayaMixin(ABC):
         pass
 
     def setup(self, loop: AbstractEventLoop) -> None:
-        """Called on lifespan startup (default: no-op)."""
+        """Called on lifespan startup (default: no-op).
+
+        Under RSGI (granian) the loop is NOT yet running when this is
+        called: schedule work on the passed ``loop`` (e.g.
+        ``loop.create_task``) instead of calling
+        ``asyncio.get_running_loop()``, which raises ``RuntimeError``
+        there. Under ASGI the lifespan runs inside a coroutine, so a
+        running loop happens to be available — do not rely on that.
+        """
         pass
 
     def shutdown(self, loop: AbstractEventLoop) -> None:
-        """Called on lifespan shutdown (default: no-op)."""
+        """Called on lifespan shutdown (default: no-op).
+
+        As with :meth:`setup`, use the passed ``loop``; it may already be
+        stopped under RSGI, so ``asyncio.get_running_loop()`` is not
+        reliable here either.
+        """
         pass