fix(router.py): support context window fallbacks for pre-call checks

litellm/router.py

@@ -2210,6 +2210,18 @@ class Router:
                 ):
                     invalid_model_indices.append(idx)
 
+        if len(invalid_model_indices) == len(_returned_deployments):
+            """
+            - no healthy deployments available b/c context window checks
+            """
+            raise litellm.ContextWindowExceededError(
+                message="Context Window exceeded for given call",
+                model=model,
+                llm_provider="",
+                response=httpx.Response(
+                    status_code=400, request=httpx.Request("GET", "https://example.com")
+                ),
+            )
         if len(invalid_model_indices) > 0:
             for idx in reversed(invalid_model_indices):
                 _returned_deployments.pop(idx)