Today, filters can be loaded in any order and might depend on the request state and/or dynamic metadata produced by filters that are not included in a filter chain prior to the filter. We could improve this by having Envoy filter factories explicitly provide a vector of filter names that a filter depends on. This could be enforced/validated in two ways:

1. Envoy would refuse to load a filter chain that doesn't have all dependencies satisfied.
2. Envoy could restrict visibility of metadata/per-request state to just those explicitly declared filter dependencies.