Per conversation at MobySummit with @stevvooe @Random-Liu :

Need an "ensure" or "verify" function in the client library to properly walk an image's components to verify all pulled/unpacked and in a "ready" state to be used, e.g., for a container start referenced against that image ref. Without this, it is possible today to rely on an image whose reference is in the content store but whose components may or may not be ready/fully unpacked.