A piece of context that must be retrieved from a separate system is a piece of context that will not be retrieved. The friction of lookup — knowing the system exists, knowing how to query it, having access credentials, maintaining the mapping between context and artifact — is enough to make the context practically inaccessible for most use cases. Context that is simply present, in the same place as the artifact it describes, gets used. This is why comments in code are read and documentation in wikis is not. Co-location is not a convenience — it is the property that determines whether context exists in practice or only in theory.
(Agent traces are first-class artifact of software development)