We wouldn't have identities either if we were all clones and our memories could be edited and shuffled at each conversation.

For an agent to have an identity we would have to intentionally make it hard to context engineering and limit it to append only messages that mimick human communication.

I can implant a thought into your head. If I say "Don't think about a green elephant" for a moment you'll think about a green elephant. There are more sophisticated examples of a person implanting thoughts in somobodies head (e.g. propaganda) but that's about it, I can't literally edit thoughts.

Why on earth do we want to limit our ability to do more powerful context engineering in a substrate that offers that ability natively?

Presumably because for some use cases you want the context of an agent to belong to a different "administrative domain" and you so want to have control over what information reaches it and how can it affect it?

Agent identity is just OAuth in a fake mustache. I suspect the real boundary is not agent-to-agent, but context + permissions + audit trail.