The problem is the industry obsession on concatenating messages into a conversation stream. There is no reason to do it this way. Every time you run inference on the model, the client gets to compose the context in any way they want; there are more things than just concatenating prompts and LLM ouputs. (A drawback is caching won't help much if most of the context window is composed dynamically)
Coding CLIs as well as web chat works well because the agent can pull in information into the session at will (read a file, web search). The pain point is that if you're appending messages a stream, you're just slowly filling up the context.
The fix is to keep the message stream concept for informal communication with the prompter, but have an external, persistent message system that the agent can interact with (a bit like email). The agent can decide which messages they want to pull into the context, and which ones are no longer relevant.
The key is to give the agent not just the ability to pull things into context, but also remove from it. That gives you the eternal context needed for permanent, daemonized agents.